A negligible diagnosis: Rhabdomyomatous mesenchymal hamartoma

Rhabdomyomatous mesenchymal hamartoma is a rare lesion of the dermis and subdermal tissue. It was first described in 1986 as “striated muscle hamartoma”. It has been usually reported in newborns. Until recently, there were only 34 reported cases in the literature.We herein report a three-month-old boy with a congenital skin tag in the middle of the chin. Physical examination revealed no congenital abnormalities or other dermal lesions. Histopathological examination showed a mixed tissue collection of subepidermal disorganized skeletal muscle fibers, adipose, fibrous and neural tissues, and abundant folliculosebaceous structures.Clinically, the differential diagnosis of rhabdomyomatous mesenchymal hamartoma includes skin tag, accessory tragus and soft fibroma. If the presence of striated muscle fibers has been ignored, there is microscopic resemblance between all of these lesions. Because of the absence of recurrence or malignant degeneration, this lesion may be accepted a negligible diagnosis. But for as many as 30% of the reported cases with rhabdomyomatous mesenchymal hamartoma have several congenital anomalies; the differential diagnosis of this lesion is important.