Clinical history: 25 year old male with hyperpigmented 0.8cm painless papule on back.
What is the most probable diagnosis?
The dermatofibroma is the most common form of benign fibrous histiocytoma. These tumours are formed by benign, spindle=shaped cells arranged ina well-defined, nonencapsulated mass within the mid-dermis.
Extension of these cells into the subcutaneous fat is sometimes observed. Many cases demonstrate a peculiar form of overlying epidermal hyperplasia, characterized by downward elongation of hyperpigmented rete ridges.
Numerous histologic variants are noted, such as more cellular forms or tumours with pools of extravascular blood and hemosiderin.