[Epidermoid cysts of the cerebellopontile angle. 6 cases].

6 cases of cerebello-pontine angle (CPA) epidermoid cysts were encountered from 1970 up to 1983. This series accounts for 3,3% of 177 CPA tumours operated on during the same period. Epidermoid cysts result from heterotopia of ectoblastic tissue and CPA is their most frequent site of development. The wall of the cyst is composed of a stratified squamous epithelium. The inside of the cyst is filled with soft waxy material resulting from the desquamation of keratin of the cyst wall. Macroscopically, the cyst is extensive and usually closely attached to the brain stem, cranial nerves and vessels. The commonest clinical picture is that of a trigeminal neuralgia usually typical of tic douloureux. Plain x-ray films of the skull disclose no abnormalities. Air encephalography was performed in an early case: it showed an obliteration of the cerebello pontine cistern by the cyst mass, with no air injection of the tumor as mentioned elsewhere. Computerized tomography made other procedures obsolete in our 4 latest cases: it showed a non-enhancing low-density mass filling the CPA. Hypodensity characteristics can make differentiation from dermoïd and arachnoid cysts. In a patient, auditory evoked response were lengthened bilaterally and suggested a brain stem compression rather than a cochlear nerve involvement. Operative treatment was performed in all of our 6 patients through a suboccipital craniotomy with the aid of the operative microscope. The aim of surgery should be, whenever possible, total removal of the capsule. A partial section of the fifth nerve is not needed. No patient died postoperatively.(ABSTRACT TRUNCATED AT 250 WORDS)