Galassi classification of middle cranial fossa arachnoid cyst

The Galassi classification of middle cranial fossa arachnoid cysts​ is used to classify arachnoid cysts in the middle cranial fossa, which account for 50-60% of all arachnoid cysts.

Galassi et al published this classification in 1982, and remains the most widely used system for these lesions.

It is a simple system, using the size and degree of displacement of adjacent brain to divide cysts three types. The size also correlates with the ease with which the cyst communicates with the subarachnoid space as discerned on CT cisternography or phase contrast MRI.

Galassi type 1 middle cranial fossa arachnoid cyst

type II ​superior extent along sylvian fissure displacement of the temporal lobe slow communication with subarachnoid space

type III ​large, fills the whole middle cranial fossa displacement of not only the temporal lobe but also the frontal and parietal lobes often results in midline shift little communication with subarachnoid space

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