Epidermoid cysts of the posterior cranial fossa

Makhmudov U.B., Murusidze N.A.

(Burdenko Research Neurosurgical Institute of the Russian Academy of Medical Science, Moscow, Russia)

Epidermoid cysts of the posterior cranial fossa are rare neoplasms. According to the data of our Institute, they account for 0.5% of all CNS tumors. A morphologic substrate of epodermoid cysts is formed during the third week of an intrauterine period of development due to impaired embryogenesis and shifting of epithelial tissue into a neural tube.

Epidermoid cysts are found in liquor paths of the brain, subarachnoid cisterns or a ventricular system in the majority of cases. Spread of an epidermoid cyst within the limits of one basal cistern is a rare phenomenon. Usually they grow through arachnoid membranes and trabeculae, involve neighboring cisterns and occupy a space, where several cisterns are localized. Besides, they can affect dura mater, destruct bone structures and grow extracranially.

The pons lateral cistern is a place of primary localization of an epidermoid cyst rather often. Its subsequent growth takes place in the direction of the clivus, craniospinal transition or supratentorially. When an epidermoid cyst grows in the direction of the tentorial foramen, it spreads into the interpeduncular cistern or cisterna ambiens. Growth in the direction of the craniospinal transition results in spread of this cyst into a cavity of the forth ventricle through the foramen of Luschka. A primary epidermoid cyst of the forth ventricle can spread into the cerebellopontine cistern.

There were 78 patients with epidermoid cysts of the posterior cranial fossa, who were operated in the Burdenko Research Neurosurgical Institute in 1985-2000. A clinical syndrome, CT and MRI images of these cysts were studied.

A method of radical removal of epidermoid cysts of the posterior cranial fossa, stages and tactics of surgical treatment were worked out. Total removal was performed in 81.25% of patients. As for the rest cases, a part of a capsule was not removed because of its close interrelations with adjacent neurovascular structures.

Quality of surgical treatment was estimated on the basis of dynamics of a neurologic status, CT and MRI data before and after the operation. Modern rentgenologic methods and microsurgical technique ensure radical removal of epidermoid cysts with a good postoperative result.