Arachnoid cyst - middle cranial fossa

Case contributed by Ammar Haouimi

Presentation

Incidental finding.

Patient Data

Age: 2 years
Gender: Male

Large cystic lesion of extra-axial location in the left middle cranial fossa, extending to the insular region.  It displays an isosignal to the CSF signal on T1 and T2 sequences with no restricted diffusion. It compresses the temporal and frontal lobes with thinning of the adjacent inner table of the skull. No significant mass effect on the midline structures.

Peritrigonal areas of high signal on T2 sequences suggestive of terminal zones of myelination.

Case Discussion

MRI features of a large arachnoid cyst of the middle cranial fossa extending to the insular region, type III according to Galassi classification.

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