Arachnoid cysts are benign cysts related to the arachnoid membranes in the brain and spinal canal.

These cysts do not communicate with the ventricular system.

 Fluid in the cysts is CSF and may be clear or xanthochromic.

 Most are developmental, but can be aquired with prior surgery, neoplasms,  hemorrhage or infection.     

The most common location is the middle cranial fossa(tip of temporal lobe 50%), but cysts can occur in the choroidal fissure, interhemispheric fissure, cisterna magna, quadrigeminal cistern(10%), suprasellar cistern(10%), vermian fissures or over the convexities, CP angle (11%) as well as in the spinal canal. 

    Patients are usually asymptomatic, but can present with headache or focal neurological symptoms.    

Findings include mass effect on the adjacent brain, lack of contrast enhancement and calvarial bulging.    

 Differential can include subdural fluid collections which have enhancing membranes and porencephalic cysts which have surrounding brain parenchyma, epidermoid cyst which has restricted diffusion on MRI. 

Rathke’s Cleft Cyst are congenital, non-neoplastic sellar and suprasellar cysts derived from remanants of Rathke’s pouch.

These cysts are found during routine autopsies in 13-22% of cases. 

Rathke’s Cleft Cyst can have intracystic nodule with high signal intensity on T1-weighted images and low signal intensity on T2-weighted images may be diagnostic indicator of Rathke’s cleft cyst.   

   Most patients do not require treatment. If treatment is need, fenestration, aspiration, unroofing of the cyst and removal can be considered. 

Take Home Message: 

Mnemonic for Sellar and Suprasellar Masses: SATCHMO

S-Sarcoidosis

A-Aneurysm, Arachnoid cyst

T-Teratoma

C-Craniopharyngioma, Chordoma

H-Hypothalamic glioma, Hemartoma

M-Meningioma, Mets, Mucocele

O-Optic nerve glioma, Neuroma