Rhabdomyomatous Mesenchymal Hamartoma: Expanding the Histological Spectrum of This Rare Congenital Entity

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare, benign lesion composed of disorganized skeletal muscle and mesenchymal elements within the dermis and subcutis. It typically arises in midline locations of the head, neck, and trunk during infancy or early childhood. The full histopathologic spectrum of RMH remains incompletely characterized. We present 4 cases of RMH, including 1 with a previously unreported fibrocartilaginous component-highlighting a novel histologic finding. Clinical impressions varied, and RMH was not considered in any of the cases. This series expands the known morphologic range of RMH and emphasizes its potential to mimic other developmental lesions. Recognition of its distinct features may help avoid unnecessary interventions in pediatric patients.