Transcranial Surgery for Pituitary Macroadenomas

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Chapter 23 Transcranial Surgery for Pituitary Macroadenomas

Pablo F. Recinos, C. Rory Goodwin, Henry Brem, Alfredo Quiñones-Hinojosa

The most common tumors affecting the suprasellar, intrasellar, or parasellar region include pituitary adenomas, craniopharyngiomas, meningiomas, germ cell tumors, and gliomas involving the hypothalamus or optic chiasm. Management is dictated according to each specific diagnosis. While medical therapies can be utilized in a subset of patients, many lesions require surgical management, which is most commonly carried out using a trans-sphenoidal approach. Sellar and suprasellar tumors are characteristically treated via a trans-sphenoidal approach because these operations are less invasive, provide direct access to the tumor with preservation of normal pituitary tissue, and have a quicker recovery of vision and visual field defects due to minimal manipulation of the optic nerves and chiasm. Despite the advantages of the trans-sphenoidal approach, certain pituitary tumors cannot be completely resected via the trans-sphenoidal approach and require transcranial surgery.

Transcranial approaches are used in approximately 1% to 4% of pituitary tumors that require surgical management.^1,² The most common indications for transcranial surgery for pituitary tumors are large extrasellar tumor extension without sellar enlargement, marked frontal, middle fossa, or clival extension of tumors (particularly dumbbell shaped), very fibrous tumors not amenable to trans-sphenoidal resection (meningiomas), a persistent visual field deficit after incomplete decompression via the trans-sphenoidal approach, a coexistent aneurysm, loss of oculomotor function, ectatic midline carotid arteries, or sphenoid sinusitis.¹^–³ Treatment selection depends on the tumor characteristics and its associated findings. A thorough understanding of the advantages and disadvantages of each transcranial approach is critical when choosing the most appropriate surgical option.

History

In 1893, Caton and Paul recorded the first attempted, but unsuccessful, pituitary tumor resection using a two-stage lateral subtemporal decompression in a patient with acromegaly.⁴ This approach was suggested by Sir Victor Horsley, who from 1904 to 1906, used a subfrontal approach and a lateral middle fossa approach to operate on 10 patients with pituitary tumors.⁵ In comparison to the 50% to 80% mortality rate of his colleagues, Horsley reported a mortality rate of 20% using this approach. In 1904, Kilani showed an extensive bifrontal intradural approach using cadavers.⁶ In 1905, Krause demonstrated that it was possible to reach the sella turcica via a frontal transcranial approach in a living patient.⁷ In 1912, McArthur described an extradural approach via resection of the supraorbital ridge and orbital plate.⁸ These approaches formed the basic foundation upon which subsequent neurosurgeons improved and modified surgical treatment of these pathologies.^8,⁹

Harvey Cushing played a central role in standardizing the preference for transcranial surgery over the trans-sphenoidal approach. Cushing’s initial experience with transcranial approaches to sellar neoplasms was very discouraging and as such, he adopted the trans-sphenoidal approach that was undergoing marked improvement at the time.¹⁰ Cushing had a mortality rate of 5.6% in his series of 231 patients from 1910 to 1925 who had undergone surgical resection via the trans-sphenoidal approach.¹¹ The morbidity and mortality associated with the trans-sphenoidal approach at the time were primarily attributed to infection, most often associated with postoperative cerebrospinal fluid (CSF) leak, postoperative edema, and hemorrhage.⁹ These complications coupled with Cushing’s extreme interest in intracranial surgery prompted the development of a novel transcranial approach to sellar-based neoplasms. Cushing’s increased experience with transcranial procedures, and subsequently the reduced mortality he experienced utilizing these approaches, led to a preferential treatment of sellar tumors using an intracranial approach.⁹ The transfrontal craniotomy, performed via a direct midline approach, allowed Cushing to attain a more extensive resection, better visualization and decompression of the optic nerve and chiasm, lower recurrence rates, and better recovery of vision.^9,¹² The transfrontal approach also avoided the potentially fatal complication of infection seen with the trans-sphenoidal approach. For these reasons, Cushing discarded the trans-sphenoidal operation, and with his prominence in American neurosurgery, he helped to usher in a strong preference for the transfrontal approach.^11,^13,¹⁴

From the 1930s to the 1950s, transcranial approaches to the pituitary dominated neurosurgical practice and teaching. In the late 1950s and 1960s, the trans-sphenoidal procedure received renewed interest as many technological and surgical advances improved this surgical approach including: (1) development of a lighted speculum retractor by Dott in 1956,¹⁵ (2) enhanced surgical accuracy with the intraoperative radiofluoroscopy to define nasal passage anatomy and control the position of the instruments by Guiot,¹⁶ (3) development of antibiotics in the 1950s to reduce the surgical mortality associated with this approach,¹⁷ and (4) introduction of corticosteroids allowing safer surgeries to be performed on the pituitary gland.¹² Some of these advances were utilized by Hardy in 1971 in his landmark paper that demonstrated the trans-sphenoidal operation on over 300 patients undergoing hypophysectomy.¹⁸ In his paper, he described the technical aspects of the trans-sphenoidal hypophysectomy and also reported a morbidity and mortality rate that was less than with transcranial approaches. Specifically, the risk of CSF leak was markedly reduced when the arachnoid was left intact. Since then, trans-sphenoidal surgery has dominated neurosurgical treatment of sellar-based lesions.

Specific Indications

While the trans-sphenoidal approach is standard for resection of sellar/parasellar region tumors, there are specific indications for transcranial approaches. The usual reason for using a transcranial approach is doubt about the diagnosis.¹⁹ For instance, if the lesion is not a pituitary adenoma, but instead perhaps a meningioma or craniopharyngioma, a craniotomy is advised because these lesions are more safely removed transcranially.¹⁹ For tumors with a wide extension on the cranial base, craniotomy remains a superior approach. Craniotomy is more effective in a variety of other surgical cases as well because it increases access to tumors, facilitates preservation of the surrounding neurovascular structures, improves visualization at the dural edge, and allows earlier identification of the cranial nerves and the feeding vessels.²⁰

Failed Trans-Sphenoidal Surgery

A major indication for a transcranial procedure is a failed trans-sphenoidal surgery. Failure can occur for multiple different reasons. Any intrinsic tumor characteristic that does not allow it to fall into the sella compromises the efficacy of trans-sphenoidal surgery. For instance, if a pituitary adenoma is too fibrous, a trans-sphenoidal approach will fail. In those circumstances, it is advisable to take no more than a biopsy specimen and obliterate the sphenoid sinus. The latter action may seem unnecessary with a large tough tumor between the nasal cavity and the CSF. The consistency of the tumor, not the size, limits the effectiveness of trans-sphenoidal surgery.¹⁹

Failure of the suprasellar extension to descend is another reason for failed trans-sphenoidal surgery. The usual cause is that a component of the tumor is extending superiorly, laterally, or anteriorly. If the suprasellar extension has pushed vertically, it usually falls into the tumor cavity created by the trans-sphenoidal surgeon. If an extension of tumor hooks around the optic nerve or carotid artery, this extension prevents descent of the tumor, and the tumor extension above the carotid artery or chiasm is inaccessible.¹⁹ The anterior extension is particularly troublesome for the trans-sphenoidal surgeon because it is at the wrong angle for the line of approach.¹⁹ In addition, recurrent pituitary adenomas may not fall down satisfactorily because of adhesions between the tumor and the surrounding brain. In these circumstances, the combined transcranial/trans-sphenoidal approach may be the best method to completely remove the tumor. Thus, it may be justified if the tumor has recurred despite previous irradiation. Radical surgery is also indicated for hormone-secreting adenomas such as those that occur in patients with acromegaly (or Cushing syndrome), in which hormonal cure depends on total removal of the tumor.¹⁹ A trans-sphenoidal procedure is also insufficient when the surgery fails to remove adequate amounts of tumor, particularly enough to decompress the optic chiasm.^19,²¹ The failure often manifests after incomplete decompression as a persistent visual field deficit or persistent loss of vision.

Para/Extrasellar Extension

In cases with large extrasellar tumor extension without sellar enlargement, the pituitary gland may be vulnerable to a trans-sphenoidal approach. Usually in this case, the suprasellar component either encases optic nerves or intracranial arteries or it spreads over the surface of the planum sphenoidale.²¹

Also, pituitary adenomas can invade one or both cavernous sinuses. While the trans-sphenoidal approach is limited to the compartment of the cavernous sinus medial to the C4 segment of the internal carotid artery, this approach can be used in patients with non-secreting adenomas in which tumor debulking and neurovascular decompression is sufficient.²¹ Transcranial approaches are warranted, however, if the adenoma is secretory, or if the parasellar extension ventures beyond the cavernous sinus into the middle fossa.²¹ Transcranial approaches are also indicated when restoration of oculomotor function is the goal.

Dumbbell-shaped pituitary adenomas that have a ‘narrow’ waist created by a thick diaphragm sellae and a small pituitary stalk opening warrant a transcranial approach over a trans-sphenoidal. One can predict the failure of trans-sphenoidal surgery for a dumbbell shaped lesion based on tumor compression into the sella by intraoperative lumbar intrathecal injection of sterile saline and endoscopic navigation of the opening in the diaphragm sellae.²¹

Other

Co-existent aneurysms, ectatic carotid arteries, and severe sinus infection are indications for transcranial surgery. Aneurysms are found concomitantly in approximately 1.1% of all pituitary adenoma cases.^21,²² If an aneurysm adjacent to a pituitary adenoma (i.e. an aneurysm of the anterior cerebral artery) is detected preoperatively, both lesions can be potentially treated in the same operation. Co-treatment of these lesions is more applicable when an aneurysm will be affected by manipulation of the regional anatomy.²¹ Alternative treatment strategies include a staged-procedure, surveillance of either lesion or nonsurgical treatments such as endovascular coiling for the aneurysm and radiotherapy for the pituitary adenoma.²¹ In terms of ectatic vessels, the tumor’s relationship to the intercavernous carotid arteries should be taken into account when deciding on an appropriate approach. There is commonly a 1 to 3 mm separation between the medial margin of the internal cerebral arteries and the lateral surface of the pituitary gland.²³ Ectatic carotid arteries can veer into the midline trajectory preventing a trans-sphenoidal approach.⁹ Also, if a sinus infection is severe and surgical delay will pose a threat of acute neurological deterioration, a transcranial approach is warranted.^20,²¹

Diagnosis and Workup

The preoperative work-up for patients with signs or symptoms of a sellar neoplasm should include formal testing of the patient’s visual fields and pituitary function. A T1-weighted magnetic resonance imaging (MRI) scan with and without gadolinium in the sagittal and coronal planes should also be performed to allow proper visualization of the optic nerves, optic chiasm, carotid arteries, cavernous sinuses and surrounding soft tissue.^19,²⁴ A T2-weighted scan may be useful in determining the fibrotic nature of a tumor in this region to aid in surgical planning. Although no reliable predictor exists, evidence suggests that pituitary adenomas with a homogeneously isointense, as opposed to hypertense, signal on T2-weighted MRI are predicted to be firm and fibrotic, although this is not routinely used radiologic criteria.^20,^21,²⁵

The position of the optic chiasm can be predicted on the sagittal MRI scan by finding the anterior communicating artery.¹⁹ While the length of the intracranial optic nerves varies from patient to patient, tumor extension influences the distance of the optic nerves to the tuberculum sella. If the suprasellar extension is thrust between the optic nerves, it pushes the chiasm upward and backward, allowing good surgical access. On occasion the suprasellar extension pushes the chiasm upward and forward, severely limiting surgical access.¹⁹ This is called a “prefixed chiasm.”

Craniotomy for tumors in this region carries the same general risks as any operation (i.e., deep vein thrombosis, bleeding, infection, anesthetic risks), however there are specific risks associated such as damage to the optic nerves (resulting in impaired vision or visual fields), damage to the internal carotid artery or anterior cerebral artery, and damage to the pituitary stalk (resulting in hypopituitarism and diabetes insipidus).¹⁹ The transcranial approach almost inevitably causes hypopituitarism because the normal pituitary tissue is pushed superiorly under the diaphragm sella, and this tissue is specifically coagulated and cut by the surgeon en route to the tumor.¹⁹ The potential for harm to the vascular structures in this area necessitates cross-matching of 2 pints of blood. Anticonvulsants should be started preoperatively because epilepsy is possible after transcranial surgery. Cerebrospinal fluid rhinorrhea or anosmia can occasionally occur, especially if excessive retraction of the frontal lobe is indicated.¹⁹

Aims of Surgery

The aims of pituitary surgery are ultimately to cure the patient of the tumor, without damage to the pituitary; to relieve the symptoms and the signs that have been caused by the tumor; and to achieve this relief without damage to the patient. When the tumor is secreting hormone, total extirpation of the tumor is necessary to achieve a cure. A nonfunctioning tumor does not necessarily require total removal, especially if the risks of such an attempt are significant. In these circumstances, the aims should be an adequate debulking of the tumor to produce chiasmal and optic nerve decompression before radiotherapy or radiosurgery.

Pterional

The frontosphenotemporal or pterional craniotomy is the most commonly used transcranial approach to pituitary tumors (Fig. 23-1). It was popularized by Yaşargil as an approach to intracranial aneurysms and is now the most widely used transcranial approach in neurosurgery.²⁶^–²⁸ It provides a direct path to the sella turcica and allows removal of large pituitary tumors with minimal brain retraction. It should also be the transcranial approach of choice for tumors when a prefixed chiasm is present as the tumor can be resected safely underneath the optic chiasm.²⁷

FIGURE 23-1 Pterionial approach. A, Artist representation of patient positioning and skin incision. B, Preoperative coronal T1-magnetic resonance image of a multicystic pituitary adenoma with lateral extension. C, Postoperative MRI demonstrating total tumor removal via a left pterional approach. D, Intraoperative photo of the myofascial flap reflected anteriorly and inferiorly. E, Intraoperative photo of a semicircular dural flap reflected anteriorly with dissection of arachnoid adhesions anchored to the dura. (Adapted from Brotchi J, Pirotte B. Sphenoid wing meningiomas. In: Sekhar LN, Fessler RG, eds. Atlas of Neurosurgical Techniques, Brain. New York: Thieme Medical Publishers; 2006:628.)

Technique

A curvilinear incision is marked out. The caudal extent should start just below to the root of the zygomatic arch and 1 cm anterior to the tragus. The cranial extent depends on the patient’s hairline and should end either at the midline or at the contralateral mid-pupillary line. The scalp is dissected in two layers with the fascia of the superficial temporalis muscle left intact. The superficial temporal artery should be left intact to maintain the vascular supply of the flap and to serve as a possible bypass donor artery. The superficial scalp flap should be reflected until the superficial temporal fat pad is seen. A curvilinear incision is made in the temporalis fascia posterior to the fat pad. The fascia is dissected sharply from the temporalis muscle, which protects the frontalis branch of the facial nerve. Usage of the monopolar cautery should be avoided because it can result in thermal injury to the frontalis branch of the facial nerve. The superficial temporal fat pad and fascia are elevated by dissecting the insertion of the fascia from the superior aspect of the zygomatic body and frontozygomatic process. The fat pad is then reflected along with the superficial skin flap.

After reflecting the skin flap and fat pad, the temporalis muscle is elevated. An incision is made in the temporalis fascia 1.5 cm posterior to the frontozygomatic process and continued posteriorly along the linea temporalis. A 1- to 2-cm cuff is left attached to the linea temporalis for reattachment of the temporalis flap during closure.²⁹ Using subperiosteal dissection, the temporalis myofascial flap is elevated off of the skull.³⁰ Once the myofascial flap is completely reflected anteriorly and inferiorly, it is held in place using fish hooks.

The frontosphenotemporal craniotomy may be created using varying numbers of burr holes and either a standard router with the footplate attachment or with the Gigli saw. We prefer to make our craniotomy using two burr holes: (1) in the squamous portion of the temporal bone just superior to the root of zygoma and (2) at the MacCarty keyhole. The ideal location for the MacCarty keyhole burr hole is to create it on the frontosphenoid suture approximately 5 to 6 mm posterior to the junction of the frontozygomatic, the sphenozygomatic, and the frontosphenoid sutures.³¹ A Penfield #3 dissector is used to dissect the dura from the inner table.A standard router with footplate on a pneumatic drill is utilized to turn the craniotomy. The supraorbital foramen serves as the medial border of the craniotomy. Once the bone flap it ready to be elevated, it is important to free the dura that remains attached to the inner table with a Penfield #3 dissector.

After the bone flap is removed, extradural bony removal continues prior to opening the dura. The frontal and temporal dura are dissected off of the ridge of the sphenoid bone with a Penfield #1 dissector. The bony sphenoid ridge is removed using rongeurs. The sharp edges of bone may be smoothed out with a pneumatic drill with a #2 or #3 diamond bit. It is important to constantly irrigate the drill to prevent thermal injury to the dura and underlying optic nerve. The optic canal is skeletonized and the anterior clinoid process completely removed. The underlying clinoidal segment of the internal carotid artery is then visualized. When approaching tumors with wide parasellar extension or that encroach the cavernous sinus, uncovering the foramen rotundum and foramen ovale gives additional needed exposure to minimize temporal retraction.²⁶

Prior to opening the dura, cottonoids are then placed around the dural edges to wick the blood from the operative field. A semicircular dural flap is created and reflected anteriorly. Special care must be taken to dissect bridging veins and other adhesions anchored to the dura. Sutures are placed at the base of the dural flap and tied to the fish hooks retracting the temporalis flap to keep the dural flap under tension and out of the operative field.

The Sylvian fissure is split using a Nauta knife (18-gauge needle attached to 1cc tuberculin syringe). The extent of the dissection will be dependent on the size and extent of the tumor. Self-retractors may be placed on the frontal and temporal lobes with care to avoid excessive temporal lobe retraction. Placing moist telfa strips underneath the retractors provides an additional protective layer to the brain. Once the tumor is exposed, it is resected in a piece-meal fashion. The Cavitron ultrasonic aspirator is useful in coring out large, firm tumors. The tumor edges and capsule should be resected using bipolar cautery, microscissors, and suction in order to maintain direct visualization of critical adjacent structures.

Reconstruction of the one-piece bone flap is done using titanium burr-hole covers and plates to reattach the bone flap to the skull. The bone flap is preferentially situated as anterior as for an improved cosmetic result. Bone gaps that result from the osteotomies can be filled in with bone cement (such as CranioFix2^®) or covered with molded titanium plates. After the bony reconstruction is completed, the temporalis muscle is reapproximated to the myofascial cuff. The galea and skin flap are then closed in standard fashion.

Orbitozygomatic Craniotomy

The orbitozygomatic craniotomy is a second option in the treatment of sellar masses that have significant extension (Fig. 23-2). It arose from the supraorbital craniotomy first described by Jane et al. and evolved into an approach incorporating the orbitozygomatic and pterional cranial segments as described by Pellerin et al. and Hakuba and colleagues.³²^–³⁴ This approach provides a greater degree of exposure with reduced brain retraction compared to the pterional approach. It is especially useful in approaching lesions with considerable superior extension, those that extend laterally into the cavernous sinus, and those with significant parasellar and interpeduncular involvement.²⁶ However, given that it is less commonly used than the pterional approach, familiarity with the technical nuances of the orbitozygomatic approach is critical to minimize the increased risks associated with removal of the orbital rim.

FIGURE 23-2 Orbitozygomatic approach. A, Artist rendering of anatomical dissection and frontosphenotemporal craniotomy. B, Artist rendering of orbitozygomatic osteotomies to release the superior orbital roof, lateral orbital wall, and zygoma. The bone flap is plated prior to making the cuts to ensure appropriate fit during reconstruction. C, Preoperative coronal T1-magnetic resonance with gadolinium demonstrating a pituitary tumor with significant superior extension and compression of the optic chiasm and third ventricle. D, Postoperative T1-MRI with gadolinium demonstrating tumor removal via an orbitozygomatic approach. E, Intraoperative photo with the tumor seen pushing up on the optic chiasm. F, Magnification of the intrachiasmatic space demonstrating the relationship of tumor to optic chiasm. (A and B, redrawn from Conway JE, Raza SM, Li K, McDermott MW, Quiñones-Hinojosa A. A surgical modification for performing orbitozygomatic osteotomies: technical note. Neurosurg Rev. 2010;33(4):491-500. Epub 2010 Jul 27.)

Technique

Planning, positioning, and initial flap creation are done according to the previous description for the pterional craniotomy. The temporalis dissection differs due to the need for inferior reflection of the temporalis muscle flap in order to gain additional bony exposure to perform the orbitozytomatic osteotomies. The incision in the temporalis muscle is made starting 2 cm posterior to the frontozygomatic process and carried posterior 1 cm below the superior temporal line. The incision is angled inferiorly and terminates at the root of the zygoma. The myofascial temporalis flap is then dissected using a fan periosteal elevator. The temporalis flap is then reflected inferiorly underneath the zygomatic process until the inferior orbital fissure is visualized. It is critical to have adequate exposure of the inferior orbital fissure since two of the osteotomies pass through it. The masseter can be detached from the inferior portion of the zygomatic process. Alternatively, the masseter can be left attached and simply reflected inferiorly after the osteotomies are made in order to reduce the risk of postoperative trismus.³⁵

Dissection of the orbital rim and periorbita is performed with a #1 Penfield elevator. The supraorbital nerve is dissected out easily if it runs through a notch or chipped out carefully with an osteotome if it runs through a foramen. Upon dissection of the periorbita, the anesthesiologist should be warned about the possible production of vagal responses. Care must be taken not to violate the periorbita in order to minimize postoperative swelling. Dissection continues until the inferior orbital fissure is completely exposed.

The first step is to create a frontosphenotemporal craniotomy as described above. The second step is to create the orbitozygomatic osteotomies to release the superior orbital roof, lateral orbital wall, and zygoma. These have been described using varying number of cuts and instruments (e.g., oscillating saw). We accomplish this by making five osteotomies and prefer to use a long router bit with footplate for all of the cuts. The footplate provides a protective barrier that protects the soft tissues of the orbit. The first cut separates zygomatic arch from the root of zygoma. Placement of a dog-bone plate on the zygomatic arch that incorporates the location of the first osteotomy prior to making such cut will facilitate the reconstruction. The second cut separates the frontozygomatic process from the body of the zygoma. To accomplish this, a small retractor is placed gently on the periorbita, exposing the inferior orbital fissure. The footplate is then placed in the anterolateral portion of the inferior orbital fissure to initiate the cut. The third cut separates the temporal process of the zygoma from the zygomatic body. The footplate is placed on the inferior portion of the temporal process of the zygoma and directed obliquely to meet the second cut. The fourth osteotomy cuts through the superior orbital rim and orbital roof. Retractors are again used to protect the orbital contents and the frontal dura. The footplate is placed inside the orbit and directed immediately lateral to the superior orbital notch, over the supraorbital rim, and guided toward the superior orbital fissure. At the posterior orbital rim, the craniotome is directed laterally until reaching the junction of the superior and lateral orbital walls. It is then guided down the lateral wall of the orbit. The fifth osteotomy connects the fourth cut with the posterolateral portion of the inferior orbital fissure. The footplate is placed in the inferior orbital fissure in the infratemporal fossa and directed superiorly to complete second portion of the orbitozygomatic craniotomy.

Violation of the frontal sinus can occur during the orbitozygomatic craniotomy. The frontal sinus size and relationship to the relevant anatomy on preoperative MRI and/or computed tomography (CT) can help predict this event. If violation of the frontal sinus occurs and the nasofrontal duct is present, the frontal sinus mucosa does not have to be exenterated. In this case, large pieces of Gelfoam soaked in antibiotic solution can be used to pack the sinus. Alternatively, the mucosa of the sinus can be exenterated by monopolar cauterization followed by drilling the inner bony surfaces with a diamond burr. A pericranial flap is then used to tack down to the dura inferiorly to serve as a protective barrier to prevent CSF leak.

Reconstruction of the two-piece craniotomy is done by attaching titanium plates to reattach the bone flaps. The bone flap is preferentially approximated anteriorly in order to prevent a CSF leak from the frontal sinus (if violation occurred) and for an improved cosmetic result. Bone gaps that result from the osteotomies can be filled in with bone cement (such as CranioFix2®) or covered with molded titanium plates. After the bony reconstruction is completed, the temporalis muscle is reapproximated to the myofascial cuff. The galea and skin flap are then closed in standard fashion.

Bifrontal and Extended Bifrontal

The bifrontal and extended bifrontal are third-line transcranial options to approach pituitary tumors. The original concept of a bifrontal craniotomy was described by Frazier in 1913 and subsequently applied and developed to correction of craniofacial abnormalities by Tessier and to approaching skull base tumors by Derome.³⁶^–³⁸ These approaches are useful for tumors with significant superior and two-sided lateral extension and for those tumors that involve the medial orbits, clivus, upper air sinuses, and third ventricle. Removal of the orbital bar in the extended bifrontal craniotomy provides wide exposure of the anterior skull base and allows extensive inferior-superior viewing with minimal brain retraction.

Technique

The bifrontal and bifrontal-extended approaches are options that can be used when a suprasellar tumor has significant superior, inferior, and/or lateral extension (Fig. 23-3). In the bifrontal extended approach the orbital bar is removed, which increases the inferior-to-superior mobility and allows generous bilateral exposure to the cavernous sinuses. Specifically, the orbital contents can be mobilized to widen the path of exposure. With the additional exposure afforded by removal of the orbital rim, the amount of retraction on the frontal lobes is minimized. However, these approaches are considered as secondary alternatives to the more commonly used pterional and orbitozygomatic approaches because the amount of exposure attained is rarely needed for resection of pituitary macroadenomas.

FIGURE 23-3 Bifrontal and extended bifrontal approaches. A, Artist representation of bifrontal and extended bifrontal approaches with removal of frontal bone flap and orbital bar, respectively. B, Artist representation demonstrating scalp reflection forward, and anatomical location of burr holes and craniotomy cuts. C, Preoperative sagittal nonenhanced T1-magnetic resonance image of a pituitary tumor with anterior extension. D, Postoperative MRI demonstrating total tumor removal via a bifrontal approach. E, Intraoperative photo of a pericranial flap elevated off of the superior temporal lines and based anteriorly on the supraorbital rim. F, Intraoperative photo of the extended bifrontal craniotomy with the orbital bar removed. (A and B, redrawn and modified from images by Michael McDermott, MD.)

The patient is positioned supine and placed in the Mayfield head clap. The pins are positioned posterior to the ears in the mastoid bone. The two-pin side should be rotated in a cranial-caudal direction so that it does not interfere with the opening or closing. The neck should be translated superiorly and flexed toward the chest without compressing the jugular veins. Care must be taken while draping to not place towels right above the eyebrow that cause compression on the orbit when the flap is rotated forward.

A standard bicoronal incision is planned and the hair is minimally shaved. The application of bupivicaine with epinephrine after the prep is applied is very useful for hemostasis during the opening. During the opening, great care must be taken to dissect the scalp in the subgaleal plane and to avoid damaging the pericranium. The scalp is reflected forward and retracted with fish hooks. A pericranial flap is elevated off of the superior temporal lines and based anteriorly on the supraorbital rim. The supraorbital nerves are then dissected out if they run through a groove or chipped out with an osteotome if they travel through a notch. The periorbita is dissected off the orbital rim and the pericranial flap is reflected past the nasofrontal suture. The temporalis muscles are dissected off of the superior temporal line bilaterally and reflected inferiorly.

The craniotomy is planned by marking eight burr hole drill points. Burr holes should be placed on each side of the superior sagittal sinus at the anterior and posterior extent of the bone flap, on the MacCarty keyholes bilaterally, and 2 cm below the superior temporal line at the posterior extent of the flap. Using the craniotome, the craniotomy is made saving the cuts across the sinus for last. During elevation of the bone flap, the dura mater is separated from the orbits but should not be dissected past the crista galli to avoid injury to the olfactory nerves.

In the extended bifrontal craniotomy, the orbital bar is removed by making five cuts. The long router bit with footplate attachment is used to make all cuts. The first cut is made at the frontozygomatic suture in a cranial to orbital direction. Using a malleable retractor to protect the orbit, the second cut extends from the lateral orbit to the nasion in a horizontal plane. This is repeated on the contralateral side. The final cut is made across the nasion connecting the medial extent of the second cuts on both sides. The orbital bar is then removed in one piece. The frontal sinus mucosa should be completely removed from the frontal sinus recesses to avoid the possibility of future mucocele development.

Depending on the extent of the tumor, a primarily intradural or extradural approach may be taken. Tumors with a large suprasellar extent and limited intrasellar/parasellar extension can be resected using a primarily intradural approach. However, tumors with significant parasellar and/or intrasellar extension may require a wider exposure by removing the additional bone of the skull base.

The superior sagittal sinus is suture ligated next to the crista galli and the falx is cut until its deep edge. Further dissection beginning with the olfactory tracts is performed under the microscope. The olfactory nerves should be covered during dissection to prevent dessication. They are then dissected from the pia-arachnoid surface of the frontal lobes. If additional removal of bone from the skull base is required, the olfactory nerves cannot be preserved. Sacrifice of the olfactory nerves allows separation of the dura from the cribriform plate and the crista galli. During dissection, a single silicon-covered brain retractor is utilized to minimize unnecessary, prolonged retraction.

Once the tumor is identified, any feeding vessels in the periphery may be coagulated. Debulking of the tumor helps to dissect the periphery of the tumor without placing significant retraction pressure on the frontal lobes. In cases of extensive skull base bone removal, the sphenoid is removed to expose the sphenoid sinus and superior turbinate. For tumors with significant inferior extension, the clivus may be drilled down while those with extension into the cavernous sinus may be approached by drilling the anterior clinoid process. For large tumors with significant mass effect posteriorly, the posterior margin must be dissected carefully off of the anterior cerebral arteries and anterior communicating artery.

After completion of the tumor resection, the dura is closed with 4-0 Nurolon sutures. The frontal sinus is packed with moist Gelfoam and fibrin glue applied. The pericranial flap is then reflected down over the frontal sinus to create an additional vascularized barrier to prevent CSF leak. The orbital rim is reconstructed by placing small, dog-bone titanium plates laterally, connecting the orbital rim and the zygoma, and medially, reattaching the orbital rim across the nasion. Burr-hole covers are applied over each burr hole and the frontal craniotomy flap reconstructed. The galea and skin flap are then closed in standard fashion.

Supraorbital (Keyhole)

The supraorbital (keyhole) craniotomy has been previously described to approach anterior and middle fossa lesions, and specifically sellar lesions ³⁹^–⁴³ (Fig. 23-4). The advantages of this approach are that it requires a smaller incision, a single burr hole, carries a lower risk of injury to neurovascular structures that supply the temporalis muscle, minimizes the need for excessive brain retraction, and results in excellent cosmetic outcomes.^40,⁴¹ Pituitary macroadenomas that are confined to the sellar or region or those with minimal parasellar extension can be approached using the supraorbital (keyhole) approach. A supraorbital approach is not appropriate for pituitary tumors with extreme parasellar extension as the exposure is too limited for these tumors.^40,⁴⁴ The presence of a large frontal sinus on preoperative imaging should discourage the use of this approach as well.⁴⁰ Overall, the selection of this approach will depend on the individual tumors and the surgeon’s comfort level given that it is not the standard craniotomy for pituitary macroadenomas.^40,⁴¹ See Chapter 35 for the technical description of the supraorbital (keyhole) craniotomy.

FIGURE 23-4 Supraorbital (keyhole) approach. A, Artist rendering of the skin incision and craniotomy. B, Anatomic dissection and exposure with single brain retractor placed under the frontal lobe C, Preoperative sagittal T1-magnetic resonance image of a pituitary tumor with minimal suprasellar extension. D, Postoperative MRI demonstrating tumor removal via a supraorbital approach. E, Intraoperative view of the optic chiasm F, Skin closure following surgery. (A and B, redrawn from Jallo GI, Bognár L. Eyebrow surgery: the supraciliary craniotomy: technical note. Neurosurgery. 2006;59[Suppl 1]:ONSE157-158.)

Radical Combined Transcranial and Trans-Sphenoidal Approach

Occasionally, it is necessary to aim for a complete radical removal of the tumor (e.g., when a tumor has recurred despite radiotherapy). In these circumstances, following complete removal of the suprasellar component, the tuberculum sella is drilled off between the optic nerves and the optic foramina. The sphenoid sinus is entered, allowing the mucosa to be displaced and the anterior wall of the pituitary fossa to be removed. Removal of the sellar component can be achieved under direct vision except for the ipsilateral intrasellar tumor, which is less visible. Alternatively, a separate trans-sphenoidal approach can be carried out; that has the advantage of better bilateral tumor exposure, but it also has the disadvantage of possibly failing to see remaining tumor superiorly. Whichever method the surgeon uses, particular care must be taken to achieve a tight CSF closure with obliteration of the sphenoid sinus.

The first is if a previous trans-sphenoidal operation has been performed and an inadequate obliteration of the sphenoid sinus has been achieved. Previous sections have alluded to the necessity to obliterate the sphenoid sinus during a trans-sphenoidal approach when a transcranial procedure is clearly going to be necessary in the future. This necessity exists even when no CSF is seen. Failure to do so means that CSF rhinorrhea is extremely likely to occur after the transcranial approach, because the dural lining of the pituitary fossa has been penetrated during the trans-sphenoidal approach. In these circumstances, fascia and fat may be introduced into the pituitary fossa transcranially, but it is not easy to obtain a watertight closure this way. The second circumstance in which CSF rhinorrhea may be seen is when bone is drilled away from the skull base, thus entering an extension of the sphenoid sinus. If recognized, a fat and fascia repair is necessary. Rhinorrhea usually ensues when such an occurrence has not been recognized.

Complications

Frontal Lobe Damage

Frontal lobe damage is perhaps the most common complication, although it is often unappreciated because its manifestations may be subtle. Frontal lobe damage is particularly likely to occur in the elderly, and is caused by excessive frontal lobe retraction. The elderly take longer to recover from this surgery than from trans-sphenoidal surgery. There may be subtle changes of memory, judgment (on a social or professional level), concentration, and personality. These changes can be minimized by gentle surgical technique and, especially, by minimal brain retraction. A pattie or cotton strip should always be placed between the brain and the retractor. The retractor should be moved often, and should be removed when it is not needed. Splitting the sylvian fissure to separate the frontal and temporal lobes also minimizes the amount of retraction. If there is evidence of an area of soft, blue brain at the end of the operation, the surgeon should beware: this area may represent hemorrhagic infarction, which often causes postoperative bleeding and deterioration. Such areas should be removed surgically before closing the dura.

Frontal Lobe Cyst Formation

Cystic enlargement of an area of frontal lobe damage, sufficient to act as a space-occupying lesion, may occur. Adams described one such case and speculated on the causal mechanism.^19,⁴⁵

Anosmia

Unilateral or bilateral anosmia often reflects the vigor of frontal lobe retraction. If there is a significant subfrontal extension of the pituitary tumor, anosmia is inevitable.

Perioperative Optic Nerve Damage

If an eye is blind preoperatively, it will not recover postoperatively. If vision is severely impaired preoperatively, it is also unlikely to recover. If an already-damaged optic nerve is manipulated at all, vision is likely to be lost altogether postoperatively. The patient should be thus warned.

The most vulnerable nerve is the ipsilateral optic nerve. The rule is not to touch or manipulate it, but this is rarely possible to achieve. Before teasing tumor away, the tumor should be debulked as much as possible; only at the last stage, when space has been created, should the remaining tumor be rolled away from the optic nerve. Meningiomas creep down the optic foramen, but in the authors’ experience, pituitary tumors do not behave in that fashion.

The blood supply of the optic nerves and chiasm varies. The chiasm is supplied by small vessels from the anterior communicating artery, and these must be preserved. The rule is not to coagulate or cut any significant-looking vessel running to the chiasm or optic nerves. In general, however, it is suspected that manipulation of these structures, rather than ischemia, that usually causes the damage.

Damage to Internal Carotid, Anterior Cerebral, or Anterior Communicating Arteries

The previous author of this chapter described the unpleasant occasion of cutting an internal carotid artery.¹⁹ The patient was elderly, had undergone two previous craniotomies and radiotherapy for the pituitary tumor, and the artery was embedded in scar tissue. Although the artery was not visible, it should have been traced proximally from the middle cerebral artery. This tracing can be extremely difficult. On another occasion, he described damaging both anterior cerebral arteries. The tumor was firmly adherent to these vessels, and in hindsight the author stated he should have stopped the operation, leaving tumor behind around the vessels.

The literature describes such vascular damage repaired by fine sutures. Placing aneurysm clips so as to occlude the hole in the vessel without occluding the vessel has occasionally worked; usually, however, the vessel has to be occluded to stop the bleeding.

Occasionally a small vessel is pulled out of the side of a larger vessel. It can be difficult to stop the bleeding, but by placing the finest bipolar forceps on either side of the hole and using low bipolar coagulation, the hole is sealed without occluding the main vessel.

Hypothalamic Damage

Hypothalamic damage is rare after removal of a pituitary adenoma, but it is easily caused by overenthusiastic removal of a craniopharyngioma. With hypothalamic damage, the patient loses the senses of thirst and hunger. Fluid control can be achieved only by weighing the patient, and excessive weight gain is usual. Hypothalamic wasting or precocious puberty occurs in the presence of tumors (usually hypothalamic gliomas) and not after surgical trauma. To remove or not to remove a craniopharyngioma intimately involved in the hypothalamus demands the finest surgical judgment to balance the desire to achieve a total removal with the need to avoid devastating hypothalamic damage.

Pituitary Damage, Including Diabetes Insipidus

Damage to anterior pituitary function is common after transfrontal surgery because the normal pituitary gland is usually pushed superiorly against the diaphragma sella, rather like a rind around the tumor. The diaphragma is the first thing to be coagulated and cut when removing such tumor transcranially, hence destroying normal function. Pituitary hormone replacement therapy maintains reasonable health, but the patient never returns to normal. The patient seems sluggish, both physically and mentally, and gains weight. The standard hormone replacement therapy does not include growth hormone or other hormones given in the physiologically pulsatile fashion.

Fluids should be restricted to 2 l/day for 48 hours postoperatively. A postoperative diuresis is normal, especially in patients cured of acromegaly. If the urinary output is more than 200 ml/hr for 3 hours, plasma and urinary osmolalities are measured. If the former is increased and the latter is less than 295 mOsm/kg, desmopressin should be administered. The osmolality measurements should be repeated in 24 hours.

Salt-Wasting Syndrome

Salt-wasting syndrome is rare. The syndrome is also alarming, and usually occurs 1 to 2 weeks after the operation.⁴^–⁷ Surgeons have described their patients developing a headache, rapidly lapsing into a coma, and on admission presenting with a low sodium value. The mechanism is unknown, but salt-wasting syndrome is assumed to be caused by inappropriate antidiuretic hormone secretion. It is difficult to measure antidiuretic hormone, and so not enough is known about this rare condition. It is advisable to place a central venous line to determine if the problem is primarily low sodium (low venous pressure) or water overload (high venous pressure). Patients should be treated empirically with rapid infusions of fluids and salt, then restricted fluids to increase the serum sodium. Until more is known about this mysterious condition, it can be treated only empirically. Kelly and colleagues⁴⁶ recommend using urea for salt-wasting syndrome, pointing out that urea enhances sodium reabsorption at the kidney.

Postoperative Visual Deterioration

Acute visual deterioration within hours of surgery is usually caused by a postoperative hematoma in the tumor cavity. The best way to avoid this situation is to be sure to remove the tumor in its entirety. If, however, the tumor invades the clivus, bleeding from the cancellous bone can be difficult to stop, although bone wax, Surgicel, and patience are usually sufficient. Reoperation is necessary.

Olson and co-workers ⁴⁷ have described acute deterioration after trans-sphenoidal surgery resulting from herniation of a chiasm into the pituitary fossa. This condition is amazingly rare, considering how, after trans-sphenoidal surgery, the diaphragma rapidly descends to the floor of the pituitary fossa on many occasions without visual impairment. The question can be asked if herniation per se (apart from the case reported by Olson and co-workers) can cause visual deterioration.

Occasionally, a unilateral loss of vision occurs about 8 days after surgery. Morello and Frera ⁴⁸ describe a patient, and the author agrees with their conclusion that ischemic damage is the most likely explanation. Insidious visual deterioration is almost always caused by recurrent tumor, which usually reproduces the original visual field deficit (i.e., a bitemporal hemianopia). Another possibility is radiation damage to the optic nerves or chiasm after radiotherapy. This visual deterioration usually occurs 9 to 18 months after radiotherapy and is often sudden and unilateral. The mechanism is vascular damage and hence similar to stroke. Some improvement may occur. Guy and colleagues⁴⁹ suggest gadolinium-enhanced MRI scanning to confirm the diagnosis of radiation damage.

Key References

Couldwell W.T. Transsphenoidal and transcranial surgery for pituitary adenomas. J Neurooncol. 2004;69:237-256.

Couldwell W.T., Simard M.F., Weiss M.H., Norton J.A. Pituitary and adrenal. In: Schwartz S.I., Shires G.T., Spencer F.C. Principles of Surgery. 7th ed. New York: McGraw-Hill; 1999:1613-1658.

Czirjak S., Szeifert G.T. Surgical experience with frontolateral keyhole craniotomy through a superciliary skin incision. Neurosurgery. 2001;48:145-149. discussion 9-50

Day J.D. Surgical approaches to suprasellar and parasellar tumors. Neurosurg Clin North Am. 2003;14:109-122.

Derome P. Transbasal approach to tumors invading the skull base. In: Schmidek H., Sweet W. Operative Neurosurgical Techniques Indications, Methods, and Results. 4th ed. Philadelphia: WB Saunders Company; 1993:427-441.

Frazier C. An approach to the hypophysis through the anterior cranial fossa. Ann Surg. 1913;7:145-150.

Hakuba A., Liu S., Nishimura S. The orbitozygomatic infratemporal approach: a new surgical technique. Surgical Neurol. 1986;26:271-276.

Hayashi N., Hirashima Y., Kurimoto M., et al. One-piece pedunculated frontotemporal orbitozygomatic craniotomy by creation of a subperiosteal tunnel beneath the temporal muscle: technical note. Neurosurgery. 2002;51:1520-1523. discussion 1523-1524

Henderson W.R. The pituitary adenomata. A follow-up study of the surgical results in 338 cases (Dr. Harvey Cushing’s series). Br J Surg. 1939;26:811-921.

Jallo G.I., Bognar L. Eyebrow surgery: the supraciliary craniotomy: technical note. Neurosurgery. 2006;59:ONSE157-ONSE158. discussion ONSE-8

Jallo G.I., Suk I., Bognar L. A superciliary approach for anterior cranial fossa lesions in children. Technical note. J Neurosurg. 2005;103:88-93.