Endoscopic Endonasal Pituitary and Skull Base Surgery

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Chapter 22 Endoscopic Endonasal Pituitary and Skull Base Surgery

David H. Jho, Diana H. Jho, Hae-Dong Jho

Neuroendoscopy was first implemented almost a century ago for choroid plexus surgery in a patient with hydrocephalus. General enthusiasm for ventricular endoscopy experienced an initial decline with the advent of ventricular shunt systems but was later revived for third ventriculostomies in selected patients. The first reported use of the endoscope specifically for trans-sphenoidal surgery was in a sublabial approach by Guiot and colleagues in 1963.¹ However, the general advancement of intracranial and spinal neuroendoscopy continued to be limited, in part trumped by historical developments in neuroimaging and microneurosurgery. Yet in the past three decades, a few pioneering endoscopic neurosurgeons continued to expand and refine the use of neuroendoscopy in endoscope-assisted microsurgery, endonasal trans-sphenoidal surgery, ventricular tumor surgery, extra-axial intracranial surgery, intra-axial brain surgery with stereotactic guidance, and spinal surgery. These advances were accompanied by concurrent technological developments in endoscopic optics, video-imaging systems, endoscopic accessory attachments for neurosurgical applications, specialized neuroendoscopic surgical instruments, radiologic imaging, and compatible frameless stereotactic image-guided systems. As neuroendoscopic surgical techniques and equipment have co-evolved, the addition of neuroendoscopy to the repertoire of the modern neurosurgeon has become increasingly practical. Of note, general interest has noticeably grown for the use of neuroendoscopy in endonasal trans-sphenoidal pituitary surgery, and the common use of neuroendoscopy in pituitary surgery became truly practical in recent years with the development of commercially-available neuroendoscopic equipment.

Although the removal of pituitary tumors completely through endoscopic visualization via an endonasal route has been a relatively recent development, the use of the endonasal pathway itself was initially reported in 1909 by Hirsch who performed his first pituitary surgery in Vienna by approaching the sella through an endonasal route using multiple-staged sinonasal operations with naked-eye visualization. Despite his first endonasal trans-sphenoidal surgery having reported success, Hirsch subsequently converted to a trans-septal submucosal approach, possibly due to fear of surgical infection through such a wide communication made between the nasal and the cranial cavity. Griffith and Veerapen revisited the endonasal approach in 1987, with insertion of a trans-sphenoidal retractor through the natural nasal airway to the sphenoid rostrum for microscopic pituitary surgery.² In 1994, Cooke and Jones reported the lack of sinonasal and dental complications when an endonasal route was adopted for microscopic pituitary surgery.³ But the most significant progression of the traditional sublabial and transfixional-trans-septal approaches to the direct endonasal route was highly facilitated by the neuroendoscope, with the initial use of sinonasal endoscopy in Europe four decades ago. In the field of Otolaryngology, the introduction of endoscopic sinus surgery to the United States kindled an evolution in surgical techniques such that endoscopic sinus surgery rapidly replaced many forms of conventional sinus surgery, with radical changes in concepts of sinonasal pathophysiology and associated treatments aided by endoscopic exploration. Rather than stripping the infected sinus mucosa as was done in conventional sinus surgery, endoscopic sinus surgery aimed to restore physiologic mucous drainage merely by eliminating obstructive pathoanatomy at sinus ostia via the endonasal route and became popularized as functional endoscopic sinus surgery (FESS). Successful advances in sinonasal endoscopy then enhanced interest in the use of endoscopy for trans-sphenoidal surgery. Endoscopic trans-sphenoidal surgery started with guidance during simple biopsy of a sellar lesion, and then evolved to assist visualization during insertion of trans-sphenoidal retractors or during microscopic removal of pituitary adenomas, and eventually the pure form of endoscopic endonasal pituitary tumor surgery emerged.⁴^–¹²

This chapter describes endoscopic endonasal trans-sphenoidal surgery (EE-TS) along with related endoscopic endonasal approaches to the midline skull base such as the anterior cranial fossa (EE-ACF), optic nerve or cavernous sinus (EE-CS), pterygoid fossa or petrous apex (EE-Pterygoid or EE-Petrous), clivus or posterior fossa (EE-PFossa), and craniocervical junction (EE-CC junction). EE-TS is not merely endoscope-assisted microscopic surgery but is rather an operation done completely with an endoscope without any trans-sphenoidal retractor or nasal speculum, eliminating the need for postoperative nasal packing or other adjuncts. The physical nature of an endoscope with its optics at the tip and slender shaft allows simple access to the sella through the natural nasal air pathway via a nostril. EE-TS uses an endonasal route to the rostrum of the sphenoid sinus with an anterior sphenoidotomy about 1 to 1.5 cm in diameter. The wide-angled panoramic view, angled-lens views, and a close-up zoom-in view provide optical advantages with distinct visualization at the surgical target site. The application of principles and anatomy in EE-TS was extended to the surgical treatment of midline skull base pathologies (from the anterior cranial fossa to the clivus and posterior fossa along with the craniocervical junction) and paramedian skull base pathologies (from the optic nerve and cavernous sinus regions to the pterygoid fossa and petrous tip). Endoscopic endonasal techniques can potentially be applied to nearly any lesion within approximately 2-cm width of the midline skull base from the crista galli at the anterior-superior skull base to the foramen magnum and atlantoaxial region at the posterior-inferior skull base.¹³^–²³

Preoperative Management and Surgical Indications

As with microscopic pituitary surgery, all patients with pituitary adenomas undergo formal endocrine evaluations preoperatively and postoperatively. Hypopituitarism is among the important endocrine conditions requiring treatment starting preoperatively, particularly for hypocortisolism and hypothyroidism. For patients with preoperative visual symptoms or tumors impinging on the optic apparatus on magnetic resonance imaging (MRI), formal neuro-ophthalmologic evaluation is obtained preoperatively with follow-up visual examinations postoperatively. MRI of the brain with and without contrast enhancement (ideally with a pituitary focused protocol and optionally with dynamic contrast imaging) is the diagnostic imaging modality of choice with best resolution for most pituitary adenomas. Patients who are unable to undergo MRI for various reasons can undergo the lesser alternative of computed tomography (CT) of the brain with pituitary focus and dynamic contrast protocol. Usually, the basic anatomy of the paranasal sinuses and any variations of an individual can be appreciated sufficiently on MRI for the purposes of trans-sphenoidal surgery. However, bone windowed CT scans with fine-cut axial and coronal views can disclose the bony anatomy of the paranasal sinuses in detail and may be obtained depending on surgeon’s preference or for patients who have had previous paranasal sinus or trans-sphenoidal surgery. Image-guided systems (IGS) are not routinely required for EE-TS, but imaging protocol compatible with frameless stereotaxy may also be used for complex skull base lesions if desired.

Surgical indications for patients with pituitary adenomas to undergo endoscopic trans-sphenoidal surgery are essentially comparable to indications for conventional microscopic trans-sphenoidal surgery. Patients with hormonally inactive or nonfunctional pituitary adenomas are operated upon when the tumors cause symptomatic compression of the optic apparatus, hypopituitarism, pituitary apoplexy, or severe intractable frontotemporal headaches. Patients with hormonally active or functional pituitary adenomas causing acromegaly, Cushing’s disease, or hyperthyroidism undergo trans-sphenoidal surgery as the primary mode of treatment. Patients with prolactinomas are operated upon only when they fail to respond appropriately to dopaminergic medications, develop intolerable side effects to the medications, or choose against the use of dopaminergic medications. Other symptomatic mass lesions or tumors at the pituitary fossa generally undergo surgery if needed for biopsy or resection. In contrast to conventional microscopic surgery, a large pituitary tumor with suprasellar extension can be directly visualized in EE-TS and bony exposure can be extended rostrally if further exploration at the planum sphenoidale is required. EE-TS can thus enhance the chance for total pituitary tumor resection and potentially reduce the need of a supplemental transcranial approach.

Following hundreds of EE-TS cases with the youngest patient being a teenager, we have yet to encounter a patient whose nasal passage was too small or narrow to undergo standard EE-TS. Notably, patients with acromegaly usually have hypertrophic turbinates and nasal-oral soft tissues such that the endonasal space can be disproportionately small. In addition, patients with Cushing’s disease often have narrow nasal airways due to swollen hypertrophic mucosa, which also tends to bleed easily. Among our patients who have undergone EE-TS, two patients with Cushing’s disease required a two-nostril technique with an endoscope inserted through one nostril and the surgical instruments inserted through the other. Reoperation by EE-TS for patients who have undergone previous conventional trans-sphenoidal surgery is not difficult if an appropriate anterior sphenoidotomy was previously performed, although reoperation can be challenging if bony sellar structures were excessively eliminated, complications were encountered at previous surgery, or distorting extensive reconstruction was performed.

Pertinent Sinonasal Anatomy

To perform endoscopic pituitary surgery, the functional physiology and anatomy of the sinonasal cavity must be understood. In the paranasal sinuses (that include the sphenoid, ethmoid, maxillary, and frontal sinuses), mucociliary movement is orchestrated by the delivery of mucus flow to the sinus ostia. From the sinus ostia, nasal mucosal ciliary movement is directed to establish the physiologic flow of mucus towards the nasopharynx. When the path of physiologic mucus flow is interrupted mechanically or functionally, the paranasal sinuses can retain stagnant mucus, which can subsequently become infected and result in sinusitis. The confluence of the draining mucus from the frontal sinus, anterior ethmoidal sinus, and maxillary sinus is located at the middle meatus. Mucosal drainage of the posterior ethmoidal sinus occurs at the superior meatus, and drainage of the sphenoid sinus is at the sphenoethmoidal recess, which is located between the posterolateral aspect of the middle turbinate, superior turbinate, and the rostrum of the sphenoid sinus.

The nasal cavity itself is bordered medially by the nasal septum (comprised of the septal cartilage, perpendicular plate of the ethmoid bone, and the vomer); superiorly by the cribriform plate of the ethmoid bone and bridge of the nose (consisting of the nasal portion of the frontal bone, nasal bone, and frontal process of the maxilla); inferiorly by the floor of the nasal cavity (involving the palatine process of the maxilla and the horizontal plate of the palatine bone); and conchae or turbinates laterally (inferior, middle, superior, and sometimes supreme turbinates). The superior and middle conchae (along with the occasional supreme concha) are components of the ethmoid bone, whereas the inferior concha is a separate bone. The EE-TS procedure traverses the region medial to the middle turbinate, between the middle turbinate and the nasal septum, on the way to the sphenoid sinus then the pituitary fossa at the sella turcica. Nasal septal deviation is not an uncommon phenomenon, such that often the larger nasal cavity is selected as the route for EE-TS based on preoperative imaging and intraoperative visualization.

The lateral wall of the endonasal route (with numerous projections of the ethmoid bone and individual anatomic variability) is more complex in anatomy than the medial wall, which consists of the nasal septum. From both a surgical and anatomic embryology standpoint, the ethmoid at the lateral wall of the nasal cavity has been divided into five sequential lamella from anterior to posterior consisting of the uncinate process, ethmoid bulla, basal lamella of the middle turbinate, basal lamella of the superior turbinate, and occasionally the basal lamella of the supreme turbinate (if present). The basal lamella of the middle turbinate divides the ethmoid sinuses into anterior and posterior air cells, and the middle turbinate attachments lie in three different planes with the anterior segment oriented along a sagittal plane (attached to the lateral portion of the cribriform plate superiorly), middle segment oriented along a coronal plane (attached to the lamina papyracea), and the posterior segment oriented nearly along an axial plane (attached to the medial wall of the maxillary sinus and perpendicular plate of the palatine bone). The normal sinonasal anatomy located laterally to the middle turbinate is referred to as the osteomeatal complex (OMC) and comprises a key set of structures for sinonasal function, forming the basis of FESS treatments for paranasal sinus pathologies.

The OMC consists of the middle turbinate, uncinate process, hiatus semilunaris, ethmoid infundibulum, and ethmoid bulla. Anterolateral to the middle turbinate is the uncinate process of the ethmoid bone, behind which lies a cleft between the uncinate and ethmoid bulla called the hiatus semilunaris, which is contiguous with the ethmoid infundibulum. The hiatus semilunaris is essentially a two-dimensional crescent-shaped opening leading from the middle meatus into the three-dimensional funnel-shaped ethmoid infundibulum to which the frontal sinus, anterior ethmoid sinus, and maxillary sinus usually drain. The frontal sinus drains anteriorly at the ethmoid infundibulum (via the hourglass-shaped frontonasal recess), anterior ethmoid sinus drains into the mid-portion, and the maxillary sinus drains through its ostium posteriorly at the maxillary infundibulum. Along the posterior-superior bank of the hiatus semilunaris is the ethmoid bulla, which is considered one of the most constant and largest of the anterior ethmoid air cells. The ethmoid bulla is bordered medially by the lamina papyracea of the medial orbit and projects medially in the middle meatus, and the posterior-superior portion of the hiatus semilunaris connects the middle meatus with the suprabullar and retrobullar recesses (collectively called the sinus lateralis), which are defined in relation to the ethmoid bulla. There are variations and debated nuances in the anatomic terminology of paranasal sinus anatomy, including the precise borders of the ethmoid infundibulum in relation to the hiatus semilunaris. Regardless, the more important point is that there are individual structural variations, which can affect paranasal sinus physiology and surgical anatomy. For instance, there are three major variations to the superior attachment of the crescent-shaped uncinate process with the most common type attaching laterally to the lamina papyracea (~70% in cadaveric studies) resulting in frontal sinus outflow medial to the uncinate process at the middle meatus. The two other major patterns of uncinate superior insertions include medial attachment to the base of the middle turbinate at the cribriform plate (<20%) and superior attachment to the roof of the ethmoid at the skull base (<10%) that both result in natural frontal sinus outflow lateral to the uncinate at the ethmoid infundibulum. There are other unmentioned variations of uncinate insertions, and these variations may be considered a continuous spectrum of lateral-to-medial insertions rather than merely categorical entities. Anatomic variations may also include a pneumatized or aerated turbinate, most frequently the middle turbinate, which is referred to as concha bullosa and can be enlarged. There can also be variations of a paradoxical middle turbinate with the convexity of the turbinate curve oriented laterally instead of medially, which can alter the expected configuration of the OMC. Regardless of these variations or the presence of any nasal polyps, the main point is that structures of the OMC should not be significantly disturbed en route to the sphenoid sinus during EE-TS. The sphenoid sinus mucosa should also be minimally disrupted by limiting the mucosal removal only to the region required at the anterior sphenoidotomy site and the anterior wall of the sella.

As mentioned, there can be significant variability in the structure of the ethmoid sinus, which is sometimes termed the ethmoid labyrinth, with the ethmoid air cells having some surgically pertinent variations for EE-TS. The agger nasi is a mound or prominence on the anterior-lateral aspect of the nasal cavity formed by mucous membrane covering the ethmoidal crest of the maxilla near the anterior aspect of the middle turbinate. The agger nasi cells are the most anterior ethmoidal cells located just anterior and lateral to the nasofrontal recess and can sometimes be involved in frontal sinus outflow obstruction. For EE-TS, the surgeon should be aware that a hyperpneumatized agger nasi cell can occasionally present as a bulge that mimics the anterior view of a turbinate. Haller cells (infraorbital ethmoid air cells or maxilloethmoidal cells) are closely related to the ethmoid infundibulum along the medial roof of the maxillary sinus, inferior-lateral to the ethmoid bulla, and extend into the inferomedial orbital floor at the inferior margin of the lamina papyracea. Since Haller cells are quite lateral, these usually do not present a problem during EE-TS, although their proximity to the ethmoid infundibulum can result in inadvertent orbital entry during FESS if not recognized. Onodi cells (sphenoethmoidal cells) are posterior ethmoidal air cells that can project superiorly into the sphenoid sinus towards the lateral side and can potentially be confused with a septated region of the sphenoid sinus. The optic nerve and/or internal carotid artery can bulge into Onodi cells instead of the sphenoid sinus proper, or occasionally may have either partial or complete bony dehiscence at the sphenoid sinus, presenting risk for injury during surgery. It is also possible to have extensive pneumatization of the anterior clinoid process at the optico-carotid recess (OCR), which can also expose the optic nerve and internal carotid artery to additional risk. It is also possible for patients who have undergone previous trans-sphenoidal surgery to have a mucocele at the region of the sphenoid sinus, which can also potentially lead to intraoperative confusion, although this is usually recognizable on the preoperative MRI with the mucocele usually having a spherical type of shape and bright T2 signal such that it can be anticipated intraoperatively.

The rostrum of the sphenoid sinus is usually a relatively constant midline landmark regardless of any bowing or lateral deviation of the nasal septum and can be used as a reference for drilling. However, the sphenoid sinuses internally are divided by a highly variable intersinus septum (or configuration of septae) that can be oblique, multiple, or incomplete, and usually does not strictly respect the sagittal midline. Sphenoid sinus septations are generally oriented in a vertical direction and may attach to the regions of the optic canal or carotid artery; septations that are horizontally oriented are usually boundaries between the posterior ethmoid sinus and the sphenoid sinus, which can include Onodi cells (sphenoethmoid air cells). Variations in the pneumatization of the sphenoid sinus, asymmetries, and septal divisions along with the relationship of the optic nerve and internal carotid arteries should be studied on the preoperative MRI and/or CT to serve as a roadmap to the sella. The thickness and position of the sella turcica, plus anatomy of the presellar and retrosellar recesses, and tumor extension in the suprasellar region and laterally to the region of the cavernous sinuses should be noted preoperatively to allow anticipatory maneuvers intraoperatively.

When the sphenoid sinus is entered with an endoscope, the complex anatomy is visualized in a panoramic fashion. The clival indentation is seen at the bottom midline, the bony protuberances covering the internal carotid arteries are lateral to the clival indentation, the sella is at the center, the cavernous sinuses are seen lateral to the sella, the tuberculum sella is at the top, and the bony protuberances of the optic nerves are seen laterally. Surgical landmarks for endoscopic endonasal pituitary surgery consist of the choanae and nasopharynx along with the inferior margin of the middle turbinate. The choana at the anterior-superior entry of the nasopharynx is always a useful landmark in order to confirm the middle turbinate. The extended line along the inferior margin of the middle turbinate leads to the region approximately 1 cm inferior to the sellar floor. Although the sphenoid sinus ostium at the sphenoethmoidal recess may also be visible under the endoscope, it may not always be easily identifiable or precisely consistent in its relationship to the sella. Thus, the sphenoid sinus ostium can be regarded as an inconsistent surgical landmark, whereas the choana and inferior margin of the middle turbinate tend to be quite consistent. Anterior sphenoidotomy measuring approximately 1.5 cm in diameter is performed at the rostrum of the sphenoid sinus at a location rostral to an extended line from the inferior margin of the middle turbinate (Fig. 22-1A and B).

FIGURE 22-1 Schematic drawings of the sinonasal cavity, coronal (A) and sagittal views (B), demonstrate the anatomic landmarks leading to the sella. The inferior turbinate (IT) and middle turbinate (MT) are initially encountered along the endonasal route. A plane followed along the inferior margin of the middle turbinate leads to the clivus approximately 1 cm inferior to the floor of the sella, and just inferiorly lies the upper margin of the choana with view of the nasopharynx that serves as a key surgical landmark. Confirmation of the middle turbinate in relation to the nasopharynx prevents any confusion of the middle turbinate with the superior turbinate (ST), which is especially important in occasional cases of an anatomic supreme turbinate. Fluoroscopic C-arm imaging is not necessary because of the consistency of these surgical landmarks.

Following pituitary tumor removal, the thin flaps of sellar bone are placed back into position to provide reconstruction at the anterior wall of the sella turcica. The sphenoid sinus is preserved as a natural air-filled cavity, and we routinely do not use any foreign surgical material at the sphenoid sinus (although reconstruction can be done with various materials or methods if absolutely needed for cerebrospinal fluid leaks or complex lesions involving significant bony defects). When an anterior sphenoidotomy is made, attention must be paid not to significantly disrupt the normal posterior mucus drainage channel at the sphenoid ostium of the sphenoethmoidal recess. Towards the conclusion of EE-TS, the middle turbinate is gently medialized back to its original position in order to avoid blockage of mucus drainage at the OMC.

The nasal mucosa is predominantly supplied by the sphenopalatine artery, with contributions from the greater palatine artery, branches of the facial artery, and the anterior and posterior ethmoidal arteries. The posterior septal artery arises from the sphenopalatine branch of the internal maxillary artery and passes to the posterior nasal septum at the inferior-medial aspect of the middle turbinate posterior margin. When surgical access is obtained between the middle turbinate and nasal septum for an anterior sphenoidotomy, the posterior septal artery often requires coagulation and division to prevent unwanted intraoperative or postoperative nasal bleeding. Delayed copious nasal bleeding after trans-sphenoidal surgery usually arises from rebleeding of the posterior septal artery.

For endoscopic endonasal approach to the anterior cranial fossa (EE-ACF), the region of the ethmoid roof with the cribriform plate and the fovea ethmoidalis should be studied on preoperative imaging. Keros categorized three types of skull base conformations along a spectrum depending on the depth of the olfactory sulcus and corresponding height of the lateral lamella, with Type 1 having 1-3 mm depth, Type 2 having 3-7 mm depth, and Type 3 having 7-16 mm depth such that the ethmoid roof is significantly higher than the cribriform plate.²⁴ The Keros classification is more pertinent for ethmoid sinus surgery to avoid inadvertent entry through the thin lateral lamella of the cribriform plate, especially for a deep olfactory sulcus. However, for EE-ACF or EE-CS (via the middle meatal approach with posterior ethmoidectomy), one should be aware of the potential individual variations in depth of the olfactory sulcus and the specific anatomic configuration should be noted preoperatively to assist with optimal intraoperative maneuvering. In the same region, the ethmoidal sulcus is the groove in the lateral lamella for the anterior ethmoidal artery, which branches from the ophthalmic artery and enters from the orbit in a bony canal in the ethmoid roof (anterior ethmoidal canal) or just below the level of the ethmoid roof to course anteromedially with the anterior ethmoidal nerve and to penetrate the lateral lamellae to supply the dura in the region of the olfactory sulcus. The posterior ethmoidal artery traverses the posterior ethmoidal canal within a 3 mm planar region above the cribriform plate. The anterior and posterior ethmoidal arteries usually provide the major blood supply for olfactory groove or planum sphenoidale meningiomas at the skull base.

Optical Advantages of an Endoscope

Wide-Angled Panoramic View

As trans-sphenoidal pituitary surgery began its evolvement in the 19^th century, one major advance was the adoption of the operating microscope in the 1960’s. The use of the endoscope for pituitary tumor resection represents another significant advancement. Whereas the operating microscope provides a magnified view of a limited portion of the sella through a narrow corridor revealed by the trans-sphenoidal retractor, an endoscope can physically enter into the sphenoid sinus and provide a wide-angled panoramic view with zooming capability. An operating microscope renders a tubular parallel beam view, but an endoscope shows a diverging flask-shaped wide-angled view (Fig. 22-2A to D). This wide-angled panoramic view is particularly useful for pituitary tumor surgery because it allows excellent anatomical visualization at the posterior wall of the sphenoid sinus. However, it must be recognized that the endoscopic view renders a fish-eye effect with maximum magnification at the center and relative contraction at the periphery with visualization of a wide anatomical area. In the well-pneumatized sphenoid sinus, the sella is readily recognizable at the center of the surgical view, and a panoramic image of the surrounding anatomy at the posterior wall of the sphenoid sinus is revealed under direct endoscopic view. Unless the region of the sella is not pneumatized or the patient is a complicated reoperation case, the use of fluoroscopic roentgenogram is not necessary since endoscopic visualization can adequately reveal the distinct surgical anatomy.

FIGURE 22-2 Schematic drawings demonstrate comparison views between microscopic and endoscopic exposure at the posterior wall of the sphenoid sinus during trans-sphenoidal pituitary surgery. The microscope view is stereoscopic but can be confined by the narrow tubular corridor for light projection to a central limited area of the sella (A, B). The endoscope view is monoscopic but reveals a wide region of the sphenoid sinus posterior wall due to the panoramic nature of endoscopic optics (C, D). The endoscope also has capabilities for dynamic visualization using freedom of endoscope movement at the surgical site and extra options for angled lenses. However, the endoscope lens does produce a degree of fish-eye effect with the center being maximally magnified and the periphery somewhat contracted. Endoscopic view demonstrates the sella (S) at the center, cavernous sinuses (Cs) laterally, the cavernous carotid arteries (Ca) inferolaterally, clivus (Cl) inferiorly, tuberculum sella (Ts) superiorly, and optic nerves (O) superolaterally.

Angled-Lens View

The angled-lens endoscopic view provides direct visualization of the anatomical corners such as the suprasellar area or towards the cavernous sinus. These views can be of great assistance even if an endoscope is only used as an adjunctive tool during conventional microscopic surgery. Operating under an angled-lens endoscopic view requires specially designed surgical tools and advanced endoscopic surgical skills, particularly for the 70-degree-lens endoscope. As an angled-lens endoscope is rotated towards the surgical target, various anatomical corners can be visualized from the floor of the sella to the medial wall of the cavernous sinus and towards the suprasellar region. A fiberoptic endoscope can sometimes be used to inspect anatomical corners involving curved routes. This angled view is advantageous when large suprasellar macroadenomas are to be removed. It also allows clear visualization at the medial wall of the cavernous sinus when the lateral margin of a sellar tumor abutting the cavernous sinus is dissected away or when tumor tissue invading the cavernous sinus is to be removed under direct visualization. Although pituitary adenomas with significant invasion of the cavernous sinus were once generally regarded as inoperable, EE-TS allows safe access to the cavernous sinus for tumor removal. Angled views allow for direct surgical access to the pterygoid fossa, anterior cranial fossa, clivus, and posterior cranial fossa in addition to the cavernous sinus (Fig. 22-3A and B).

FIGURE 22-3 Schematic drawings show angled views with the 30-degree-lens endoscope directed towards the suprasellar region (A, B). The 30-degree-lens endoscopic view discloses the anterior cerebral artery, optic chiasm (C), diaphragma sella (D), left optic nerve (LtO), right optic nerve (RtO), and pituitary stalk (S).

Close-Up Internal View

When tumor resection is accomplished, an endoscope can be advanced into the sella or suprasellar area close to the surgical target. This close-up view in liaison with zooming of the camera enhances the magnification of the surgical site. For microadenoma removal, the close-up view is utilized to confirm that the normal margin of the pituitary tissue is well-exposed at the tumor resection site. For macroadenomas, an endoscope can be advanced into the tumor resection cavity to visualize the internal anatomy at the resection cavity. When a 30-degree angled endoscope is inserted into the cavity and rotated through a full revolution, it can visualize the entire circumference of the cavity. Often a minute amount of tumor residue is revealed at the hidden corners for completion of removal. These close-up magnified views thus enhance complete tumor removal in microadenomas as well as macroadenomas.

Physical Advantages of an Endoscope

Endoscopes can be subdivided into two categories: fiberoptic flexible endoscopes and rod-lens rigid endoscopes. The number of fiberoptic fibers in most flexible endoscopes is approximately 10,000 although new flexible endoscopes carrying up to 50,000 fibers are being developed. Thus, the image quality of the flexible endoscope is still inadequate for pituitary surgery, and its use is limited to occasional inspection at deep curved anatomical regions. Three-mm or 4-mm rod-lens endoscopes can be used for primary visualization during pituitary surgery since they provide clear video images. Four-mm rod-lens endoscopes provide full-screen, high-quality images in contrast to the smaller, inferior quality images provided by 3-mm rod-lens endoscopes. The basic endoscopes used by the authors are 4-mm rod-lens endoscopes with 0-, 30-, or 70-degree lenses. As previously mentioned, the slender physical shape of the endoscope shaft with the visualizing lens at the tip allows navigation through a narrow anatomical space and eliminates the need to traumatically retract a straight tubular surgical corridor. Surgical incision, septal mucosal dissection, or removal of the nasal septum is unnecessary. Therefore, postoperative nasal packing is also not necessary. The occurrence or amount of postoperative bloody nasal discharge is very minimal, and postoperative comfort of the patient is related to the minimal anatomical disruption during surgery.

Surgical Procedure

Surgical Instruments

Appropriate surgical equipment is necessary to perform optimal endoscopic pituitary surgery. Attempting an endoscopic operation of this nature with a borrowed otolaryngologic endoscope can potentially result in frustration. Endoscopic surgical techniques are quite different from those of microscopic surgery. Being well-trained in microscopic surgery does not preclude the need for practice in endoscopy. The required surgical instruments are endoscopes with 0-, 30-, and 70-degree lenses (Fig. 22-4A) and their appendages, including a video-imaging system and light source connections, an endoscope lens-cleansing device, a rigid endoscope holder, and various other surgical instruments specifically designed for endoscopic pituitary surgery. The length of an endoscope must be 18 cm or longer. When an 18 cm-long endoscope was used for removal of a posterior fossa tumor through an endonasal transclival approach, it proved to be marginally short and restricted the surgeon’s operating space between the endoscopic appendages and the patient’s face. Fluoroscopic guidance, which was used in earlier patients, is no longer used in routine pituitary surgery. It is rarely but occasionally used for anterior or posterior cranial fossa surgery, and for pituitary tumor patients in which complexity of the sinonasal anatomy is anticipated.

FIGURE 22-4 The sinonasal endoscopes used for endonasal pituitary surgery are 4 mm in diameter and 18 cm in length with 0-degree, 30-degree angled-up or angled-down, and 70-degree angled-up or angled-down lenses (A). The tube with green top and black tip is the sheath of the Endoscope Lens Cleansing Device (Endoscrub®, Xomed-Treace, Bristol-Myers Squibb, Jacksonville, FL). The base of the battery-powered lens cleansing device (Endovision®, Karl Storz, Tuttlingen, Germany) is connected to the endoscope sheath and serves as a tool for cleaning the lens using foot pedal control (for forward irrigation of warm saline solution at the lens followed by brief reverse flow) without removing the endoscope from the surgical field (B).

An endoscopic lens-cleansing device is required to cleanse the lens so that the surgeon can operate without interruption (Fig. 22-4B). The device consists of a disposable irrigation tube, which has a loop of tubing passed through a battery-powered rotary device. The irrigation tube is connected into a warmed saline bag (the temperature prevents lens fogging), which is hung on a pole, and the motor-powered irrigation device is controlled by a foot pedal to flush saline forward. When the foot pedal is released, the motor reverses its rotary direction and draws the saline back for 1 to 2 seconds. The forward flow of irrigation saline cleans the lens, and the reverse flow clears water bubbles at the tip of the endoscope. Although this device is not yet perfect, it helps the surgeon significantly in the task of keeping the endoscope lens clean in order to preserve the optimal technical continuity and flow of the procedure.

Appropriate endoscope holders help provide stability of the visual image and bimanual instrument use during portions of the case during which this is optimal, such as drilling and the majority of tumor removal (Fig. 22-5). Although there are portions of surgery during which dynamic visualization is important, such as the initial approach to the sphenoid sinus rostrum and final visualization of any tumor remnants at anatomic corners of the sella, endoscope holders provide camera stability akin to a video camera tripod during appropriate segments of surgery and does not require the presence of a trained assistant to constantly drive or hold the endoscope camera. The endoscope holder should also provide rigid fixation of the endoscope while also allowing easy transition between stable fixation and manual dynamic steering. The holding terminal is necessarily compact and slender so as to render adequate operating space around the endoscope shaft for the surgeon to maneuver surgical instruments. We routinely use a customized manual endoscope holder specifically designed for EE-TS, in contrast to a nitrogen-powered holder called the Mitaka Point Setter (Mitaka USA; Park City, Utah) for our endoscopic transcranial approaches, and a nitrogen-powered holder called Unitrac (Aesculap; Tuttlingen, Germany) for our endoscopic spine surgery. Manual holders have multiple joints that are tightened by hand to set the final position, but only a single joint has to be loosened during a case to transition from endoscope fixation to manual driving or back. Manual holders are highly stable without significant constraints in range-of-motion or disadvantage of the settling phenomenon, but the configuration can purposefully be set such that the range-of-motion of the final joint is constrained to maintain the trajectory of the endonasal route for EE-TS and depth adjustments only require the simple untightening of a single joint. Nitrogen-powered holders are more expensive but conveniently provide release and tightening using a single button. The Mitaka Point Setter provides excellent stability and minimal settling phenomenon but is limited by the constrained range-of-motion to cases that require only minor maneuvering of the endoscope holder. The Unitrac is stable and highly maneuverable but displays significant settling phenomenon such that the final endoscope position sinks somewhat with gravity before locking in final position. Other endoscope holders are still in development to attempt to maximize the strengths and minimize the weaknesses of the various endoscope holders.

FIGURE 22-5 The customized manual endoscope holder consists of a custom-made distal joint in combination with a Greenberg retractor mounting system. The holder provides rigid fixation of the endoscope (akin to a video camera tripod) during specific portions of surgery such as drilling or tumor removal, to provide stable video images as well as bimanual capabilities for a lone surgeon to use surgical instruments. The holder is setup along a parallel trajectory with the surgical route to allow a smooth range of endoscope depth changes. The ergonomics of the customized holder also allows easy alternation between endoscope stabilization in the holder and single-handed endoscope steering as needed for dynamic surgical visualization or view adjustments during the operation.

Among various surgical instruments, a monopolar suction coagulator (No. 8 or 9 French cannula), a bipolar suction coagulator (No. 8 or 9 French cannula), and a single-bladed bipolar coagulator are useful tools for hemostasis. These are all disposable, and the monopolar suction coagulator is malleable and insulated. The malleable monopolar is useful in bloodless preparation of the nasal cavity for anterior sphenoidotomy. The bipolar suction coagulator and single-bladed bipolar coagulator have two cables for producing bipolar functioning, the single-bladed bipolar has one electrode at the core and the other at the shell. These bipolar instruments are used for dural or intradural hemostasis. Suction cannulas with variously curved tips (No. 5 and 7 French cannulas) are used for sellar operations. Titanium microclips have been used as a dural suturing device and nitinol U-clips are also commercially available, but further evolvement would be ideal for endoscopic dural suturing. Other instruments used include a micropituitary rongeur, pituitary rongeur, ethmoid rongeurs, high-speed drill, micro-Kerrison rongeurs, pituitary ring curettes, Jannetta 45-degree microdissector, single-bladed Kurze scissors, and a specially-designed septal breaker. A slender high-speed drill is useful when the sphenoid sinus is small and not well-pneumatized.

Myths in Sinonasal Surgery

In early patients, topical application of a vasoconstrictor and local infiltration of lidocaine with epinephrine were used with the belief that intraoperative and postoperative bleeding would be reduced. Sometimes a piece of polytetrafluoroethylene (Teflon) or Gelfoam sponge was also left at the middle meatus in the hope that it would minimize postoperative bleeding and mucosal adhesions. However, these ineffective practices were gradually eliminated from our technique as experience accumulated. When the topical use of a vasoconstrictor and local injection of lidocaine with epinephrine were completely eliminated, delayed postoperative nasal bleeding markedly decreased. The use of vasoconstrictors may lessen bleeding intraoperatively, but postoperative nasal bleeding was increased presumably due to inadequate intraoperative hemostasis during the active vasoconstriction phase and rebound vasodilatation when the vasoconstrictor effects wore off postoperatively. Meticulous hemostasis using monopolar coagulation (and bipolar coagulation if needed) at the rostrum of the sphenoid sinus without the masking effect of intraoperative vasoconstrictors is the key to minimizing the incidence of postoperative nasal bleeding. When we performed careful hemostasis at the rostrum mucosa and anterior sphenoidotomy site, the placement of a Teflon or Gelfoam sponge was also unnecessary.

When an anterior sphenoidotomy was performed, care is taken not to strip the mucosa at the sphenoid sinus. When the sphenoidal mucosa is stripped unnecessarily from the sinus cavity, not only can the resultant excessive bone bleeding interfere with surgery, but the healing of the sinus is nonphysiologic. When the bony opening of an anterior sphenoidotomy is made, only the focal corresponding mucosa at the anterior sphenoidotomy site is opened to enter the sphenoid sinus. Minimal mucosa at the anterior wall of the sella is removed using electrocoagulation with the remaining mucosa of the sphenoid sinus preserved. When pituitary tumor removal is completed, the anterior wall of the sella is reconstructed by folding the flaps of thin sellar bone back in place. The sphenoid sinus is left intact without any packing, and these precautions allow physiologic healing of the open sphenoid sinus with normal mucosal lining.

Since the nasal cavity cannot truly be conventionally prepared with extensive antiseptic solutions, we prescribed postoperative oral antibiotic regimens empirically for 5 days in our early patients. Subsequently, postoperative antibiotic treatment has been completely abandoned without any evidence of increased infection. We still swab the nasal cavity with an antiseptic solution during surgical preparation, but even this practice may not be clearly necessary.

Positioning

The patient is positioned supine with the torso elevated about 15 to 20 degrees, and the head is positioned with the forehead-chin line set horizontally. The level of the head is placed a little higher than that of the heart with the intent that the cavernous sinus venous pressure stays low to minimize venous bleeding. The horizontally leveled head positioning allows the surgeon to access the region of the middle turbinate easily and naturally for EE-TS when the endoscope is inserted at approximately 25 degrees cephalad.¹¹ When the anterior cranial fossa is to be explored as in EE-ACF, the head is extended approximately 15 degrees.¹⁹ Conversely, the head is flexed by 15 degrees when the clival or posterior fossa region is to be explored in EE-PFossa.²² The head is rotated toward the surgeon at 10 to 20 degrees. A head pin fixation device can optionally be used but is not necessary. The hip and knee joints are gently flexed for patient comfort, and a soft pillow is placed underneath the knee joints. A Foley catheter is not routinely used but is inserted occasionally in selective patients who are expected to undergo longer operating hours or for the possible anticipated occurrence of diabetes insipidus. Fluoroscopic C-arm imaging is not used except in patients with anterior fossa or posterior fossa tumors or in patients with complex sinonasal anatomy. Ophthalmic eye ointment is placed on the cornea and conjunctiva, and the eyelids are taped closed with double-layers of soft vinyl adhesives to prevent corneal abrasions and infiltration by prep solutions. The oropharynx is packed with a 2-inch gauze roll to prevent the accumulation of blood at the perilaryngeal area during surgery, which may cause aspiration at the time of extubation.

The video monitor is placed a few feet away from the patient’s head to face the surgeon directly. The lens-cleansing motor is placed next to the video monitor, and the scrub nurse is positioned adjacent to the surgeon. The entire face, nasal cavity, and abdominal wall are prepared and draped in an aseptic manner. When fat graft material is required to fill the tumor resection cavity, an appropriate amount of the abdominal fat tissue is obtained through a 1- to 2-cm infraumbilical transverse skin incision. Clindamycin is mixed with the endoscope’s irrigation fluid. For the intraoperative antibiotic regimen, 2 g cefazolin is given intravenously in the operating suite before the start of the operation.

Surgical Approaches

An endoscopic endonasal approach to the sella can be made by a paraseptal, middle meatal, or middle turbinectomy approach.^10,¹⁹ The paraseptal approach is the least invasive and basic workhorse among these three approaches, and the surgical technique described here for EE-TS involves the paraseptal approach. The paraseptal approach is made between the nasal septum and the middle turbinate with temporary displacement of the middle turbinate laterally and contralateral displacement of the posterior nasal septum by fracturing at the sphenoid rostrum. The fractured nasal septum is pushed away by submucosal dissection at the contralateral side of the sphenoid rostrum.

For endoscopic endonasal access to the anterior cranial fossa (EE-ACF), the paraseptal approach can be used between the nasal septum and middle turbinate with trajectory confirmed using fluoroscopic C-arm guidance or image-guidance systems. The middle meatal approach involves trajectory lateral to the middle turbinate and provides access to the ipsilateral anterior cranial fossa by an anterior ethmoidectomy or direct access to the anterior aspect of the cavernous sinus and optic nerve by a posterior ethmoidectomy. When a larger operating space is required, the middle turbinectomy approach can be used by resection of the middle turbinate. Although a wider corridor is provided to the sella, lack of the middle turbinate structure can be problematic when a supportive structure is required for skull base reconstruction.

Surgical Technique of Endoscopic Endonasal Trans-Sphenoidal Surgery

Positioning is done as previously mentioned with the patient’s head resting such that the forehead and chin make a straight line parallel to the floor. The head may also be turned and angled slightly such that endonasal access is in a comfortable positioning for the operating surgeon who stands on one side of the patient during surgery. Optionally, approximately 15-degree bends can also be made at the level of the waist and knees to allow a comfortable degree of flexion at the hip and knee joints. The ipsilateral arm on the side of the operating surgeon is tucked, and the contralateral arm may be on an armboard. The nasal cavities, face, and a small region on the abdomen in case a fat graft is needed (usually the infraumbilical area is used for cosmesis) are prepped and draped in an aseptic manner. Double-layer eye protection is used to shield from prep solution, with the nose left exposed in a triangular fashion. Multiple long-handled disposable cotton swabs (routinely a total of 10 with 5 per side) are used to prepare the nasal passages.

The base of the endoscope holder is attached to the head of the bed, then there are two holder arms that are attached at appropriate angles (such that the attachment is in parallel with the course expected through the nasal passage) before the distal portion of the holder is attached that directly affixes the endoscope. The patient’s head should be close to the top of the operating table but not so close that the endoscope holder runs into the head. As the nasal cavity is being prepared with the cotton swabs, the size of the nasal airway can be assessed to determine which nostril is to be used. The nasal septum is usually somewhat deviated to one side, and thus the nostril with the wider nasal airway can usually be selected for the surgical approach. The size of the nasal airway is also anticipated in advance by reviewing the axial view that includes the nasal cavity on preoperative MRI. When both nasal cavities are comparable in size, the nostril contralateral to the lesion is used in patients with microadenomas that are located laterally. Since the endonasal approach is a few degrees off from the midline, it is relatively easy to visualize the contralateral side of the sella and the cavernous sinus in the standard paraseptal approach.

The endoscopic endonasal trans-sphenoidal (EE-TS) procedure can now be thought of as four basic steps: manual endoscope navigation to the sphenoid sinus, opening of sphenoid and sella, tumor removal, and closure. As an overview, the initial step of endonasal navigation to the rostrum of the sphenoid sinus uses the pathway between the nasal septum medially and the middle turbinate laterally while steering the endoscope with one hand and using a suction in the other hand to help lead the endoscope under direct visualization (Fig. 22-6A). Once the target site of the sphenoid sinus rostrum is exposed, the endoscope can be placed in its holder and the drill is used in one hand with the suction in the other to make the anterior sphenoidotomy and to access the sellar target (Fig. 22-6B). When the anterior sphenoidotomy is complete, the endoscope can be adjusted to an optimal surgical position in the endoscope holder for sellar entry and tumor removal. Finally, after tumor removal, the sellar bone is replaced and the middle turbinate pushed back into position during closure of the operation.

FIGURE 22-6 Schematic drawing shows manual endoscopic navigation into the nasal cavity with one hand holding the endoscope and the other hand, a suction cannula or other surgical instrument (A). When bimanual surgical maneuvering is required, the endoscope is anchored to the endoscope holder (B).

The first part of EE-TS is done with the endoscope usually in the nondominant hand used to directly visualize a 7-French suction in the dominant hand that leads the endoscope into the nasal cavity. The inferior turbinate is often initially visualized, and then the inferior margin of the middle turbinate is followed to the posterior nasal cavity where the ipsilateral choana with the nasopharynx transition is located. Through the choana, the vertically-oriented ridges and valleys of the pharyngeal tonsils can be seen along with the auditory tube opening laterally. The endoscope and suction are backed out after confirming this relation between the middle turbinate and the choana, then the space between the middle turbinate and nasal septum is followed posteriorly to the sphenoid target.

When the endoscope is held in the hand, the palm and last three digits are generally used to stabilize the endoscope shaft, and the index finger and thumb are used to steer the video camera to maintain anatomic orientation of the video image. This endoscope grip will naturally keep the endoscope at a 25-degree incline and allows for continuous steering of the video camera for maintaining correct orientation of the video image. When the patient’s head is positioned horizontally with the forehead-chin line parallel to the floor, the middle turbinate is easily visualized at the tip of the endoscope when it is inserted into the nasal cavity. If the space between the nasal septum and middle turbinate is limited, several half- by three-inch cotton patties are inserted between the septum and middle turbinate to gently widen the space with minimal trauma (Fig. 22-7A and B). The cotton patties are pushed down to the rostrum of the sphenoid sinus. Care must be taken not to traumatize the mucosa in the nasal cavity while surgical instruments are being inserted and removed. The degree of surgical trauma to the nasal mucosa is a crucial factor in determining the amount of postoperative nasal bleeding. When a sharp-edged surgical instrument is inserted, the instrument tip must be guided by direct endoscopic visualization. The insertion of the surgical instrument should ideally be impelled by the gravity of the surgical instrument itself rather than surgeon’s mechanical push. If cotton patties are required to develop the middle turbinate-septal space, the cotton patties are removed after a few minutes and the developed space will remain, although there may be some mild mucosal bleeding. Mucosal bleeding from the rostrum of the sphenoid sinus in the middle turbinate-septal space is controlled with electrocoagulation using the malleable monopolar suction coagulator. The mucosa at the rostrum of the sphenoid sinus is visualized with the manual-driven endoscope and completely coagulated before being divided vertically approximately 1.5 cm in length rostrally from the level of the inferior margin of the middle turbinate. The posterior septal artery arises from the sphenopalatine artery and passes at the inferolateral corner of the sphenoethmoidal recess, which is approximately the posteromedial corner of the inferior margin of the middle turbinate. The posterior septal artery must often be coagulated and divided to prevent intraoperative and postoperative nasal bleeding. The site for an anterior sphenoidotomy is again confirmed with reference to the surgical landmarks, which are the inferior margin of the middle turbinate and the choana of the nasopharynx (Fig. 22-8).

FIGURE 22-7 Under the 0-degree endoscope, the right-sided middle turbinate is exposed at the center of the surgical field (A). When the space between the nasal septum and middle turbinate (mt) is limited, several 0.5-by-3-inch cotton patties are inserted between the middle turbinate and the nasal septum anterior to the rostrum of the sphenoid sinus (B).

FIGURE 22-8 Schematic drawings demonstrate the target area for the anterior sphenoidotomy. The inferior margin of the middle turbinate follows a trajectory leading posteriorly to an area approximately 1 cm inferior to the sellar floor, useful as a consistent surgical landmark.

The second part of EE-TS involves use of the customized endoscope holder, which is an L-shaped connection from the operating table that connects to a reverse L-shaped segment running parallel to the trajectory of the endonasal pathway and a distal clamp that holds the endoscope itself. The endoscope is placed back into the nasal cavity following the same originally established trajectory along the endoscope holder with the coagulated sphenoid rostrum target reidentified at the sphenoid sinus and vomer interface. The endoscope is fixed in the endoscope holder, and a 4 mm diamond drill bit is used to drill the posterior nasal septum at the vomer and sphenoid rostrum to allow displacement towards the contralateral side. The floor of the sphenoid sinus is drilled along with only the underlying focal portion of mucosa (with the remaining sphenoid sinus mucosa left intact). The floor of the sella turcica presents as a bulge or mound with the prominences of the carotid arteries and cavernous sinuses bilaterally visualized and correlated with any anticipated anatomic variations from the preoperative MRI. The prominences of the optic nerves, the opticocarotid recess (OCR), and the tuberculum sella are often anterior to the pituitary target location and may not necessarily need to be exposed. The malleable coated suction monopolar is turned down to a setting of 10V (from 25V used for mucosal coagulation at the outer face of the sphenoid sinus during the first part of EE-TS) and the bipolar is routinely set at 35V (with adjustment as needed for any intradural use). The anterior sphenoidotomy to be made ranges from the inferior margin of the middle turbinate to the sphenoid sinus ostia, which is typically about 1 to 1.5 cm rostral from the inferior margin of the middle turbinate. However, the plane of the inferior margin of the middle turbinate is the consistent anatomic landmark. Although the sphenoid sinus ostia may be visualized directly (Fig. 22-9A), its identification is not necessary for performing an anterior sphenoidotomy. When the sphenoid sinus is entered near the level of the inferior margin of the middle turbinate, any further rostral exposure can be easily made relative to the exposed sellar floor. When an anterior sphenoidotomy is first attempted rostrally, the surgeon may erroneously enter the anterior cranial fossa because the superior turbinate can sometimes mimic the middle turbinate. Therefore, the middle turbinate must be confirmed in reference to the choana of the nasopharynx. The inferior margin of the middle turbinate is located just rostral to roof of the choana at the nasopharynx in a sagittal plane. Following the inferior margin of the middle turbinate posteriorly then leads to the clival indentation at approximately 1 cm inferior to the level of the sellar floor.

FIGURE 22-9 Cotton patties can be placed to create gentle expansion of the space between the middle turbinate and nasal septum, with the rostrum of the sphenoid sinus visualized upon removal of the patties. When mucosal bleeding is encountered, selective electrocoagulation is performed with monopolar suction cannula at the focal bleeding points. Sometimes the sphenoid ostium may be visible (double arrows), but can be a variable landmark (A). An anterior sphenoidotomy measuring approximately 1.5 to 2 cm in diameter is made using a high-speed drill or Kerrison and ethmoidal rongeurs. When the endoscope is advanced into the sphenoid sinus, a panoramic view (B) demonstrates the clival indentation (CI), internal carotid arteries (C), sella (S), cavernous sinuses (CS), planum sphenoidale (PS), and optic protuberances (O).

Using a bipolar suction coagulator, the sphenoidal mucosa at the anterior wall of the sella is coagulated and removed. The suction is used to nudge the sellar floor and discern the thickness of the sellar bone via tactile feedback. A small entry hole is made at the inferolateral corner of the anterior bony wall of the sella by using either the drill for thick sella or a 1-mm Kerrison rongeur to gently punch through thin sella. The anterior bony wall of the sella is then removed with a 1-mm Kerrison punch circumferentially, from one cavernous sinus to the other cavernous sinus, and from the sellar floor to the tuberculum sella. When the sellar bone has adequate thickness, the anterior bone wall can be opened like a door with the hinge attached at the sellar floor or tuberculum sella. The sellar bone may be opened in an H-shaped flap with superior and inferior halves or as a single inverted-U flap. At the end of operation, the bony door can simply be closed for sellar reconstruction. The dura mater is coagulated along the periphery circumferentially with a single-bladed bipolar coagulator. The dural opening is made along the inferior margin at the floor of the sella using a Jannetta 45-degree microdissector. The anterior dural wall is incised and removed circumferentially for biopsy. Alternative option is an X- or cross-shaped incision of the dura mater.

The third part of EE-TS involves tumor removal with the identification of tumor tissue versus normal pituitary, and ring curettes are used to remove tumor along with pituitary forceps used to send specimens for frozen pathology sections as needed. Once all of the tumor tissue is removed, a very thin rim of normal pituitary gland is removed for margin. Tumor tissue is often soft and white, in contrast to firm orange-yellow anterior pituitary gland and firm white posterior pituitary gland. For larger pituitary tumors, classically the posterior portion of the tumor is removed first, followed by both lateral borders, and then the anterior portion of the tumor is allowed to fall down into the center of the field by gravity assistance if amenable. Otherwise ring curettes can simply be used to remove tumor tissue appropriate for the individual tumor configuration as needed.

In the case of a microadenoma covered by normal pituitary tissue, the pituitary tissue is sliced or split with a Jannetta 45-degree microdissector to locate the tumor tissue. The identified tumor tissue is removed by curettage; a thin layer of the normal pituitary tissue is then shaved-off at the margin of the resection site, especially to optimize the chance of endocrine cure for functional microadenomas. For macroadenomas, the tumor tissue often spills out when the dura mater is opened. Care has to be taken not to lose the tumor specimen by suctioning since the tumor tissue should be sampled for pathologic examination. Once enough of the tumor specimen is collected, the tumor is removed with a suction cannula at the central portion of the sella for debulking. A pituitary ring curette in one hand with suction in the other hand or dual suction cannulas (No. 5 or 7 French) can be used for soft tumor removal. When the tumor is fibrotic, either from previous medical and surgical treatments or by its intrinsic nature, the tumor tissue is gently curetted with a pituitary ring curette held in one hand, in addition to being suctioned with a suction cannula held in the other hand. When the tumor resection cavity is created at the central portion of the pituitary fossa, a 45-degree angled curette is first used followed by a 90-degree angled curette to remove the lower portion of the tumor from the floor of the sella. An inferiorly angled pituitary ring curette is used in one hand and an inferiorly curved suction cannula in the other hand for removal of the lower portion of the tumor. The dura mater at the floor of the sella is exposed directly when the lower portion of the tumor is removed. Next the lateral portion of the tumor is removed with a superiorly angled suction cannula and a superiorly angled pituitary ring curette, 45-degrees as well as 90-degrees. The medial wall of the cavernous sinus is directly exposed when the lateral portion of the tumor is removed. The rostral portion of the tumor is removed circumferentially with various superiorly curved and angled suction cannulas and pituitary ring curettes. When normal pituitary gland tissue is identified, it is preserved as much as possible. When the diaphragm sella is identified along the peripheral edge of the rostral portion of the tumor, the tumor is continuously removed circumferentially. When the tumor is removed along the edge of the diaphragma sella, the suprasellar portion of the tumor progressively descends through the central opening of the diaphragma sella. The suprasellar portion of the tumor that progressively descends is continuously removed with either two superiorly curved suction cannulas or a suction cannula and a pituitary ring curette, both angled superiorly.

Thinned pituitary tissue is often identifiable rostrally when the suprasellar portion of the tumor has been removed. When the pituitary tissue is severely stretched-out, the rostrally located pituitary tissue appears to be a transparent membrane similar to the arachnoid membrane. When this rostral tissue is penetrated, the arachnoid membrane may rupture, resulting in a cerebrospinal fluid (CSF) leak. Sometimes the arachnoid membrane bulges down along the anterior edge of the diaphragma sella in front of the thinned pituitary tissue. The last piece of the pituitary tumor is often located at the insertion point of the pituitary stalk. When this last piece of the tumor is removed at the reversed dimple of the pituitary stalk, the transparent and thinned pituitary tissue descends down, looking much like a lily with a dimple at the center. It continuously bulges downward with pulsation towards the floor of the sella. When the tumor resection cavity in the sella is large and the remaining tissue is very thin, the tumor resection cavity may have to be filled and supported with an abdominal fat graft in order to prevent postoperative CSF leak due to delayed rupture of this thin membrane. Delayed CSF leak can occur from unintentional Valsalva maneuvers produced by repeated coughs, bearing-down during extubation, or at anytime postoperatively.

When the tumor is so solid and fibrotic that the suprasellar portion of the tumor does not descend spontaneously, the suprasellar portion can be exposed directly using a 30-degree lens endoscope or by further removal of the bone at the planum sphenoidale or tuberculum sella. When the arachnoid membrane is ruptured, the optic nerves and chiasm, anterior cerebral artery system, and inferior aspect of the hypothalamus are under direct view with a 30-degree lens endoscope. When CSF leakage does not occur intraoperatively and the tumor is a microadenoma, an abdominal fat graft is unnecessary. After removal of a large macroadenoma, the tumor resection cavity is supported with an abdominal fat graft (Fig. 22-10A to F). Occasionally a piece of Gelfoam sponge is used instead of an abdominal fat graft when a sufficient amount of the pituitary tissue still remains rostrally. An abdominal fat graft is harvested using a 1- to 2-cm transverse skin incision just inferior to the umbilicus. The anterior wall of the sella is reconstructed using autogenous bone saved at the time of the anterior sphenoidotomy (Fig. 22-11A). When autogenous bone is not available, a piece of thin titanium mesh is placed (Fig. 22-11B). No foreign material is placed in the sphenoid sinus or nasal cavity.

FIGURE 22-10 A 53-year-old man presented with visual deficits and panhypopituitarism associated with a large nonfunctioning pituitary adenoma demonstrated on T1-weighted MRI with contrast, coronal and sagittal views (A, B). Postoperative photos of the patient at the recovery room (C) and following morning just before his discharge from the hospital (D) reflect his uncomplicated recovery from EE-TS surgery. Postoperative T1-weighted MRI with contrast, coronal and sagittal views (E, F), demonstrate total tumor removal with fat graft (F) at the sella.

FIGURE 22-11 A small piece of abdominal fat graft is placed at the tumor resection cavity when the void is relatively large or cerebrospinal fluid leakage is encountered intraoperatively. The anterior wall of the sella is reconstructed with autogenous bone (A) or titanium mesh (B).

So the fourth and final part of EE-TS consists of closure and cleanup. The reconstruction of the sella in routine EE-TS involves replacement of the sellar bone flaps as previously mentioned. The endoscope is removed from the holder to be manipulated by hand again, the nasopharynx and nasal cavity are inspected and cleaned, and any stagnant blood is removed with a suction cannula. The middle turbinate is placed back to its normal position using a Cottle dissector-elevator. If a fat graft was used, the abdominal incision is closed in subcuticular fashion and covered with a small bandage to complete the operation.

Endoscopic Endonasal Approach to the Anterior Cranial Fossa

For meningiomas located in the olfactory groove, planum sphenoidale, or tuberculum sella and for repair of CSF leakage at the anterior cranial fossa, the endoscopic endonasal approach to the anterior cranial fossa skull base (EE-ACF) has been employed (Fig. 22-12A).^16,^17,¹⁹ This approach is also useful for suprasellar craniopharyngiomas or large suprasellar pituitary tumors with fibrotic solid consistency. For tumor removal, a paraseptal approach is used (Fig. 22-12B). For CSF leak repair, either a paraseptal or a middle meatal approach can be used. Fluoroscopic C-arm imaging or frameless stereotactic image-guidance system can be used for optimizing the trajectory to the target lesion during EE-ACF.

FIGURE 22-12 Schematic drawing (A) demonstrates an endoscopic approach to the anterior skull base. The paraseptal approach is the routine technique, although this can be extended to a middle turbinectomy approach to provide wider surgical space in selected cases as necessary (B).

The head is positioned in 15-degree extension of the forehead-chin line to maintain the endoscope insertion angle at about 25 degrees, which is naturally comfortable for the surgeon and follows the basic endonasal pathway. Otherwise the patient is prepared in the same manner as described earlier for EE-TS pituitary surgery. For the middle meatal approach, the middle turbinate is pushed medially and an ethmoidectomy is performed to reach the anterior skull base. Any CSF leak is often directly visible. The mucosa is dissected around the skull base defect, and an abdominal fat graft is inserted into the cranial cavity. After the entire fat graft is inserted into the cranial cavity, a portion of the fat is grabbed and pulled gently to wedge it into the skull defect in a dumbbell-shaped or snowman-shaped configuration. A piece of thin titanium mesh is then placed at the skull defect. The middle turbinate is placed back gently in its normal position.

For EE-ACF tumor surgery, a paraseptal approach is often used. For tumors located at the olfactory groove, planum sphenoidale, or tuberculum sella, the surgical approach is similar to the aforementioned EE-TS pituitary operation except that further rostral exposure is required. The middle turbinate is laterally displaced, and the nasal septum is fractured contralaterally. A rostral anterior sphenoidotomy is performed to enter the sphenoid sinuses, and then the sella and tuberculum sella are identified. Under fluoroscopic guidance, further rostral exposure is made at the anterior skull base removing the posterior ethmoid sinuses. This approach itself interrupts anterior or posterior ethmoidal arteries during exposure, resulting in major devascularization of the meningioma. Approximately a 2-cm wide portion of the midline anterior skull base can be exposed with this technique. Bone of the skull base can be removed with a high-speed drill or Kerrison punch. The dura mater is opened, and the tumor is removed with central debulking followed by peripheral dissection. When the central portion of the tumor is excised, peripheral dissection is carried out to inspect the posterior aspect of the tumor. The remaining tumor is gradually flipped, and dissection along the posterior wall of the tumor is carried out until the remaining tumor is excised (Fig. 22-13A to D). Prudent selection of meningiomas should be considered for EE-ACF approaches versus transcranial approaches (whether minimally invasive endoscopic or open microscopic) because the inability to achieve at least a Simpson grade 2 resection due to inadequate exposure may result in suboptimal recurrence rates.

FIGURE 22-13 T1-weighted MRI with contrast, coronal and sagittal views (A, B), shows an anterior cranial fossa meningioma involving the planum sphenoidale and tuberculum sella in a 34-year-old woman. Intraoperative endoscopic photos demonstrate the meningioma, which was dissected and gently rotated towards the patient’s right side in order to visualize the posterior anatomy, with the left optic nerve revealed (C). The anterior cerebral arterial complex, optic system, and pituitary stalk are displayed by view through a 0-degree-lens endoscope following tumor removal (D).

The main potential problem related to this surgery is postoperative CSF leak and subsequent meningitis. Therefore adequate skull base reconstruction is essential. When active CSF leak is noted at the time of surgery, a small piece of fat graft is inserted at the various corners intracranially in order to obstruct the active CSF inflow. Then a large dural graft is placed intradurally with enough margin overlapping, dural suture is performed with titanium clips, and another layer of dural graft is laid extradurally. There are other similar methods of dural graft reconstruction described such as composing the double-layer graft with a central suture prior to placement at the skull base defect or using alternative methods of dural suturing such as nitinol U-clips. The skull base defect reconstruction is then supported with autogenous bone graft or titanium mesh placement. Abdominal fat grafts are used at the ethmoidectomy site as additional support (Fig. 22-14A to C). When fat graft material is placed at the tumor resection cavity, care must be given not to cause unintended compression to the optic nerve system. Nasoseptal flaps have been reported but may not be routinely necessary depending on the skull base defect. The middle turbinate is placed back in its normal position to complete the operation.

FIGURE 22-14 T1-weighted MRI with contrast, coronal views, preoperatively illustrates an olfactory groove meningioma (A), which was removed with an endoscopic endonasal approach, and postoperatively shows appearance of the skull base reconstruction (B). The skull defect is most commonly reconstructed with double-layered dural graft supported by titanium mesh, followed by abdominal fat graft placement at the ethmoidectomy area. Endoscopic view under a 0-degree-lens demonstrates the anterior cerebral arterial complex, lamina terminalis, and optic system (C).

Endoscopic Endonasal Approach to the Optic Nerve or Cavernous Sinus

Although surgical indication for decompression of the optic nerve is a controversial issue, the optic nerve at the optic canal can be easily exposed using this endoscopic endonasal approach.¹³ The surgical approach to the cavernous sinus is similar to that of the optic nerve.^14,^15,^20,²¹ This endoscopic approach to the cavernous sinus is best suited for pituitary adenomas invading the cavernous sinus. Biopsy for the histologic diagnosis of cavernous sinus lesions can be performed with this technique. Tough fibrotic tumors in this region, such as some types of meningiomas, can be challenging to remove using endoscopic technique. The endoscopic endonasal cavernous sinus (EE-CS) procedure is an anteromedial approach, and the fact that cavernous cranial nerves are located towards the lateral wall of the cavernous sinus makes this approach advantageous.

Pituitary adenomas can involve the cavernous sinus by mechanical compression with lateral tumor bulging, by direct extension via dural infiltration, or by intrusion into the cavernous sinus through a defect of the medial wall of the cavernous sinus. A laterally bulged tumor can be removed by the pituitary approach described earlier and does not need any further particular maneuvering. The 30-degree lens endoscope discloses the medial wall of the cavernous sinus well when the lateral portion of the tumor is completely removed. Tumors that have intruded into the cavernous sinus by a defect of the medial wall can be removed completely under direct endoscopic visualization. The cavernous carotid artery is exposed during this procedure. Invasive pituitary adenomas of an infiltrating nature may not be completely resectable; however, they can be debulked to reduce the size of the tumor so that focused beam radiation treatment can be performed for the residual portion of the tumor postoperatively.

The optic nerves or cavernous sinuses can generally be approached through a paraseptal approach, with increasing exposure as needed by creating a middle meatal approach or even further exposure by using a middle turbinectomy approach.¹⁵ In the paraseptal approach, the endoscope visualizes the contralateral optic nerve or cavernous sinus better than it does the ipsilateral one, and this technique exposes the anteromedial aspect of the cavernous sinus (Fig. 22-15A). The anteromedial exposure of the optic nerve or cavernous sinus through the contralateral nostril using the paraseptal approach is similar to that of the previously described EE-TS for pituitary adenomas except that the trajectory is adjusted by entry through the contralateral nasal passage from the lesion. The middle meatal approach with a posterior ethmoidectomy provides a straight anterior approach to the cavernous sinus (Fig. 22-15B). The largest corridor to the optic nerve or cavernous sinus is provided by the middle turbinectomy approach, but overall the paraseptal approach is generally sufficient for approaching the optic nerve or cavernous sinus for the majority of lesions.

FIGURE 22-15 Schematic drawing indicates surgical exposure at the medial aspect of the cavernous sinus when surgical approach is made via a paraseptal approach through the contralateral nostril (A). However, when a middle meatal approach is made to the cavernous sinus through the ipsilateral nostril, a straight anterior view will be noted at the cavernous sinus with the possibility of access lateral to the cavernous carotid artery using an appropriate trajectory (B).

During the anterior sphenoidotomy, submucosal dissection at the contralateral side of the sphenoid rostrum is extended further laterally, and the anterior sphenoidotomy can be performed generously at the contralateral side of the sphenoid sinus. This exposes the contralateral cavernous sinus laterally up to the medial anterior temporal fossa. The bone is removed from the anterior aspect of the sella as well as from the cavernous sinus, and unroofing the internal carotid artery may be completed if necessary. The sellar portion of the pituitary tumor is removed first before attacking the portion of tumor in the cavernous sinus. For an isolated cavernous sinus tumor, the tumor is approached directly by opening the dura mater medial to the carotid siphon (Fig. 22-16A and B). The tumor is removed with various pituitary ring curettes and suction cannulas. Attention must be taken during tumor removal not to traumatize the lateral wall of the cavernous sinus since this can cause ocular cranial nerve dysfunction. The carotid artery pulsation is directly visible, and tumor resection is performed medially and posteriorly to the carotid siphon, which arcs in a C-shape for the patient’s right carotid artery or a reverse C-shape for the left carotid artery with the convexity directed anterolaterally. When the tumor is completely removed, the lateral wall of the cavernous sinus can be completely visualized (Fig. 22-17A to C). The cavernous carotid artery is surrounded using an abdominal fat graft to protect the artery postoperatively. If necessary, the sphenoid sinus can additionally be filled with an abdominal fat graft for further protection of the exposed carotid artery. In contrast with pituitary surgery, the sphenoid sinus mucosa should be removed completely before the fat graft is placed in this case.

FIGURE 22-16 Endoscopic view under a 0-degree lens via the right-sided nostril discloses a pituitary adenoma (tu) at the left-sided cavernous sinus in a patient with acromegaly (A). After total tumor removal, the lateral wall (lw) of the cavernous sinus and carotid artery (ca) are exposed (B). The patient normalized IGF-1 levels postoperatively.

FIGURE 22-17 Preoperative T1-weighted MRI with contrast, coronal view, shows a recurrent nonfunctioning pituitary adenoma with extension to the left cavernous sinus (A). Postoperative T1-weighted MRI with contrast, coronal view, demonstrates total tumor removal via EE-TS (B). Intraoperative photo demonstrates a 30-degree-lens endoscopic view at the lateral wall of the left-sided cavernous sinus after total tumor removal (C). CA, carotid artery; LW, lateral wall of the cavernous sinus.

Endoscopic Endonasal Approach to the Pterygoid Fossa or Petrous Apex

Tumors involving the pterygoid fossa can be approached with a middle meatal or middle turbinectomy approach. The posteromedial wall of the maxillary sinus can be removed if necessary, and then the pterygoid fossa is fully exposed. The vidian nerve or sphenopalatine ganglion in the pterygoid fossa can also be approached with this technique. The petrous apex can be approached with a paraseptal approach. This endoscopic endonasal approach is particularly useful for drainage of cholesterol granulomas. Approach through the contralateral nostril gives a bit more lateral angulation in the trajectory to the petrous apex. When the sphenoid sinus is entered, the sellar floor and carotid artery protuberance provide anatomical orientation, and a stereotactic image-guidance device may assist with further anatomical orientation. The internal carotid artery is exposed at the medial margin, and the petrous apex is approached through the clivus inferior to the sellar floor and medial to the paraclival segment of the cavernous carotid. When the cholesterol granuloma is entered, xanthochromic fluid and material can be drained (Fig. 22-18A to D). Placement of fat graft material over the carotid artery for arterial protection is not necessary unless the aforementioned segment of the carotid artery is fully exposed by the exposure. Once the cholesterol granuloma is drained, the operation is complete.

FIGURE 22-18 T1-weighted MRI with contrast, axial view, reveals a cholesterol granuloma at the left petrous tip in a 47-year-old man with 1-year history of left-sided partial sixth cranial nerve palsy (A). EE-Petrous approach was performed with drainage of the lesion, and T1-weighted MRI with contrast, axial view, demonstrates reduction of the cholesterol granuloma (B). Postoperative photographs demonstrate complete recovery of the left sixth cranial nerve palsy (C, D), and no recrudescence of the cholesterol granuloma has occurred in 7 years of follow-up.

Endoscopic Endonasal Approach to the Clivus or Posterior Fossa

The advantage of the endoscopic technique in the endonasal surgical approach to the clivus and posterior fossa (EE-PFossa) is the flexibility and range of endoscopic visualization, which spans from the crista galli at the anterior cranial fossa to the foramen magnum at the posterior cranial fossa.^22,²³ This endoscopic approach exposes the entire clivus from the floor of the sella to the foramen magnum at a midline width of approximately 2 cm (Fig. 22-19), with the internal carotid arteries serving as the lateral limits of this exposure. This technique has been used for the radical resection of clival chordomas and midline clival meningiomas. A paraseptal approach is most commonly used, but the middle turbinectomy approach can be used when a larger surgical corridor is required. Fluoroscopic C-arm imaging or frameless stereotactic system is used for guidance to the vertical dimension. The clival bone is removed with a high-speed drill between the internal carotid arteries in the transverse dimension and from the floor of the sella to the foramen magnum or to the lower clival level as needed. The chordoma is then removed with suction cannulas and pituitary rongeurs. Bone is shaved at the tumor resection margin until normal bone is clearly documented. Intradural tumor is then resected, during which the pons and medulla can be visualized (Fig. 22-20A to D and Fig. 22-21A to C). A 30- or 70-degree lens endoscope visualizes the further rostral aspect of the brain stem or cranial nerves laterally (Fig. 22-22A and B). Dural defects are repaired with an abdominal fat graft, but once appropriate surgical instruments are fully developed, direct repair by a dural graft will be the ideal method for reconstruction. The dural titanium microclip applicator is currently available but is too short to be used effectively for this purpose.

FIGURE 22-19 Schematic drawing demonstrates endoscopic approach to the clivus and craniocervical junction. Approximately a 2-cm midline window between the carotid arteries can be opened. Clival tumors or midline posterior fossa lesions can be approached with this technique.

FIGURE 22-20 Preoperative T1-weighted MRI with contrast, axial and sagittal views, displays a large clival tumor with brainstem compression in a 28-year-old man with bilateral partial sixth cranial nerve palsies (A, B). Postoperative T1-weighted MRI with contrast, axial and sagittal views, shows total tumor removal of the clival chordoma by endoscopic endonasal approach (C, D).

FIGURE 22-21 Intraoperative photo displays the appearance of the basilar artery and brain stem after removal of the clival chordoma shown on MRI in Fig. 22-20A. The 28-year-old male patient recovered bilateral sixth cranial nerve palsies completely within 1 year (B, C).

FIGURE 22-22 A 70-degree-lens endoscope discloses a chordoma encasing the basilar artery in another patient with a large clival chordoma (A). When the tumor was removed, the basilar bifurcation, III nerves, and mamillary bodies are visualized (B).

Endoscopic Endonasal Approach to the Craniocervical Junction (EE-CC Junction)

This endoscopic endonasal approach provides simple access to the craniocervical junction and the C1–C2 (atlanto-axial) area.¹⁸ Pathologies such as chordoma, os odontoidum, basilar impression or invagination, rheumatoid basilar settling, or anterior lesions compressing the ventral aspect of the cervicomedullary junction can be approached with these techniques. Lateral fluoroscopic guidance or stereotactic image guidance can assist to access the surgical target. It can be done through one nostril or two nostrils. Under the endoscopic visualization, the nasopharyngeal mucosa and posterior pharyngeal muscles are incised at the midline with electrocoagulation. The clivus at the ventral foramen magnum and the C1–C2 area can be exposed as indicated, and the clivus at the ventral foramen magnum, anterior rim of the C1, and odontoid can be drilled to the tectorial membrane. The dura mater can be exposed by incising the tectorial membrane. Lateral image using fluoroscopic guidance or frameless strereotactic image-guidance can help indicate the extent of surgical exposure. Additional posterior fusion surgery is necessary when stabilizing structures such as the C1 anterior arch and the transverse ligament are traversed to access the lesion. When the odontoid tip protrudes rostrally beyond the upper edge of C1 anterior arch, the protruding portion of the odontoid can sometimes be removed without removing the ventral C1 rim. In that case, C1–C2 stability can be preserved.