Anatomical Step-by-Step Endoscopic Endonasal Approach for Maxillary Nerve (V2) Rhizotomy and Case Series

Background: The endoscopic endonasal approach for selective maxillary nerve rhizotomy is a minimally invasive surgical option when indicated in refractory cases of V2 neuralgia. Although previous descriptions of endoscopic endonasal approaches to the pterygopalatine fossa for exposure of the maxillary branch of the trigeminal nerve have been published, a practical step-by-step guide to assist junior neurosurgical and skull base trainees at various levels in their training is lacking.

Methods: Six sides of three formalin-fixed, colored-injected specimens were dissected using 4-mm and 0- and 30-degree rigid endoscopic lenses and standard endoscopic equipment. The anatomical dissection was documented in stepwise 3D endoscopic images. A retrospective study of five representative case applications of patients with unilateral trigeminal neuralgia confined to the V2 branch who underwent an endoscopic endonasal approach for V2 rhizotomy were reviewed utilizing the Barrow Neurological Institute (BNI) composite pain score to compare outcomes.

Results: The endoscopic endonasal approach to the pterygopalatine fossa for exposure of the maxillary division of the trigeminal nerve for rhizotomy is an effective, reproducible method for the treatment of V2 neuralgia in selective refractory cases. Key steps include: maxillary antrostomy, posterior ethmoidectomy, transethmoidal sphenoidotomy, identification of the sphenopalatine foramen, exposure of the pterygopalatine fossa with removal of the posterior wall of the maxillary sinus, removal of the sphenoid process of the palatine bone, and identification of the palatovaginal neurovascular bundle. Transection and lateralization of the palatovaginal canal contents allows identification of the vidian nerve laterally. Elevation of the periosteum of the pterygoid base in a superior and lateral trajectory until identification of the foramen rotundum is performed. The periosteum of the pterygopalatine fossa is opened next to the foramen rotundum and V2 is isolated with a 360-degree dissection around the foramen rotundum. In some cases, removal of the posterior aspect of the orbital floor along the medial part of the inferior orbital fissure and removal of the medial orbital wall along the inferior aspect of the superior orbital fissure are important to facilitate exposure of the maxillary strut, which separates the foramen rotundum from the superior orbital fissure, and allow dissection around the nerve. All five patients who underwent endoscopic endonasal V2 rhizotomy had preoperative BNI composite pain scores of 5 of 5 indicating severe pain without relief despite prior medical and surgical treatments. Three of the patients had postoperative BNI scores of one-fifth indicating no pain. One patient had a postoperative BNI of two-fifths indicating some pain not requiring medication, and one patient had a postoperative BNI of three-fifths indicating some pain controlled by medication.

Conclusion: The endoscopic endonasal approach for maxillary nerve rhizotomy is an effective, minimally invasive treatment for selected patients with refractory V2 neuralgia. All five patients reviewed in our series experienced pain relief and expected numbness in V2 territory, with three of them experiencing complete relief of their pain. We describe a practical step-by-step approach to learning this technique, intended to be understood by trainees at various levels of knowledge and experience. Key surgical landmarks are also described.

 

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Artikel online veröffentlicht:
12. Februar 2021