Vulvar trichogenic tumors: a comparative study with vulvar basal cell carcinoma.

Trichogenic tumors are very rare in genital skin and often cause diagnostic problems because they are mitotically active and they share some histologic features with basal cell carcinomas (BCCs). We present the clinical and histologic features of 16 vulvar trichogenic tumors (6 plaque-like, 10 nodular; average age, 65 years) in comparison with 16 BCCs (11 plaque-like, 5 nodular; average age, 78 years). All trichogenic tumors, except 1 case with HSV infection, were nonulcerated tumors. Superficial plaque-like trichogenic tumors featured basal keratinocyte proliferations with peripheral nuclear palisading but no clefting at the epithelial-stromal interface. Nodular trichogenic tumors consisted of solid lobules of squamous cells and anastomosing cords and reticulations of follicular germinative cells with mitoses and apoptosis. Large pink cells with trichohyaline granules and melanocytes resembling the inner hair sheath, and clear cells resembling the outer root sheath were common. Most cysts were keratinized, but some fluid-filled cysts showed apocrine and sebaceous differentiation. The well-defined mesenchymal component of trichogenic tumors was pale and mucinous, and contained fibrocytes and fibrillary collagen bundles. All BCCs showed surface ulcerations and clefting at the stromal-epithelial interface. BCCs showed no trichogenic differentiation and lacked an organized mesenchymal tumor component. The tumor stroma of BCCs was paucicellular, mucinous, or granulation tissue-like with an inflammatory infiltrate.