Management of petrous endostosis in posterior fossa procedures for trigeminal neuralgia.

Objective: Within a series of 440 consecutive patients who underwent posterior fossa procedures for trigeminal neuralgia (TN), the site of neurovascular conflict was obscured by petrous endostosis in 15 patients. The surgical management and clinical outcomes of these patients are presented.

Methods: We retrospectively analyzed the prospectively collected data of all patients with a diagnosis of TN from 1980 to 2005. Clinical presentation, preoperative imaging, intraoperative findings, surgical technique, and outcomes were recorded. A postal follow-up questionnaire and a visual analog scale of 100 points were used for outcome assessment and patient satisfaction.

Results: All 15 patients presented with typical TN, had preoperative imaging suggestive of vascular compression of the trigeminal nerve root, and underwent standard retromastoid craniotomy. The juxta-petrous portion of the trigeminal nerve root was obscured by petrous endostosis. The neurovascular conflict was revealed and dealt with after drilling of the endostosis in 11 patients, and four patients had endoscopic-assisted exploration of the region of the endostosis. A pontotrigeminal vein caused compression in most cases. Three patients had endoscopic-assisted division of the vein. All patients had immediate relief of pain and were 100% satisfied with the results of surgery after a mean follow-up period of 38.6 months. Four patients developed a cerebrospinal fluid leak, and five patients experienced postoperative headaches.

Conclusion: Petrous endostosis is an uncommon finding in posterior fossa procedures for TN (3.4%). However, it can obscure the region of neurovascular conflict, which is venous compression in these cases. We have found that drilling away endostosis or using endoscopic-assisted microsurgery increases the chances of good outcome and avoids unnecessary rhizotomy. All magnetic resonance imaging scans should be inspected for evidence of petrous endostosis and, when present, a bone window computed tomographic scan should be performed to clarify the image and check for the presence of petrous air cells. If the endostosis is drilled, failure to detect and to seal these air cells thoroughly can result in postoperative cerebrospinal fluid rhinorrhea. Attention to these details will optimize the surgical results. However, the use of an angled endoscope avoids this problem and is now our preferred method.