Rhabdomyomatous mesenchymal hamartoma of skin.

A distinctive dermal and subcutaneous hamartoma composed primarily of disorganized skeletal muscle and mature adipose tissue, designated rhabdomyomatous mesenchymal hamartoma of skin, was recently reported. We have observed two histologically similar though less polypoid lesions in boys aged 4 years. Both were also on the chin and present since birth, suggesting that site and age, as well as histology, may be characteristic. The location on the chin in three of the four neonates may reflect an etiology of aberrant embryologic development of the platysma muscle as it inserts superficially into the dermis over the mandible.