Rhabdomyomatous mesenchymal hamartoma presenting as a sacral skin tag in two neonates with spinal dysraphism.

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital malformation involving the dermis and subcutaneous tissue, of which there were 62 reported cases through 2014. We report RMH in two neonates presenting as a sacral skin tag. In both cases, magnetic resonance imaging (MRI) of the spine showed evidence of spinal dysraphism, including a lipomyelomeningocele and a tethered cord. Surgical repair of the defects was performed. Histopathologic examination of the skin tags showed a haphazard arrangement of mature skeletal muscle fibers and adnexal elements, consistent with RMH. The second patient also had a hemangioma on the sacrum and was diagnosed with LUMBAR (lower body hemangioma and other cutaneous defects, urogenital anomalies/ulceration, myelopathy, bony deformities, anorectal/arterial anomalies, and renal anomalies) syndrome, an association between cutaneous infantile hemangiomas of the lower body and regional congenital anomalies. The apparent association of paraspinal RMH with spinal dysraphism suggests that aberrant migration of mesodermally derived tissues (including skeletal muscle fibers) during neural tube development may be responsible for the pathologic findings in the skin. Additional study of patients with spinal dysraphism and congenital cutaneous lesions may further support this hypothesis.