T1 pre-gad PDW T2

Diagnosis: Interhemispheric arachnoid cyst with probable Dandy-Walker malformation

Arachnoid cysts are most likely congenital meningeal malformations and make up 1% of nontraumatic intracranial masses. Most occur in childhood with boys outnumbering girls 3 to 1. Over 1/2 are in the middle cranial fossa. Other locations include the quadrigeminal & suprasellar cisterns, CP angle and the convexities. An interhemispheric location is unusual. Dysgenesis of the corpus callosum has been reported associated with an interhemispheric arachnoid cyst. 75% may be symptomatic, presenting with seizures, headache or focal neurologic deficit. They contain fluid which is similar , but not identical to CSF but does follow CSF on all pulse sequences. Hemorrhage into the cyst is a possible complication which may alter the signal characteristics. The cyst itself should have no internal components and there is no enhancement.

This is obviously not a very straight-forward case. This patient has a long history of what is reported to be supratentorial and posterior fossa arachnoid cysts which have been treated since childhood by multiple shunts and surgical procedures. On imaging; however, the posterior fossa cyst is more reminiscent of a Dandy-Walker complex since it communicates with a dilated fourth ventricle. In addition, this patient has a history of prior subdural hematomas which probably explains the cystic, loculated lesion in the left parasagittal occipital region. Other things which may mimic a supratentorial arachnoid cyst include porcephalic cyst, cystic neoplasm, epidermoid or open lip schizencephaly. Related Cases

Hirohata M, Matsuo H, Miyagi J, et al. Interhemispheric arachnoid cyst; report of three cases. No Shinkei Geka, Jun 1992; 20(6):p701-5.

Heier LA, Zimmerman RD, Armster JL, et al. Magnetic resonance imaging of arachnoid cysts. Clin Imaging, Dec 1989; 13(4):p281-91.















































Epidermoid Arachnoid cyst Dandy-Walker