dermatofibroma, Neurofibroma
Dermatofibroma Dermatofibroma - A slowly-growing, benign skin papule, nodule or tumor that usually has overlying hyperpigmentation. Dermatofibromas clinically exhibit the " dimple sign ," and are the most common growth below the knee in young adults. The true etiology of a dermatofibroma is unknown, but the lesions are thought to arise at sites of prior trauma or as a late histiocytic reaction to an arthropod bite. Microscopic appearance shows a cellular proliferation of spindled cells in the dermis which has an irregular outline and at the periphery, entraps and surrounds the (normal) thickened (“keloidal”) dermal collagen bundles. The cells may appear as fibrocytes, lipid laden histiocytes, and multinucleate histiocytes sometimes containing hemosiderin pigment. These benign dermal proliferations can induce overlying epidermal proliferation. The basal epidermal layer is classically hyperpigmented. It is also known as a fibrous histiocytoma. Clinical: dermatofibroma ...