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Findings: Axial T1 and T2 precontrast and post contrast axial and sagittal T1 images are shown. The precontrast images show a mass within the pons which is heterogeneously hyperintense on T1. At the posterior aspect a hyperintense "popcorn-like" structure is present. The T2 image shows areas of hypointensity within the mass mixed with hyperintensity. The post contrast images do not show significant enhancement.
Diagnosis: Cavernous hemangioma.
Discussion: The mass has mixed signal characteristics consistent with hemorrhage in different stages of evolution. A cerebral angiogram was performed which is not shown and was normal. Differential possibilities include a cavernous angioma versus a hemorrhagic tumor, which would be likely of glial origin. Differentiation between benign versus tumoral hemorrhage is not clear-cut. However, persistent edema over time, disorderly evolution of hemorrhage, and a complex heterogeneity of signal characteristics favor tumor. Characteristics of benign hemorrhage would include formation of a complete hemosideran ring and resolution over time of edema and mass effect.
This lesion is a cavernous angioma which is a vascular malformation consisting of endothelial lined sinusoidal spaces without brain mixed in. The risk of hemorrhage per year is approximately .5%. This is significantly lower than the risk of an arterio-venous malformation which has an approximate risk of 4% hemorrhage per year. In approximately 50% of cases of detected cavernous angiomas, multiple lesions are present. Approximately 80% are supratentorial, most commonly found in the frontal or temporal lobes, basal ganglia, or deep white matter. Approximately 20% are infratentorial and are most likely located in the pons or cerebellar hemispheres. They are classically described as "popcorn-like" lesions that have mixed signal intensity due to hemorrhage in different stages of evolution. No angiographic finding is usually shown. Occasionally, however, a faint blush may be present angiographically. Patients usually present with an acute neurologic deficit or seizure.
References:
Osborne A. Diagnostic Neuroradiology. Mosby, 1994.
Osborne A. Introduction to Cerebral Angiography. Lippincott-Raven, 1997.
Dahnert W. Radiology Review Manual, 3rd Edition, 1993:196-197.
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