FIGURE 27.1 A. Preoperative, T1-weighted postcontrast axial MRI showing the direct relationship of a tumor of Meckel’s cave (arrows) with the sphenoid (SS) and maxillary sinuses (MS). B. Intraoperative endoscopic endonasal view showing tumor within the left Meckel’s cave (MC) presenting directly to the surface of the sinus. (CR, clival recess; FR, foramen rotundum; ICA, internal carotid artery [paraclival/vertical petrous]; S, sella; VC, vidian canal.)

Perineural spread of sinonasal carcinoma to Meckel’s cave generally carries a poor prognosis, but, in the absence of radiographic or clinical evidence of cavernous sinus invasion, debulking, and/or removal of recurrent disease in this location, followed by focal irradiation for residual microscopic disease, can improve local control or palliation of neuropathic pain.

Rarely, tumors with a medial origin will extend to Meckel’s cave. Pituitary adenomas, nasopharyngeal angiofibromas, chordomas, and chondrosarcomas can all be followed into Meckel’s cave with relatively low risk, as they tend to displace the neural contents laterally without direct invasion of the nerve.

Rarely, inflammatory diseases (e.g., sarcoidosis), infections (e.g., tuberculosis), or metastatic disease (e.g., meningeal carcinomatosis) primarily involve the trigeminal nerve and/or Meckel’s cave. Their diagnosis can often be made by other means such as CSF analysis or inferred from other tests, but sometimes they do require biopsy. These biopsies can be performed endonasally with minimal morbidity or delay in subsequent treatment.

CONTRAINDICATIONS

The EEA is contraindicated for tumors that originate and are primarily growing in the posterior or lateral middle fossa with minimal extension into Meckel’s cave or the anteromedial middle fossa. Attempting to resect such tumors would require transection or extensive, unnecessary manipulation of the Gasserian ganglion.

Sinus infection is a relative contraindication for intradural endonasal surgery that requires treatment with antibiotics alone or in combination with drainage. Once the infection has resolved, intradural resection can proceed. Biopsy of the maxillary branch of the trigeminal nerve, peripheral to Meckel’s cave, is generally safe even in the setting of infection.

Neoplastic involvement of the petrous internal carotid artery (ICA) is a relative contraindication depending on the goals of surgery and the experience of the surgical team. If proximal control of the ICA is desired, an infratemporal skull base approach may be considered.

PREOPERATIVE PLANNING

Given the complexity and variability of pathologies, both magnetic resonance imaging (MRI) and computed tomography (CT) angiography are generally recommended for evaluation and operative planning. FIESTA or fine-cut T2 MRI sequences can help to determine the relationship of the proximal trigeminal nerve to the tumor. Coronal, postcontrast studies reveal the degree of involvement of the branches of the trigeminal nerve as they exit their neural foramina and can also reveal if there is tumor extension to the cavernous sinus. These factors should also be evaluated on fine-cut (SPGR) postcontrast axial images as they can significantly change the role, extent, or goals of surgery. It is often impossible to know the relationship of the trigeminal nerves and ganglion to the lesion, though this could prove critical for planning of the surgical approach. In the future, high-definition fiber tracking techniques may help to better define these types of relationships.

CT angiography is important to evaluate both bony involvement or erosion and vascular involvement and displacement, both of which are common with Meckel’s cave and middle fossa pathology. Enlargement of the foramen ovale and/or rotundum, erosion of the floor of the temporal fossa, tumor-related hyperostosis, and degree of pneumatization of the lateral recess of the sphenoid sinus all play a role in either surgical planning or differential diagnosis. Tumors such as schwannomas and meningiomas that enlarge Meckel’s cave over time can significantly displace the horizontal petrous, paraclival, and cavernous segments of the ICA. The position of the artery can affect accessibility as well as safety of resection and/or biopsy. Narrowing of the artery is a sign of significant involvement of its wall, and consideration should be given to balloon test occlusion, depending on the goals of surgery.

Both CT and MRI should be evaluated for signs of sinusitis so that it can be treated preemptively.

SURGICAL TECHNIQUE (VIDEOS 27.1 AND 27.2)

A team consisting of an otolaryngologist and a neurosurgeon working in tandem performs all surgeries. Endoscopic endonasal surgery (EES) lateral to the paraclival and cavernous ICA requires a team with significant experience working in the sellar and parasellar regions. ICA exposure and manipulation are likely to be necessary, and comfort with possible management strategies in the event of an injury is critical before attempting these intradural resections.

Patients are placed in three-pin Mayfield head fixation with their head in slight extension, rotated approximately 15 to 20 degrees to the right and with slight lateral flexion of the vertex to the left. Any head positioning should be tempered by concern for cervical spine immobility or stenosis. The patient is placed in reverse Trendelenburg position to decrease venous hypertension and blood loss. Decongestion of the nasal cavity is achieved by placement of oxymetazoline-soaked pledgets. Image guidance is registered, and then the midface and abdomen are prepped with Betadine and draped. Neurophysiologic monitoring includes monitoring of cerebral function with somatosensory evoked potentials (given the potential for ICA manipulation) and electromyography (EMG) of the motor branch (mandibular/V3) of the trigeminal nerve, third, fourth, and sixth nerves to help with their identification and preservation.

A binaural approach to Meckel’s cave is preferred since this improves visualization and access. The need for a vascularized flap for coverage of an exposed ICA or closure of a dural defect is anticipated. A contralateral septal mucosal flap pedicled on the posterior septal branch of the sphenopalatine artery is elevated and stored in the nasopharynx or maxillary sinus (ipsilateral to the flap) until needed. The posterior septum is detached from the sphenoid rostrum, and the bone of the rostrum is removed. Bilateral wide sphenoidotomies are performed. Resection of approximately 1 cm of the posterior septum improves the exposure.

A maxillary antrostomy is performed on the same side as the lesion. The sphenopalatine artery is sacrificed, and the sphenopalatine foramen is enlarged with a 1 mm Kerrison rongeur. The bone of the posterior wall of the maxillary sinus is removed to fully expose the contents of the pterygopalatine space. Within the sinus, the infraorbital nerve (branch of the maxillary nerve) is identified along the floor of the orbit as it courses medially toward the foramen rotundum.

The vidian nerve and its canal are a key anatomic landmark for this approach. The pterygopalatine contents should be carefully retracted laterally to identify the vidian nerve as it enters the bony canal within the pterygoid base (Fig. 27.2

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