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Case Reports

Abstract

Rhabdomyomatous mesenchymal hamartoma (RMH), also referred to as striated muscle hamartoma, is a rare, benign congenital lesion characterized by an irregular proliferation of mature skeletal muscle within the dermis and subcutaneous tissue. These lesions often contain a mixture of other mesenchymal components, including adipose tissue, blood vessels, and peripheral nerves. RMH typically appears as a solitary, midline mass on the head or neck and is most frequently diagnosed at birth or during early infancy. In this report, we present a rare case involving a 14-year-old female who developed a painful, slowly enlarging mass inside her right nostril. On physical examination, a 3.0 × 3.0 mm sessile lesion with an underlying cystic component was identified along the medial intranasal border of the right columella. The lesion was completely excised, and subsequent histopathologic examination revealed disorganized bundles of skeletal muscle intermixed with adipose tissue and adnexal structures within the dermis, confirming the diagnosis of RMH. This case is particularly unusual due to the patient’s age, the lesion’s intranasal location, and the presence of pain, features that deviate from the classical presentation. Although perianal and mucocutaneous RMHs have been described, acquired or adult-onset variants remain extremely rare and poorly characterized.  Accurate diagnosis hinges on complete surgical excision as diagnosis relies on deep histologic assessment, as superficial biopsies may miss defining features. This case underscores the importance of considering RMH in the differential diagnosis of polypoid cutaneous nasal masses across all age groups and  when the clinical picture falls outside of the expected pattern.