Extraosseous endolymphatic sac low-grade adenocarcinoma mimicking posterior fossa meningioma

Low-grade adenocarcinoma arising from the endolymphatic sac is an uncommon tumor that is characterized clinically by hearing loss and radiologically by temporal bone destruction. The authors report a case of low-grade adenocarcinoma of endolymphatic sac origin that mimicked a posterior fossa meningioma in both clinical and neuroimaging examinations. In this case, the most unusual and interesting feature was the lack of auditory symptoms and temporal bone destruction. The lesion occurred in a 21-year-old man who presented with headaches that had been increasing in frequency for 6 months and was associated with blurring of vision, diplopia, occasional nausea and vomiting, and gait disturbance. On examination, this patient exhibited bilateral papilledema, left sixth cranial nerve palsy, and gait ataxia. Neuroimaging studies revealed a large right posterior fossa tumor. At surgery, a hemorrhagic papillary adenocarcinoma of endolymphatic sac origin was found.