Epidermal inclusion cyst: cytomorphological features and differential diagnosis.

Aspirates from 162 epidermal inclusion cysts (EIC) from 157 patients were analyzed in order to elaborate on specific cytologic features. The most common site involved was the head and neck region (96 cases; 59.2%). The maximum patients were in the 3rd and 4th decades of life. Aspirates from EIC showed a clear background, with high cellularity, and nucleate and anucleate squames. Keratinous material was seen in some cases but the amount was less compared with the cellular elements. In 31 cases, a diagnosis of infected EIC was made on the basis of dense inflammatory infiltrate in addition to the squames. Histopathology was available in 56 cases out of which EIC was diagnosed in 45 cases. The remaining 11 cases were dermoid cyst (5 cases), branchial cyst (2 cases), pilomatricoma (2 cases), and sebaceous and thyroglossal cyst (1 case each). Thus, EIC should be differentiated from other squamous cell containing lesions. (c) 2008 Wiley-Liss, Inc.