Atlas of Diagnostic Pathology (7) : Skin: Tumors of Cutaneous Appendage

This article will deal exclusively with cutaneous adnexal tumors. From the viewpoint of diagnosis of adnexal tumors, embryologic and histologic considerations will be given priority. A good understanding of hair germ structure and normal histology of the hair follicle, which comprises the hair matrix (matrical cells), the inner and outer root sheaths, isthmus and infundibulum, is a fundamental need in managing follicular diseases. Hair germrelated benign tumors are trichoblastoma and trichoepithelioma, their malignant counterpart being basal cell carcinoma (epithelioma). Calcifying epithelioma is a tumor closely related to the hair matrix (matrical cells) and so has recently been termed "pilomatrixoma". In sebaceous lesions, it is essential to detect sebocytes and the sebaceous duct. In contrast to sebaceous hyperplasias, sebaceous neoplasms always exhibit seboblast proliferation. In sebaceous carcinoma, the sebaceous differentiation is sometimes obscured. A sweat "gland" tumor actually shows sweat "duct" differentiation with a glandular structure consisting of inner cuticular cell and outer poroid cell linings. Poroma is a neoplasm consisting of pores covered by cuticular cells. Its poroid cells proliferate, mimicking normal acrosyringium. Cutaneous mixed tumor, the tumors include differentiation towards a hair follicle, bone, cartilage, fat, etc. In this case, a "mixed tumor" is truly mixed