Arachnoid cyst CT

On brain/spine CT scan, arachnoid cysts are characterized by cystic images with similar density to CSF and non-enhancing borders, mostly found in the middle cranial fossa while they only rarely occur in the spinal cord.

• Arachnoid cysts are cystic extra-axial lesions of the brain.
• On CT scans they are observed with a similar density to CSF, with sharp non-enhancing borders.
• The main differential diagnosis is the epidermoid cyst which present with irregular borders, while the arachnoid cyst is sharp but smooth. While the CT can is useful, an MRI is more precise on establishing its origin and location.

• Most cysts (50-60%) are found in the floor of the middle cranial fossa, while 1/4 to 1/3 of occur in the posterior fossa, particularly in the retrocerebellar, cerebellopontine, and quadrigeminal plate cisterns. Rarely, they may be found in the spinal cord.^[1][2]
• Arachnoid cysts tend to occur mostly on the left side.^[3]