ABSCEDATION OF POSTERIOR-FOSSA DERMOID CYSTS

Dermoid cysts of the posterior fossa are uncommon. When associated wit h a dermal sinus, these cysts are often diagnosed during early childho od. The main risk of such an association is contamination of the cyst leading to abscedation of the dermoid itself or formation of daughter abscesses within the cerebellar hemisphere. We recently treated a 20-m onth-old girl who had a congenital dermal sinus leading to an intradur al dermoid cyst. In addition to the midline dermoid cyst, computerized tomography revealed an enhancing lesion extending into the adjacent l eft cerebellar hemisphere, Suboccipital craniectomy was undertaken aft er 2 days of external ventricular drainage, and the infected dermoid a nd adjacent cerebellar abscess were excised. Cultures of the operative specimen revealed Corynobacterium aquaticum, Enterobacter sakazakii a nd Enterobacter cloacae, requiring 6 weeks of intravenous antibiotic t herapy consisting of ceftriaxone, penicillin and gentamicin. A diligen t literature search revealed only 24 sporadic cases reported over a pe riod of 56 years. All 24 cases were in children (mean age 17 months), and one-third were in infants under the age of 1 year. All but 1 of th ese patients underwent posterior fossa surgery, with mortality and mor bidity rates of 13% and 10%, respectively. Eleven (40%) children had s uppuration within the cerebellar parenchyma, while the rest had absced ation of the dermoid cyst alone. Among the cases reviewed S. aureus wa s the most common agent, occurring with a probability of 64%. Key issu es for appropriate management of these benign lesions are discussed.