Cutaneous intramuscular lipoma: A new subtype of intramuscular lipoma.

Intramuscular lipoma is an uncommon variant of lipoma that occurs inside muscle tissue. Pathogenesis is thought to be related to neoplastic activity of mesenchymal stem cells, but there still is not an established theory. This entity can be found in almost all areas of the body, mostly within or in connection with skeletal muscle tissue. We have encountered an atypical intramuscular lipoma located in the epidermal layer of the right thigh of an otherwise healthy 35-year-old female. The superficial, protruding skin mass resembled a sebaceous nevus or skin malignancy but was histologically composed of well-defined adipocytes between a mixture of muscle fibers, corresponding with the diagnosis of intramuscular lipoma. Intramuscular lipoma of the skin has never been reported before; thus, the authors suggest the classification "cutaneous" intramuscular lipoma to describe lesions located in the dermal or epidermal layer.