Auditory Hallucinosis as a Presenting Feature of Interpeduncular Lipoma with Proximal P1 Segment Fenestration: Report of a Rare Case and Review of Literature on Peduncular Hallucinosis

The authors present a unique case of intracranial lipoma in the interpeduncular cistern, associated with proximal P1 segment fenestration. This patient is a 20-year-old male with extensive psychiatric history and complaints of recent auditory hallucinations. Cranial MRI (T1, T2 and FLAIR) showed a hyperintense lesion in the left aspect of interpeduncular cistern with a prominent flow void within the hyperintense lesion suggestive of a combined vascular-lipomatous lesion. CT angiography showed a high riding large tortuous P1 segment on the left side with proximal fenestration, the ectatic posteromedial limb harboring a fusiform dilated segment. Since there are anecdotal cases of cerebral aneurysms associated with intracranial lipomas, a conventional angiography was done, which confirmed a proximal left P1 fenestration and a fusiform dilated segment, and no aneurysm. There are few cases of hallucinations associated with avascular midbrain pathology reported in literature, but hallucinations associated with a combination of lipoma and arterial ectasia has never been reported. This article not only demonstrates the MRI and angiographic appearance of this rare lipomatous lesion, but also highlights this unique association and significance of auditory hallucinations as a clinical presentation, akin to peduncular hallucinosis.