Isolated anisocoria from an endodermal cyst of the third cranial nerve mimicking an Adie's tonic pupil.

We present only the second reported case in the literature of a neuroenteric cyst involving the third cranial nerve. Our case is highlighted by the initial presentation of an isolated anisocoria, initially believed to represent an Adie's tonic pupil as interpreted by pharmacologic testing. False-positive results may occur with the dilute pilocarpine test.