Morphologic Spectrum of Rhabdomyomatous Mesenchymal Hamartomas (Striated Muscle Hamartomas) in Pediatric Dermatopathology

Abstract

Background:Rhabdomyomatous mesenchymal hamartomas (RMHs), also termed striated muscle hamartomas, are rare benign tumors of skin and subcutis, which mostly occur at birth with a predilection for the head and neck. Simple surgical excision is the treatment modality of choice with excellent prognosis.Objective:To review the spectrum of the different clinical and pathologic features of RMHs in pediatric patients and recognize their characteristics to avoid confusion with other lesions in their list of differential diagnosis.Methods:Six cases of RMH diagnosed at our institution from 2009 to 2021 were retrieved from our files and reviewed retrospectively after anonymization by an honest broker. This review is IRB-approved by the University of Pittsburgh School of Medicine, study STUDY19080192.Results:The patients' age ranged from 6 days to 8 years, with a female predominance (2:1). In all cases, the lesion was present at birth. All lesions, except for 2, occurred in the head and neck regions. One patient had multiple additional small nodules in the face, whereas all others presented with solitary RMHs. The size of the lesions varied, and their composition included bundles of skeletal muscle (the landmark finding) associated with variable amounts of adipose, fibrous, vascular, nerve, and adnexal structures.Conclusions:RMH is a benign hamartomatous lesion with a variable phenotypic spectrum. RMHs predominate in the head and neck. Familiarity with these lesions, including their presentation in less frequent anatomical sites, is important to avoid diagnostic misinterpretations and potential overtreatment. This study represents one of the largest series of RMHs in the literature, including an unusual case in a perianal location.

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

“…RMH, alternatively labeled as striated muscle hamartoma or midline congenital hamartoma, typically manifests as a single polypoid lesion of the skin and subcutaneous tissue with characteristic clinicopathologic features. 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,[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. 7,8,22 Most cutaneous and mucocutaneous lesions occur in infants, young children, and teenagers as isolated nonenlarging polypoid lesions.…”

“…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.…”

“…Despite being initially considered a rare distinct congenital clinicopathologic entity, rhabdomyomatous mesenchymal hamartoma (RMH) remains a controversial lesion because its prevalence, etiopathogenesis, and clinicopathologic distribution and classification in children compared with those in adults are not yet clearly elucidated. [1][2][3][4] Even though it classically presents as a midline head and neck polypoid cutaneous nodule in neonates and infants, increasingly perianal and mucocutaneous polypoid lesions and recently acquired adult-onset plaque variants have been described in adults. 1,[4][5][6][7][8][9][10] In addition, some of the reported cutaneous and mucocutaneous polypoid lesions might have been mistaken for RMHs.…”

“…[1][2][3][4] Even though it classically presents as a midline head and neck polypoid cutaneous nodule in neonates and infants, increasingly perianal and mucocutaneous polypoid lesions and recently acquired adult-onset plaque variants have been described in adults. 1,[4][5][6][7][8][9][10] In addition, some of the reported cutaneous and mucocutaneous polypoid lesions might have been mistaken for RMHs. We report 4 cases of chin, nose, tongue, and perianal midline RMHs in infants.…”