Use of Endoscopes in Skull Base Surgery

Endoscopic endonasal approach to the central skull base. The divergent light of an endoscope placed in one nostril illuminates a broad area of the anterior and central skull base. Straight and angled endoscopes permit access to the frontal sinus, cribriform plate, ethmoid roof, sphenoid sinus, planum sphenoidale, sella, pituitary gland, suprasellar region, cavernous sinuses, dorsum sella, and midclival regions. This facilitates repair of encephaloceles and removal of tumors such as esthesioneuroblastomas, meningiomas, pituitary tumors, and clival chordomas.
Binarial endoscopic technique. Use of both nares permits bimanual dissection. For lesions accessed through the sphenoid sinus, the endoscope is best held by one surgeon superiorly in one nostril. This leaves ample room for the second surgeon to use two dissecting instruments, one in each nostril.
Middle turbinate removal. Sufficient access to the sphenoid sinus can usually be achieved by lateral displacement of the middle turbinate and superior turbinate on each side. The turbinates should be preserved whenever possible. However, a hypertrophic middle turbinate on the side to which the septum is deviated (right shown) may need to be resected. After its mucosa is injected with epinephrine and lidocaine to reduce bleeding, the turbinate is divided near its root and removed.
Sphenoidotomy. The ostium of the sphenoid sinus is found within the sphenoethmoid recess, bound medially by the posterior nasal septum and laterally by the superior turbinate. The posterior third of the nasal septum (the osseous perpendicular plate of the ethmoid) is removed with a back-biting rongeur and its mucosa is trimmed with a suction-debrider. Each ostium (right shown) is then enlarged toward the midline (dashed line) to connect with the contralateral sphenoidotomy. This removes much of the sphenoid rostrum. The opening of the sphenoid sinus is further enlarged by drilling away the central and lateral rostrum down to its base.
Sellar face. This wide sphenoidotomy provides sufficient space for manipulating the endoscope and two dissecting instruments through wide arcs without their impeding one another. This permits removal of any septations within the sphenoid sinus and visualization of its roof (planum sphenoidale), posterior wall (tuberculum sella, sellar face, and middle clivus), and each lateral wall (covering the intracavernous internal carotid artery and intracanalicular optic nerve). Bone removal begins over the anterior sella dura (lower dashed rectangle, blue); this can be extended laterally (over each cavernous sinus), superiorly (removing the tuberculum sella, bone over the medial optic-carotid recess, optic canals, and planum sphenoidale (upper dashed rectangle, green), and inferiorly (across the sella floor and down the midclivus).
Completed exposure of the pituitary gland and optic chiasm.
Clival chordoma: anterior posterior view. This chordoma of the sphenoid sinus, dorsum sella and midclivus elevates the pituitary gland and displaces the midbrain and pons posteriorly. Access to tumor behind the gland can be achieved by removing tumor anterior and then inferior to the gland and then elevating the gland.
Clival chordoma: axial view.
Clival chordoma: sagittal view.
Transsphenoid approach to the midclivus. After a standard endonasal approach, a wide sphenoidotomy exposes tumor in the sphenoid sinus, the sella above the tumor, the tuberculum sellae, and the planum sphenoidale. Removal of superficial tumor provides access to the remaining sellar face and floor.
Opening through the sella and planum. The sellar face and floor are removed with a drill and bone punches. Bone removal is continued laterally over the anterior faces of the cavernous sinuses. The tuberculum sella and the posterior aspect of the planum sphenoidale are also removed. Dura is incised transversely above and below the superior intercavernous sinus. The sinus is coagulated and excised. Anterior sellar and suprasellar dura are widely opened to expose the pituitary gland and the suprasellar cistern. The diaphragma sella can then be cut from its anterior edge to its hiatus to expose the distal pituitary stalk.
Removal of retrosellar tumor (dashed line). The pituitary gland is elevated out of the sella to access tumor of the dorsum sella. Division of the diaphragma sella anterior to the stalk and of adhesions of the gland to the dura of the sellar floor and the medial walls of both cavernous sinuses permits rotation of the gland superiorly to expose tumor involving the dorsum sella. Attenuated clival and dorsum sella dura is opened as needed to remove tumor. Often tumor infiltrates and transgresses the dura but the arachnoid of the prepontine cistern remains intact.
Esthesioneuroblastoma: anterior posterior view. A similar strategy permits removal of tumors of the anterior skull base such as esthesioneuroblastoma. This large tumor eroding through the cribriform plate and extending into the anterior cranial fossa and frontal sinus can be resected by an endoscope and instruments directed anterior and superior.
Esthesioneuroblastoma: axial view.
Esthesioneuroblastoma: sagittal view.
Initial nasal endoscopy. The tumor is seen emerging from the olfactory cleft region, displacing the anterior aspect of the middle turbinate laterally. A 0-degree endoscope is utilized for the initial visualization; as the dissection continues superiorly, 30- and 45-degree scopes provide optimal visualization.
Ethmoidectomy. Tumor exposure is gained by endoscopic excision of the middle turbinate and the anterior ethmoid air cells. Removal of these structures allows mobilization of the tumor to visualize its skull base origins and attachments.
Tumor resection. After delineation of the extent of the tumor, sequential piecemeal resection of the tumor is performed. Resection can be performed with a combination of through-cutting forceps, suction debrider, and bipolar cautery. Skeletonization of the ethmoid roof and cribriform plate region will reveal the origins of the tumor.
The sites of attachment to skull base and dura must be carefully surveyed, and in these areas generous surgical margins should be ascertained. Intraoperative frozen section biopsies may be helpful to assess adequacy of margins.
Dural and skull base repair. After removal of any intradural tumor, the dura is repaired with a dural substitute placed intradurally and extradurally. The bony skull base defect may be repaired using a prosthetic absorbable plate or a septal bone graft harvested through a septoplasty incision. The plate or bone graft is fixed by wedging its corners deep to the bone margins (inset). The bony repair is then covered by an additional layer of mucosa, via either a pedicled flap or free graft of nasal mucosa. Bio-compatible adhesive can help to secure the closure of any cerebrospinal fluid (CSF) fistula. The nose is then packed with an expansile sponge. If a substantial CSF fistula was created, a lumbar drain will be placed.
Pituitary microadenoma: anterior posterior view. Small pituitary tumors can be completely removed with little risk of pituitary injury or cerebrospinal fluid fistula. This typical 5-mm-diameter microadenoma lies inferior within the central portion of the gland. Even thought the tumor is small, the sphenoid must be opened widely to provide sufficient access for the endoscope and two dissecting instruments.
Pituitary microadenoma: axial view.
Pituitary microadenoma: sagittal view.
Sella opening and durotomy. After its opening with a diamond tipped drill or small chisel, bone of the face of the sella is removed with a small foot-plated punch from the superior intercavernous sinus above to the sella floor below and from one cavernous sinus to the other. Anterior sella dura is opened in rectangular fashion (dashed line). The corners of the rectangle are then coagulated with angled tipped bipolar forceps. This fuses the two layers of dura together, lest their separation open into a cavernous sinus. The durotomy is extended by lateral cuts into each corner.
Dural reflections and inspection. Peripheral reflection of the dural remnants exposes the entire anterior surface of the gland. Gentle displacement of the gland permits inspection of its surfaces against the dura of the sellar floor inferiorly, the diaphragma sella, and distal pituitary stalk superiorly, and the medial walls of the cavernous sinuses laterally. Detection of a small tumor (dashed line) may require incision into the gland.
Microadenoma removal. After incision of the gland over the tumor, the tumor is enucleated with fine dissectors. The tumor’s soft consistency and white-gray-purple color are usually distinguishable from the firm texture and orange hue of surrounding anterior lobe.
Resection of the pseudocapsule. The compressed layer of anterior lobe surrounding tumor may harbor tumor cells that can preclude endocrinologic cure or give rise to a recurrent tumor. Resection of this thin rim of pseudocapsule can accomplish a complete microscopic removal without impairing gland function.
Closure of the sella. After removal of the tumor and its pseudocapsule, both hemostasis and absence of a cerebrospinal fluid fistula are confirmed. The sella floor is reconstructed by placing a malleable plate of absorbable polyethylene glycol either intradurally or extradurally with its corners (dashed line) beneath the edges of the remaining bone. This is then covered by biocompatible or tissue adhesive. A free mucosal graft harvested from the floor of the nose may also be placed across the sellar defect to provide an additional layer of closure. Packing of the sphenoid sinus with fat or the nose with expansile sponge is not necessary.
Macroadenoma: anterior posterior view. Large tumors often expand the sella inferiorly and laterally, compress or invade the cavernous sinuses, and extend into the suprasellar space where they accordion the hypophyseal stalk and compress the optic chiasm. Enlargement of the sella and midline suprasellar extension with a smooth dome rather than a multilobulated superior surface are favorable for removal of the tumor by the transsphenoidal route. A normal-sized sella predominantly filled with pituitary gland, extension lateral to the intracavernous or supraclinoid internal carotid artery, and an irregular superior surface enmeshed in branches of the anterior cerebral artery are contraindications to this approach.
Macroadenoma: axial view.
Macroadenoma: sagittal view.
Removal of a macroadenoma. The approach to a larger tumor is similar to that of a microadenoma except for more extensive removal of bone over the cavernous and superior intercavernous sinuses. This permits lateral and superior reflection of these sinuses, respectively, for better visualization of tumor along the medial walls of the cavernous sinus and in the suprasellar cistern. First, the central mass of the tumor is reduced by suction or ring curettage.
Tumor is then removed from the sella floor and then up along the medial walls of the cavernous sinuses. Often, tumor that appeared to be within the cavernous sinus on preoperative imaging is found to have displaced a distended but intact medial wall laterally and thus can be removed without opening into the cavernous sinus.
After the sellar portion of the tumor has been removed, suprasellar tumor descends into the sella. This reveals a plane between the tumor and remaining gland, which often forms a crescentic pseudocapsule pushed superior and to one side. Careful dissection along this plane encourages further descent of the tumor dome without creating a cerebrospinal fluid fistula through remnant gland or through arachnoid that caps the tumor where gland does not. Failure of the evaginated gland and arachnoid to invert as a smooth surface invaginating into the sella indicates retention of tumor fragments within their folds. Apposed folds should be separated and these tumor fragments removed.
Encephalocele: anterior posterior view. Encephaloceles or meningoceles of the anterior skull base can be accessed by angling instruments superior and anterior in the nose. Endoscopes with 30- and 45-degree angled lenses are often helpful.
Encephalocele: axial view.
Encephalocele: sagittal view.
Initial nasal endoscopy. Zero degree endoscopic view of the left middle meatus reveals normal anatomic features of the lateral nasal wall, the uncinate process and the ethmoid bulla. These structures must be excised to provide surgical access to the encephalocele (dashed line, deep to visible structures), which originates from the roof of the ethmoid sinus.
Ethmoidectomy. After medialization of the middle turbinate, which is preserved, the uncinate process and the ethmoid bulla are excised. Careful removal of the anterior ethmoid sinus partitions will reveal the encephalocele.
Visualization of encephalocele and skull base defect. Careful dissection of ethmoid partitions is performed around the circumference of the encephalocele. The ethmoid skull base is skeletonized anterior and posterior to the encephalocele to visualize the margins of the bony skull base defect.
Reduction of encephalocele. The encephalocele is vaporized and reduced with pistol-grip-type bipolar forceps. The resection of the encephalocele is performed until the remnant encephalocele pedicle is reduced to the level of the adjacent skull base.
Repair of skull base dehiscence. (A) The skull base defect is prepared for closure by first circumferentially demucosalizing the defect, exposing the bony ethmoid roof and the entirety of the bony dehiscence. For dehiscences larger than 5 mm in diameter, a rigid layer of bone or cartilage (dashed line) is placed between the dura and bony skull base. Bone or cartilage may be harvested from the nasal septum; alternatively, a prosthetic absorbable plate may be utilized.
(B) A free mucosal graft harvested from the nasal floor is then placed to cover the entirety of the bony defect (inset, transverse view of layered repair). The repair is further supported by a layer of microfibrillar collagen and a methylcellulose expansile nasal sponge.
Petrous apex cholesterol granuloma, axial view. This lesion, which extends medial to the carotid artery, has a favorable anatomy for drainage into the sphenoid sinus. (5, trigeminal nerve; SS, sphenoid sinus with the intersinus septum removed.)
The cholesterol granuloma makes a bulge in the posterolateral wall of the sphenoid sinus just medial to the carotid artery.
The cyst is marsupialized into the sphenoid sinus.
Petrous apex cholesterol granuloma, axial view. This lesion, which extends to the medial edge of the carotid artery, is accessible for drainage into the sphenoid sinus.
Aspect of the posterolateral wall of the sphenoid sinus to be opened (dashed area, arrow) to create the pathway needed to gain access to the cyst.
Removal of bone with an angled drill.
Incision of the cyst wall and evacuation of its contents. To avoid possible stenosis of the drainage portal, the widest possible marsupialization should be created.
Petrous apex cholesterol granuloma, axial view. This lesion, which is situated well lateral to the medial edge of the carotid artery, is not easily accessible for drainage into the sphenoid sinus.

From ATLAS OF SKULL BASE SURGERY & NEUROTOLOGY. Thieme. ©2009

All images are copyright by RK Jackler. Permission granted for non-profit educational use of images, with attribution to their source.

Created by: Robert Jackler (surgeon) and Christine Gralapp (artist).

With contributions by:
Nikolas Blevins, Griffith Harsh, Michael Kaplan, Lawrence Pitts, Charles Yingling, and Corey Mass.

For legend references, please see the print book.