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Findings: Image #1 is an axial T1 weighted image through the brain demonstrating a large region of decreased signal within the left cerebral hemisphere with an associated septation. There is an associated mass affect with minimal subfalcine herniation and effacement of the left lateral ventricle.
Image #2 is a T2 weighted axial image at the same level demonstrating diffusely increased signal. There is again demonstration of the internal septation. The imaging characteristics follow CSF on both sequences.
Diagnosis: Neuroepithelial cyst
Discussion: Neuroepithelial cysts represent a heterogenous group of lesions of uncertain etiology. They most likely arise from sequestration of developing neural ectoderm and are lined by epithelial like cells. Although neuroepithelial cysts can be identified at any age, they predominate in the older population. These cysts may occur anywhere within the intra-axial central nervous system, but are most commonly found in the choroid plexus, choroid fissure, cerebral ventricles, and occasionally within the intracranial parenchyma. Of these, the choroid plexus is the most common site. While most choroid plexus cysts are asymptomatic, large ventricular ependymal cysts may cause obstructive hydrocephalus. In addition, intraparenchymal cysts may be associated with headache and seizures.
On computed tomography, the cystic structure will demonstrate homogeneously low density consistent with CSF attenuation. There will characteristically be lack of enhancement or calcification. MRI will demonstrate the signal characteristics of the cystic structure to follow CSF on all imaging sequences. In addition, there should be no enhancement following Gadolinium administration. The differential diagnosis is somewhat limited, but would include a predominantly cystic astrocytoma.
References:
Osborn A. Diagnostic Neuroradiology. Mosby, St. Louis; 1994:646-648.
Sherman JL. MR Imaging of CSF Like Choroidal Fissure and Parenchymal
Cysts of the Brain. AJNR. 1990;11:939-945.
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