Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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April 23, 2020
Mesencephalic Exophytic Cavernous Malformation
- Background:
- Cavernous malformations are occult lesions on catheter angiograms (formerly known as cryptogenic vascular lesions). The estimated incidence is approximately 0.5% (0.4–0.6%). The prevalence in the brain stem varies from 8.5% to 35%. They may be single or multiple, familial or sporadic (80%), and congenital or de novo.
- The most common location in the brain stem is the pons (62%), followed by the midbrain (14%), pontomesencephalic and pontomedullary junction (12%), and medulla (5%).
- Clinical Presentation:
- It varies from headaches to neurologic deficits depending on the extent of hemorrhage and destruction of brain parenchyma.
- Key Diagnostic Features:
- Typically have lobulated appearance with signal dephasing on T2* sequences and commonly internal septa
- Atypical lesions can be exophytic or even within the cistern (only few reports, with no actual percent available in the literature).
- A complete T2-hypointense rim may be absent and no associated siderosis in the adjacent parenchyma seen.
- Atypical locations are usually in small case series or case reports, so the real prevalence and incidence are hard to establish.
- Differential Diagnoses:
- Epidermoid cyst: It follows CSF signals and shows diffusion restriction.
- White epidermoid cyst: Has high protein content and shows high signal intensity on T1-weighted images and low signal intensity on T2-weighted images
- Meningioma: Shows intense enhancement
- Melanotic schwannoma: Shows some cystic component and enhancing components
- Treatment:
- Surgical resection is often risky with brain stem lesions, though proper surgical corridors are well established.
- Radiosurgery may be an option, with various degrees of success in the published series.
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