Solitary familial desmoplastic trichoepithelioma. A study by conventional and electron microscopy

Solitary desmoplastic trichoepitheliomas from a mother and two daughters were studied by conventional and electron microscopy. Differential diagnosis by conventional microscopy is briefly discussed. The lesions consisted of cords and nests of basaloid cells set in fibrotic stroma and confined to the dermis. In addition, each lesion contained horn cysts and focal areas of calcification. Horn cysts were occasionally identified in continuity with infundibulae of normal hair follicles. Semithin sections showed cords and nests of cells in continuity with the horn cysts. Ultrastructurally, a continuous basal lamina surrounded the cords of basaloid cells and connected to horn cysts. Individual cells contained tonofilaments and were attached to adjacent cells by desmosomes. Hemidesmosomes were present at peripheral cell membranes bounded by basal lamina. There was no glandular differentiation. Our observations by electron and conventional microscopy support a conclusion that desmoplastic trichoepitheliomas are derived from hair appendages.