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

Abstract

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 magnetic resonance imaging (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. Computed tomography (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 a vascular midbrain pathology reported in literature, but hallucinations associated with a combination of lipoma and arterial ectasia have 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.

Keywords: Auditory hallucinosis; interpeduncular lipoma; peduncular hallucinosis; posterior cerebral artery fenestration; vascular ectasia.

Figure 1.. Noncontrast axial head CT showing hypodense lesion in the left ventral perimesencephalic region with no adjacent edema or significant mass effect.

Figure 2.. a, b, c, d, e: Axial MRI brain (T2, FLAIR, T1, T1 with contrast, GRE, respectively) and f, g, h: MRI brain (FLAIR midsagittal, T2 coronal and T1 coronal with contrast, respectively) showing extra-axial single hyperintense lesion in the left aspect of interpeduncular space with area of hypointensity within the hyperintense lesion without any contrast enhancement suggestive of lipoma with ectatic left P1 segment with possible fenestration.

Figure 3.. CT angiography showing axial (a), sagittal (b) and coronal (c) views, along with a reconstructed view (d) of ectatic left P1 segment with fenestration, as well as no aneurysm.

Figure 4:. a, b, c and d. Conventional cerebral angiogram confirmed a high riding large tortuous P1 segment on the left side with a proximal fenestration better seen in (d) where the ectatic posteromedial limb has a fusiform dilatation; no evidence of a distinct aneurysm was seen.