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: 46 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 


MRI Brain

There is an extraaxial CSF density space measuring 41.4x61.1x79 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

Galassi type III arachnoid cyst are large and fill the whole middle cranial fossa displacing the temporal, frontal and parietal lobe, with extension along the sylvian fissure and communicate 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 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. 

PlayAdd to Share

Case information

rID: 40204
Published: 12th Oct 2015
Last edited: 14th Aug 2019
Inclusion in quiz mode: Included

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.