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 1.
Usage
Galassi et al. published this classification in 1982, and at the time of writing (June 2016), it remains the most widely used system for these lesions.
Classification
It is a simple system, using the size and degree of displacement of the adjacent brain to divide cysts into 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 1.
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type I
small, spindle-shaped
limited to the anterior portion of the middle cranial fossa, below the sphenoid ridge
free communication of subarachnoid space
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type II
superior extent along the Sylvian fissure
displacement of the temporal lobe
slow communication with subarachnoid space
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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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