Galassi classification of middle cranial fossa arachnoid cysts
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. 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.
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 1.
- small, spindle-shaped
- limited to the anterior portion of the middle cranial fossa, below the spenoid ridge
- free communication of subarachnoid space
- superior extent along sylvian fissure
- displacement of the temporal lobe
- slow communication with subarachnoid space
- 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
- 1. Yildiz H, Erdogan C, Yalcin R et-al. evaluation of communication between intracranial arachnoid cysts and cisterns with phase-contrast cine MR imaging. AJNR Am J Neuroradiol. 2005;26 (1): 145-51. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 2. Galassi E, Tognetti F, Gaist G et-al. CT scan and metrizamide CT cisternography in arachnoid cysts of the middle cranial fossa: classification and pathophysiological aspects. Surg Neurol. 1982;17 (5): 363-9. Pubmed citation