Arachnoid cyst - Galassi type III

Case contributed by Dr Subash Thapa


Vague headache and loss of consciousness one episode 3 month back.

Patient Data

Age: 45 years
Gender: Female

ASNR 2016: This case was submitted as part of the American Society of Neuroradiology (ASNR 2016) Case Of The Day competition, in collaboration with 

There is a large left extra-axial cyst, measuring 41 x 61 x 79 mm in the left middle cranial fossa extending into the left Sylvian fissure displacing frontal and parietal lobe. It shows CSF signal in all the sequences with facilitated diffusion on DWI. There is displacement of the vessels with remodeling and thinning of the adjacent bone. There is no solid component or wall calcification.

Case Discussion

MRI features are of a large Galassi type III arachnoid cyst that fills the whole middle cranial fossa displacing the temporal, frontal and parietal lobe, with extension along the Sylvian fissure and communicates with subarachnoid space. It is important to note that the Galassi classification is not commonly used and it has a dubious clinical utility. 

Epidermoid cysts can sometimes mimic as arachnoid cysts, but they usually are partially or entirely not suppressed on FLAIR and show restricted diffusion on DWI. Epidermoid cysts also show a scalloped border that tends to insinuate into compartments and encase the vascular and neural structures.

It is hard to link the patient clinical symptoms directly to the presence of the arachnoid cyst.

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