Quadrigeminal Cyst
The quadrigeminal plate cistern is the fluid-filled space located cephalad to the fourth ventricle. The plate is comprised of the superior and inferior colliculi, while the cistern is the space immediately posterior to them. It is bounded by the quadrigeminal plate, the splenium of the corpus callosum, the cerebellar vermis, and the tentorial margin. Compression of this space may result in increased intracranial pressure and hydrocephalus by aqueductal stenosis.
The differential diagnosis for quadrigeminal plate cysts includes but is not limited to: Arachnoid cyst- a congenital anomaly of the arachnoid membrane that leads to CSF sequestration or focal impairment of CSF circulation. They are situated entirely within diverticular outpouchings of the subaracnoid space, in the arachnoid membrane. On MR using FLAIR and Diffusion Weighted Imaging, arachnoid cysts are isointense to CSF. Location and size vary considerably. CT will show hypodense structure distorting nearby structure with the same density as CSF. Rupture of an arachnoid cyst may cause a subdural hygroma or intercranial hemorrhage.
Epidermoid cyst- a true cyst lined by squamous epithelium. On MR using FLAIR the cyst may appear identical to an arachoid cyst, however it will differ on DWI. There is decreased with epidermoids so they will appear brighter than CSF, compared with an arachnoid cyst which follows the signal of CSF since there is no restricted diffusion..
Dermoid inclusion cyst- a rare ectodermal inclusion cyst with cheesy or greasy contents. Similar to epidermoid cysts, they are lined by squamous epithelium, but dermoid cysts have a more developed underlying stroma and may house dermal appendages (hair follicles & adnexae). On CT it will appear as a well circumscribed, rounded mass whose contents have negative attenuation values and may demonstrate hair. MRI will show signal hyperintensity on T1 and variability on T2.
Teratoma (well-differentiated)- A tumor of tissues inconsistent to the site of origin with derivatives from all three germ layers. May have both solid and cystic components and contain calcifications. CT and MR imaging is variable.
Treatment is surgical excision or fenestration of the cyst. A less invasive option is fenestration by endoscopic ventriculocystocisternostomy which has favorable preliminary results though long-term results are unknown.
