BENIGN TRICHOGENIC TUMORS - A REPORT OF 2 CASES SUPPORTING A SIMPLIFIED NOMENCLATURE

We report two cases of a rare benign tumour of hair germ. Clinically, both were solitary, well-circumscribed, subcutaneous nodules located i n the extremities. Histologically, the tumours were characterized by n ests and thin cords of basaloid epithelial cells intimately associated with a cellular stroma. The basaloid cells exhibited peripheral palis ading, keratinization in the form of keratotic cysts and squamoid tran sformation, and pilar differentiation. An unusual, but distinctive, cr ibriform pattern of growth was observed. There was no communication wi th the overlying epidermis. Abundant primitive hair germinal buds and rare more advanced abortive hair follicles were identified. These hist ological appearances encompass features of both trichoblastic fibroma and trichogenic trichoblastoma, thus distinguishing these neoplasms fr om other skin tumours and reinforcing the hypothesis that these tumour s are closely related from a histogenetic point of view. The presence of overlapping histological features can be problematic for practising histopathologists who rarely encounter these conditions. With this in mind, the term benign trichogenic tumour may be more appropriate to e ncompass these two tumours and related neoplasms that appear to lie wi thin the spectrum of hair follicle development.