Rhabdomyomatous Mesenchymal Hamartoma Presenting as a Midline Nasal Papule in Early Infancy: Case Report

Hamartomas are benign, tumor-like malformations composed of an abnormal mixture of tissue elements normally found at the site of origin but arranged in a disorganized fashion. Rhabdomyomatous Mesenchymal Hamartoma (RMH) is a rare subtype, first described in 1986, characterized by a haphazard proliferation of mature skeletal muscle fibers admixed with other mesenchymal and adnexal elements within the dermis and subcutis. RMH most commonly presents as a congenital, solitary, dome-shaped papule or nodule in the midline head and neck region of infants and young children, though cases in older children and adults, as well as in atypical locations, have been reported. We present the case of a 2-month-old female with a congenital midline nasal lesion that enlarged proportionally with growth. Physical examination revealed a firm, dome-shaped papule on the inferior columella. MRI and MRA excluded intracranial extension. Surgical excision at 14 months demonstrated haphazardly arranged skeletal muscle bundles within the dermis, interspersed with hair follicles and adipocytes with desmin positivity and SMA negativity on immunohistochemistry, confirming the diagnosis of RMH. Surgical excision remains curative with no reported recurrences or malignant transformation. This case highlights the importance of considering RMH in the differential diagnosis of midline facial papules in infants and demonstrates the value of clinicopathologic correlation and imaging to guide management.