Coexistence of tumor of the follicular infundibulum with an unusual trichilemmal tumor.

Tumor of the follicular infundibulum (TFI) is a rare epithelial tumor, and its histogenesis is still somewhat debatable. The diagnosis of TFI cannot currently be made before biopsy, and it is most often misdiagnosed as basal cell carcinoma (BCC). A 78-year-old woman presented to the dermatology clinic with a slightly erythematous nodule surrounded by fine telangiectasia on her right temple. Histopathologic examination of the lesion revealed an epithelial tumor with a plate-like growth pattern as is typical of TFI. In the same specimen, an unusual trichilemmal tumor with multiple epidermal connections was observed adjacent to the foci of TFI. The lobular tumor was composed of a large mass of keratinocytes with pale cytoplasm arranged as sheets and interconnecting ribbons. Several cells with hyperchromatic nuclei and small foci of compact cornification were also noted within the bulk of the tumor. The histopathologic features of the unusual tumor were reminiscent of BCC with trichilemmal differentiation or desmoplastic trichilemmoma.