Differential Cranial Nerve Susceptibility to Compression by a Giant Cerebellopontine Angle Epidermoid Cyst: A Case Report and Literature Review.

Giant cerebellopontine angle (CPA) epidermoid cysts may envelop multiple cranial nerves, yet patients often present with clinically isolated trigeminal neuralgia. The anatomical basis for this selective vulnerability is incompletely appreciated in routine clinical practice. A 48-year-old man presented with a five-year history of progressive left-sided trigeminal neuralgia involving the maxillary and mandibular divisions. Pain had become severe and refractory to high-dose carbamazepine, with substantial functional and psychological decline. Neurological examination was otherwise unremarkable, with intact facial nerve function and normal hearing on preoperative audiometry. Brain magnetic resonance imaging revealed a 6.1 cm left CPA epidermoid cyst circumferentially involving the trigeminal, facial, and vestibulocochlear nerves, without extension into the internal auditory canal. Despite this extensive radiological involvement, clinical dysfunction was confined to the trigeminal nerve. The patient underwent retrosigmoid craniectomy with maximal safe resection, prioritizing decompression of the trigeminal root entry zone while leaving capsular remnants adherent to cranial nerves VII and VIII to preserve neural function. Trigeminal pain resolved completely and immediately after surgery, allowing discontinuation of all analgesic medication. A mild high-frequency sensorineural hearing loss was the only postoperative deficit, with preservation of functional hearing. The selective trigeminal vulnerability observed in this case reflects the proximal location of the trigeminal central-peripheral myelin transition zone, which overlaps the root entry zone and is therefore exposed earliest to compressive forces from expanding CPA lesions. This case supports individualized surgical strategies that prioritize symptomatic decompression over radical resection in giant CPA epidermoid cysts.