ABSTRACT
Epithelial, fibroepithelial, fibrous and other mesenchymal, vascular, neurogenic, hematogenous, melanocytic, and metastatic tumors plus a variety of reactive and degenerative pseudotumorous lesions occur in and around the nail unit. There are a variety of malignant neoplasms of the nail apparatus with melanoma, Bowen's disease, and squamous cell carcinoma being the most common. This chapter discusses the histopathology and differential diagnosis of some of the benign epithelial and fibroepithelial tumors, such as viral warts, seborrheic keratosis, subungual linear keratotic melanonychia, onychocytic acanthoma, subungual filamentous tumor, onychopapilloma, localized multinucleate distal subungual keratosis and subungual warty dyskeratoma. It also discusses the histopathology and differential diagnosis of some of the keratinocytic precancers, in situ carcinoma, and carcinomas, such as actinic keratosis, arsenical keratosis, Bowen's disease, squamous cell carcinoma, carcinoma cuniculatum, basal cell carcinoma, onychocytic carcinoma, onycholemmal carcinoma and aggressive digital papillary adenocarcinoma.
