Abscedation of posterior fossa dermoid cysts.

Dermoid cysts of the posterior fossa are uncommon. When associated with a dermal sinus, these cysts are often diagnosed during early childhood. 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-month-old girl who had a congenital dermal sinus leading to an intradural dermoid cyst. In addition to the midline dermoid cyst, computerized tomography revealed an enhancing lesion extending into the adjacent left cerebellar hemisphere. Suboccipital craniectomy was undertaken after 2 days of external ventricular drainage, and the infected dermoid and adjacent cerebellar abscess were excised. Cultures of the operative specimen revealed Corynobacterium aquaticum, Enterobacter sakazakii and Enterobacter cloacae, requiring 6 weeks of intravenous antibiotic therapy consisting of ceftriaxone, penicillin and gentamicin. A diligent literature search revealed only 24 sporadic cases reported over a period 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 these patients underwent posterior fossa surgery, with mortality and morbidity rates of 13% and 10%, respectively. Eleven (40%) children had suppuration within the cerebellar parenchyma, while the rest had abscedation of the dermoid cyst alone. Among the cases reviewed S. aureus was the most common agent, occurring with a probability of 64%. Key issues for appropriate management of these benign lesions are discussed.