Findings
Axial T2 image(1) shows T2 hyperintense extra-axial lesion involving the right cerebellomedullary cistern. It shows hypointense signal intensity in the axial FLAIR(2) and T1(3) sequences suggestive of clear fluid containing lesion. No diffusion restriction is seen in the DWI image(4) and the lesion shows no blooming in the SWI images(5). In the 3D CISS sequence(6), the lesion shows fluid signal and causes displacement of the adjacent vessels and cranial nerves.
Diagnosis
Arachnoid cyst.
Summary
Fluid signal extra-axial intracranial lesions have two important differentials – arachnoid cyst and epidermoid cyst. DWI is a crucial sequence in differentiating these two entities with the former reflecting no diffusion restriction while the latter demonstrating diffusion restriction.
Further reads
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