Rhabdomyomatous Mesenchymal Hamartoma Presenting as a Skin Tag in the Sternoclavicular Area

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital lesion of the dermis and subdermis. It has been described predominantly in newborns, with 30 cases reported in the English literature. Typically, it appears as a skin tag, papule, nodule or a mass involving the face or sternal notch. A 28-day-old girl presented with a 1.4×0.8 cm soft skin tag in the right sternoclavicular area. Physical examination revealed no congenital anomalies. A shaved biopsy showed that the core of the lesion contained striated muscle fibers mixed with hair follicles and sebaceous and eccrine glands. Thin epidermis lined the outside of the tag. We report a patient with a RMH in a site not previously reported and discuss the differential diagnosis.