Rhabdomyomatous mesenchymal hamartoma presenting as a chin nodule in a 15‐year‐old male

Abstract

Rhabdomyomatous mesenchymal hamartoma (RMH), also known as congenital midline hamartoma and striated muscle hamartoma, is a rare congenital malformation presenting most commonly in midline sites of the head and neck region. Since its first description in 1986, 67 cases have been reported to date. We report a case of RMH presenting as a chin nodule in an otherwise healthy 15‐year‐old male. The patient presented with a dome‐shaped subcutaneous lesion on his chin which had been present since birth, but had grown and was interfering with his ability to shave. He otherwise had no history of congenital anomalies or malformations. Histopathological examination of the excised lesion revealed a haphazard proliferation of striated muscle admixed with adipose tissue and adnexal structures within the dermis and subcutaneous tissue, consistent with a diagnosis of RMH. While the majority of reported cases are of newborns or children under 3 years of age, RMH may not come to clinical attention until later in life. This rare malformation should be included in the differential diagnosis of lesions containing dermal striated muscle and/or adipose tissue, to include nevus lipomatosus superficialis, fibrous hamartoma of infancy, neuromuscular choristoma, fetal rhabdomyoma, and rhabdomyosarcoma.

Rhabdomyomatous Mesenchymal Hamartoma: Report of 4 Cases With Histochemical and Immunohistochemical Findings and Emphasis on Potential Pitfalls

“…1,2,[20][21][22] The cutaneous lesions have a predilection to the head and neck region, particularly the midline area of the chin and nose. 1,4,[22][23][24] Collectively, congenital perianal polypoid lesions constitute the second most common site for RMHs in neonates and infants. 1,4,6,7,25 Other mucocutaneous sites include the oral cavity, nasal cavity, and vagina.…”

“…Central congenital solitary static polypoid lesions occurring in children and showing prominent disorganized skeletal muscle bundles within the dermis intermixed with mesodermal and ectodermal elements are clinical and histopathologic prerequisites. [1][2][3]6,[20][21][22][23][24] Multiple forms are rare. 1,7,22,27 A mixed myogenous variant hamartoma composed of skeletal and smooth muscle tissues has been described.…”

“…Central congenital solitary static polypoid lesions occurring in children and showing prominent disorganized skeletal muscle bundles within the dermis intermixed with mesodermal and ectodermal elements are clinical and histopathologic prerequisites. 1–3,6,20–24…”

“…7,8,22 Most cutaneous and mucocutaneous lesions occur in infants, young children, and teenagers as isolated nonenlarging polypoid lesions. 1,6,8,[22][23][24]26 Some have been found to be associated with a variety of syndromes and congenital anomalies. 3,22,27 The correct diagnosis requires strict clinicopathologic criteria.…”