A vascular malformation mimicking an intracanalicular acoustic neurilemoma. Case report. A patient with an enhancing, completely intracanalicular mass on magnetic resonance imaging was operated on for a presumed acoustic neurilemoma, but was found at surgery to have an intracanalicular vascular malformation. This rare lesion should be distinguished from angiomatous change within an acoustic neurilemoma and in the past has been termed "vascular tumor," "hemangioma," or "fibro-angioma." The clinical distinctions between intracanalicular acoustic neurilemomas and intracanalicular vascular malformations and the ability of magnetic resonance imaging to distinguish between the two are discussed. 