Resection of a Posterior Fossa Endodermal Cyst With Exoscopic Assistance: 2-Dimensional Operative Video.

Neurenteric cysts are rare benign congenital tumors of endodermal origin that most commonly occur in the cervical and upper thoracic spine, with only about 10% to 18% of the reported cases occurring intracranially.1 A definitive preoperative diagnosis is complicated by the variable appearance of neurenteric cysts on magnetic resonance (MR) imaging.2 The recommended treatment of neurenteric cysts is complete surgical resection when possible.3,4 We present a case of a posterior fossa neurenteric cyst. A 33-yr-old man without medical history presented with left-sided headache and mild left-sided facial numbness and weakness. Admission MR imaging revealed a nonenhancing mass, which was hyperintense on T1-weighted MR images, compressing the brainstem anteriorly. The lesion was isointense on T2 FLAIR images and hypointense on diffusion-weighted imaging, initially read as possible epidermoid cyst. The patient underwent a left-sided retrosigmoid craniotomy via far lateral transcondylar approach. The tumor was adjacent to both vertebral arteries, the left PICA, and cranial nerves (CN) VII-XII with superior extension to CN V. The cyst was encased in a thin capsule, and its contents were yellowish in color and ranged from thick liquid to colloidal and caseous consistency. The cyst also contained heavily calcified portions, which were excised using sharp dissection. Images of the cyst wall show that it is focally lined with ciliated columnar epithelium with intracellular mucin confirming an endodermal or neurenteric cyst. After the operation, the patient's symptoms resolved, and he was discharged on postoperative day 4. Postoperative MR images confirmed gross total resection. The patient consented to video production.