Endodermal Cyst Arising from the Oculomotor Nerve: A Case Report Outlining the Novel Insertion of Cysto-subarachnoid Shunt for Refractory Disease

Background Endodermal cysts of the oculomotor nerve are rare presentations. Only case reports are available to help guide clinicians with managing this rare entity. Case Description A 3-year-old boy presented with an acute on chronic left oculomotor nerve palsy due to a left interpeduncular cistern cyst found on magnetic resonance imaging. He underwent a left pterional craniotomy and fenestration of the histologically proven endodermal cyst and had initial improvement at the 2-month review. He subsequently developed clinical and radiologic evidence of recurrence and was treated surgically with a refenestration and insertion of a cysto-subarachnoid shunt through a trans-sylvian approach. At 6-month follow-up, there was complete resolution of the oculomotor nerve palsy with interval development of oculomotor synkinesis. Conclusions Magnetic resonance imaging is an essential modality in the follow-up of these patients postoperatively in the setting of unchanged or deteriorated neurology. Fenestration of the cyst is appropriate first-line surgical management; however, a cysto-subarachnoid shunt is a safe consideration in recurrent, symptomatic cysts and provides sustained symptom resolution.