13. Tumors of the Nail Apparatus and Adjacent Tissues

Summary

Many tumors are encountered in the nail unit. All components of the nail apparatus produce tumors that exhibit benign behavior in the vast majority of cases. However, the malignant counterpart of every tumor type also exists. Tumors of the nail unit may correspond to tumor types also present elsewhere on skin such as warts, nevi, melanoma and squamous cell carcinoma. In this case their clinical presentation is often influenced by the anatomy and physiology of the nail: longitudinal bands, subungual tumoral syndrome. Some tumors are also present on the rest of skin but are more frequent on the nail unit, such as glomus-cell tumor. Lastly, some tumors are quite specific to the nail unit either because they derive from an adjacent structure that influences the nail plate outgrowth, such as exostoses enchondromas, or because they derive from a nail-specific tissue, such as onychomatricomas. All these particularities of nail apparatus tumors create a specific semiology (melanonychia striata, for example) and often a specific diagnostic strategy (dermoscopy, magnetic resonance imaging, specific biopsy techniques) and, in many cases, a site-specific treatment (conservative melanoma surgery, for example).