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.

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