Question:

A 30-year old gentleman presented with a small brownish cutaneous nodule over his right thigh for two years. It remained static in size and asymptomatic. Physical examination revealed a firm 0.6cm diameter brownish, oval cutaneous nodule. There was neither surface scaling nor tenderness. There was no punctum and protruding hair and the mass was not attached to underlying structure.

Answer: A. Dermatofibroma

Dermatofibroma is a common benign cutaneous tumour of mesenchymal origin. Histologically, spindle-shaped fibroblastic cells, arranged in a haphazard pattern, are found beneath an acanthotic epidermis. Dermatofibroma usually presents as solitary brownish nodule over the extremities with variable epidermal scaling. Fluctuation sign is absent as it is composed of solid mass of fibroblastic cells. The brownish appearance is secondary to the deposition of melanin in basal epidermal cells. It is a benign condition and can be treated by surgical removal. Recurrence may sometimes be present after removal as the tumour does not have a well defined capsule.

Epidermoid cyst is a common benign cystic lesion with its capsule composed of stratified squamous epithelium. Clinically, it appears as a round cutaneous nodule. When it is large enough, sign of fluctuation can be elicited. Punctum, when present, is highly suggestive of epidermoid cyst. Steatocystoma is benign cystic condition with its wall composed of keratinizing epithelium with areas of sebaceous lobules. Steatocystoma, when multiple, usually appears on the chest wall and the scrotum, a condition known as steatocytoma multiplex. Clincally, they appear as dermal nodules which are skin-coloured. But in areas with thin epidermis like the scrotum, a whitish complexion may be noted. Junctional melanocytic nevus has two components- dermal and epidermal. While the dermal clusters of nevus cells give rise to a raised clinical appearance, the epidermal counterpart causes a speckled pigmentation on the surface. Protruding hair on the mass, when present, is suggestive of melanocytic nevus.