Orthokeratinized Odontogenic Cyst with an Associated Keratocystic Odontogenic Tumor Component and Ghost Cell Keratinization and Calcifications in a Patient with Gardner Syndrome.

Gardner syndrome (GS) is caused by mutations in the APC and besides adenomatous colorectal polyps includes such manifestations as osteomas, epidermoid cysts (ECs) and occasionally multiple pilomatricomas. More than 50 % of ECs in patients with GS exhibit pilomatricoma-like ghost cell keratinization. The latter may be explained by the fact that the development of both GS and pilomatricoma is driven by activation of the Wnt/β-catenin signaling pathway. A 62-year-old, Caucasian male with history of GS presented with a unilocular, mixed radiopaque/radiolucent mandibular lesion causing divergence and external root resorption of involved teeth. Histopathologically, the lesion was composed of two cystic components, an orthokeratinized odontogenic cyst (OOC) and a smaller one with characteristics of keratocystic odontogenic tumor (KCOT) featuring, focally, ghost cells and an epithelial morule-like structure. Dystrophic calcifications essentially similar to those seen in pilomatricomas were observed in the fibrous connective tissue wall. The KCOT and OOC epithelia revealed strong and diffuse cytokeratin (AE1/AE3) and β-catenin immunoreactivity. CD10 positive immunostaining was seen in the keratin and superficial spinous cell layers in both OOC and KCOT. The intraepithelial and mural ghost cells showed a cytokeratin (+), β-catenin and CD10 (-) immunophenotype. The diagnosis of OOC with ghost cell calcifications in association with KCOT was rendered. The patient was lost to follow-up. Although a coincidental co-existence cannot be excluded, ghost cell calcifications mimicking pilomatricoma-like changes in an unusual odontogenic cyst combining OOC and KCOT features as seen in this patient with GS may be explained by the common molecular mechanisms underlying the pathogenesis of cutaneous pilomatricomas and GS.