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Meningioma of the posterior cranial fossa with obstructive hydrocephalus

Case contributed by Ammar Haouimi
Diagnosis almost certain

Presentation

Signs of raised intracranial pressure.

Patient Data

Age: 75 years
Gender: Male

Large ovoid well-defined extra-axial mass of the posterior cranial fossa measuring 50 x 45 x 35 mm with a broad-based attachment to the posterior margin of the tentorium cerebelli. It shows an isosignal to the cortical grey matter on T1 and T2, slight high signal on FLAIR with a vivid homogeneous enhancement on post-contrast sequences. A thin peripheral rim of high signal on T2 "CSF cleft sign" indicating its extra-axial location. The adjacent sigmoid and lateral sinuses are compressed but patent. Perilesional vasogenic edema with a mass effect on the right cerebellar parenchyma, brainstem, and 4th ventricle which is compressed and displaced to the left with a tonsillar herniation.

Dilatation of the 3rd and lateral ventricles with transependymal edema in keeping with obstructive hydrocephalus.

Chronic small vessel ischemic changes are noted.

Case Discussion

MRI features most consistent with a large meningioma of the posterior cranial fossa compressing the 4th ventricle with tonsillar herniation and obstructive hydrocephalus.

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