Not Your Average Skin Tags: Multiple and Lateral Rhabdomyomatous Mesenchymal Hamartomas in an Infant

Summary: Rhabdomyomatous mesenchymal hamartomas (RMH) are rare, benign congenital lesions characterized by the disorganized proliferation of mesenchymal tissues within the dermis and subcutaneous tissue. These lesions typically present as solitary, midline growths in the head and neck region of infants and are often misdiagnosed as skin tags. We report a unique case of an 8-month-old with multiple RMH presenting as peri-auricular skin growth on the cheek. Clinical examination revealed three distinct exophytic lesions, including sessile and pedunculated, as well as a subcutaneous nodules. Histologic examination of the resected lesions demonstrated multiple cutaneous polyps containing intermixed skeletal muscle, adipose tissue, and fibrocollagenous stroma, consistent with RMH. Histologically, RMH exhibits distinctive features that can mimic other cutaneous hamartomas of infancy. However, some previously reported cases may have been misclassified as RMH due to insufficient adherence to diagnostic clinicopathologic criteria, or a failure to consider RMH due to the rarity of the condition. While most RMH lesions occur in isolation, a subset is associated with congenital anomalies and syndromes. Therefore, strict diagnostic criteria are crucial to accurately differentiate RMH. This case represents a rare instance of multiple RMH in a pediatric patient and underscores the importance of recognizing the varied presentations of this entity.