Desmoplastic trichilemmoma (DT) is a variant of trichilemmoma, characterized by a central prominent desmoplastic component which may simulate invasive carcinoma. We have studied the morphologic and immunohistochemical features of seven cases of DT. Immunohistochemistry was performed on paraffin sections using monoclonal antibodies to CD34 (QBEND/10), vimentin and GCDFP-15. CD34 was also tested in seven cases of basal cell carcinoma (BCC), three with outer root sheath differentiation and four with morphea-form features, and five squamous cell carcinomas. Histologically, features of conventional trichilemmoma were seen at the periphery of the seven lesions. In contrast, at the center, the epithelial cells tended to cluster in narrow irregular cords and nests entrapped in a dense collagenous stroma. One case of DT coexisted with a BCC. In all cases of DT, epithelial tumor cells showed CD34 immunostaining. All cases of BCC, including the one contiguous to a DT, were CD34 negative. CD34 immunodetection in the epithelial cells of the pseudoinvasive component of DT may be of great value in the differential diagnosis with other desmoplastic tumors of the skin, and particularly with BCC.

An 8-year-old girl had small, papular vulval lesions for six years; the lesions were yellowish with numerous surface depressions. Symptoms due to the action of mastocyte mediators were observed. A biopsy specimen showed a dense monomorphous infiltrate of the deep dermis by rounded cells with granular cytoplasm and a round or oval central nucleus. The morphology of the lesions and red-purple metachromatic staining led to the diagnosis of xanthelasmoid mastocytosis. Symptoms were controlled with hydroxyzine. Annual follow-up has shown no evidence of systemic involvement to date. Surgery should be contemplated as a future therapeutic option, in view of the location of the lesions.

This case may be considered a new variant of perineurioma with Pacinian-like features, for which we propose the designation 'sclerosing Pacinian-like perineurioma'.

No abstract