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The Endoscopic Endonasal Approach for Craniopharyngiomas
Craniopharyngiomas are benign tumors originating from squamous epithelial remnants of Rathke pouch that can arise anywhere along the axis from the nasopharynx to the hypothalamus. , Their consistency can be cystic, solid, or a combination of both, and there is often intralesional calcifications occurring in 60% to 80% of cases. Craniopharyngiomas are relatively rare, accounting for only 1% to 5% of all intracranial tumors in the United States; however, this proportion varies widely based on age and geographic location with rates as high as 7.9% to 11.6% in Europe and Africa, respectively. , The estimated overall incidence is 1.3 to 1.4 cases per million persons per year, and there is a well-described bimodal age of presentation, occurring most commonly in children (5 to 14 years) and older adults (50 to 74 years). , These features combined with an unpredictable and poorly understood pathobiology have complicated efforts to establish standard management strategies. Consequently, the optimal surgical approach for craniopharyngiomas remains somewhat controversial.
The surgical resection of craniopharyngiomas has historically been performed using various microscopic transcranial approaches, such as the subfrontal, frontolateral, and pterional routes. Transsphenoidal approaches, whether microsurgical or endoscopic, have been restricted to intrasellar tumors or those with suprasellar subdiaphragmatic extension. , Nonetheless, over the past 20 years, technological advancements coupled with new surgical techniques have led to the development of minimally invasive surgical approaches that offer increased effectiveness with significantly decreased morbidity. This has resulted in increased effectiveness for both transcranial and transsphenoidal approaches. Nevertheless, the surgical management of craniopharyngioma continues to be a significant challenge, particularly when the goal is gross total resection (GTR), which can be difficult to achieve without significant morbidity. Despite the noninfiltrative “benign” histopathology, complete removal is not always possible due to the intimate association of the tumor with vital neurovascular structures where they can be unrelentingly adherent. Furthermore, craniopharyngiomas can recur even after radical resection, and the surgical removal of recurrent tumor is an even more complex challenge due to scarring and adhesions to critical structures. , ,
The introduction and refinement of the extended transsphenoidal approach, initially described by Weiss, have created a new paradigm in transsphenoidal surgery, opening a direct corridor to the suprasellar space. This extended route for resection of craniopharyngiomas was successfully adopted by Laws et al. and has now become a standard approach. , Although the endoscope was initially introduced to transsphenoidal surgery for the treatment of pituitary tumors, its panoramic view has increased the versatility of the transsphenoidal approach and permitted its expansion to different parts of the skull base, thus allowing the removal of supradiaphragmatic lesions. Furthermore, because craniopharyngiomas are often infrachiasmatic midline tumors, the endonasal route provides the advantage of direct access to the tumor without the need for brain or optic nerve retraction. ,
The endoscopic endonasal approach (EEA) to craniopharyngiomas provides a direct caudal to cranial surgical corridor. Given the tumors are most often infrachiasmatic, the original classification of craniopharyngiomas in relation to the optic chiasm (prefixed or postfixed) is impractical. With the EEA, the infundibulum becomes the structure of reference; therefore, craniopharyngiomas have been reclassified accordingly: type I, preinfundibular; type II, transinfundibular; type III, retroinfundibular is further subdivided on the basis of rostral or caudal extension, whether the lesion extends to the anterior third ventricular (IIIa: infundibular recess, hypothalamic or IIIb: interpeduncular cistern); and type IV, isolated third ventricular and/or optic recess (not accessible by EEA) ( Fig. 17.1 ). Not surprisingly, specific surgical variations are required for each subgroup. In the following sections, we will describe the surgical nuances on the basis of our experience with the EEA for the treatment of craniopharyngiomas. We aim to highlight the feasibility of this technique and evaluate its advantages and limitations as compared with the transcranial and transsphenoidal microscopic approaches.
Types of craniopharyngiomas.
Surgical Technique
Technical Nuances in Craniopharyngioma Surgery
The EEA involves the team of two surgeons, using a three-hand or four-hand technique that takes advantage of the visualization provided by rod lens endoscope (18 cm in length, 4 mm in diameter; Karl Storz Endoscopy-America, Inc., Culver City, CA) of varying lens angulations, primarily 0 degrees and 45 degrees. The surgical team is usually composed of an otolaryngologist and a neurosurgeon experienced in endoscopic endonasal surgery. The otolaryngologist performs the sinonasal approach and then drives the endoscope to provide a dynamic view of the surgical field, while the neurosurgeon performs a bimanual dissection of the intradural structures. As in any other surgery, the EEA for the removal of craniopharyngiomas comprises three portions: exposure, tumor resection, and reconstruction.
Exposure
Following the induction of general anesthesia, the patient’s head is placed in a three-point fixation system in a slightly extended position to optimize access to the anterior cranial base. The head is rotated 5 to 10 degrees toward the surgeons (the patient’s right), and the neck is tilted to the left. Baseline somatosensory-evoked potentials are established, and image guidance registration is performed using a mask protocol (Stryker Navigation, Leibinger Corp., Kalamazoo, MI) using the preoperative computed tomography angiogram fused to a high-resolution magnetic resonance imaging. During setup, the nose is decongested with topical 0.05% oxymetazoline applied with 0.5 × 3-inch cottonoids. The midface and the periumbilical area are prepped and draped, and a fourth-generation cephalosporin antibiotic is administered for perioperative prophylaxis. The thigh can also be prepped for possible fascia lata graft. Preoperative testing of intranasal flora is performed, and vancomycin is also given if methicillin-resistant Staphylococcus aureus colonization is present. Preoperative steroids are not routinely administered, unless the patient has baseline adrenal insufficiency secondary to tumor infiltration.
We customarily begin the procedure with removal of the inferior half of the right middle turbinate. Thereafter, the most posterior aspect of the posterior ethmoid sinuses is removed to expose the lamina papyracea bilaterally. A pedicled nasoseptal flap (Hadad–Bassagasteguy) is raised from the widest nasal cavity, commonly the right given the middle turbinectomy, using a standard technique (see Reconstruction for details). At this point, the posterior 2 cm of the nasal septum is removed, and the left middle turbinate is lateralized but not resected. A wide sphenoidotomy is opened, enlarging the natural ostium until the lamina papyracea is in plane with the lateral wall of the orbit, the roof of the sphenoid sinus is in plane with that of the nose, and the bottom of the sinus is in full view. All intrasinus septae are carefully removed keeping in mind that they almost invariably end at the paraclival carotid artery. If the sinus is not well pneumatized, the bone is drilled until all surgical landmarks are well exposed. These include the optic nerves and intracranial carotid artery (ICA) canals as well as medial opticocarotid recess (MOCR) and lateral opticocarotid recess (LOCR) and the clival recess. The LOCR lies at the junction of the optic nerve and ICA canals corresponding to the optic strut, and the MOCR lies at the confluence of the optic canal and the paraclinoid carotid canal at the lateral portion of the tuberculum sellae. Image guidance is used to confirm the locations of these key anatomical landmarks. It should be remembered that continuous irrigation must be used to avoid thermal injury to the underlying optic nerve while drilling. To this end, we use a self-irrigating curved endonasal drill that has a completely protected shaft (Medtronic, Inc., Dublin, Ireland). Brisk venous bleeding may be encountered during drilling of the sella, most commonly from the superior intercavernous sinus (SIS) or the point of insertion of the SIS into the cavernous sinus. This bleeding can be controlled with injectable collagen-based hemostatic agents (Floseal Baxter, Inc., Deerfield, IL) mixed with thrombin or alternatively by packing with microfibrillar collagen (Avitene, Ethicon, Inc. Summerville, NJ).
The EEA opens an unobstructed corridor connecting the nasal cavities and the sphenoid sinus, thus, creating a single, large working cavity allowing bimanual access. It is important to note that the anterior boundary of the exposure is the posterior ethmoidal arteries (PEAs), which are encountered 4 to 7 mm anterior to the optic nerve and just anterior to the rostrum of the sphenoid. Staying posterior to the PEAs prevents injury to the cribriform plate and the olfactory system associated with it. The caudal limit of the approach is the clival recess. Thus, the rostrocaudal axis of the EEA for craniopharyngioma extends from the PEAs rostrally to the clival recess caudally. The endoscope is kept in the patient’s right nostril, slightly elevating it superiorly to the 12-o’clock position, to create space for the suction and dissection instruments that are introduced at the 6-o’clock position. The bone over the sellar face is removed, and the planum sphenoidale is removed anteriorly up to the anterior margin of the tumor, as determined by image guidance. A complete removal of the tuberculum sellae, including the MOCRs bilaterally, is mandatory to expose the opticocarotid cisterns to allow adequate suprasellar exposure for safe and efficient tumor resection. With the bony removal completed, the dura is opened similarly to a book, first with a midline incision, followed by an orthogonal incision above and below. An important technical nuance of the EEA for suprasellar lesions pertains to the management of the SIS. In craniopharyngioma surgery, there is commonly both intrasellar and suprasellar disease, thus requiring the exposure of both compartments. The SIS must therefore be divided, whereas it is not necessary when resecting a purely surpasellar lesion (tuberculum sellae meningioma). Incisions above and below the SIS are placed to allow the insertion of a bipolar electrocautery (Endopen, Sutter Inc., Freiburg, Germany) with one blade on each side of the sinus to facilitate its coagulation. The incision is extended across the SIS posteriorly toward the pituitary stalk, allowing complete exposure.
As opposed to EEA for the resection of meningiomas, craniopharyngiomas have specific anatomical hallmarks due to the origin of the tumor. It is critical for the surgeon to understand these relationships to avoid intraoperative complications. Because the tumor has its origin on the pituitary stalk, the suprasellar arachnoid membrane with the superior hypophyseal arteries (SHAs) is displaced anteriorly against the dura of the tuberculum. Thus, care must be taken during dural opening to avoid injury to the SHAs. A wide exposure combined with the magnified, high-definition view provided by the endoscope facilitates the identification and preservation of the SHAs and other subchiasmatic perforating vessels that are displaced over the lateral dome of the tumor preventing inadvertent devascularization of the optic apparatus and infundibulum.
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