Smooth muscle hamartoma and striated muscle hamartoma: Clinicopathologic characterization of two rare entities and literature review

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

ABSTRACT

Rhabdomyomatous mesenchymal hamartoma (RMH) typically presents as a congenital midline head and neck cutaneous polyp in infants. Perianal and mucocutaneous lesions have been reported, and recently, acquired adult-onset variants have been proposed. This makes the true prevalence, etiopathogenesis, and clinicopathologic distribution and classification of RMHs in children compared with those in adults uncertain. We performed a retrospective review to highlight the salient histopathologic, histochemical, and immunohistochemical features in RMHs and to emphasize their specific clinicopathologic criteria to avoid diagnostic pitfalls. We found 4 (0.3%) infants [2 female infants and 2 male infants, average age: 4 months] with mental, nasal, lingual, and perianal midline RMHs (average size: 1.0 cm) of 1303 patients with cutaneous polypoid lesions. Three were isolated, and 1 was associated with Goldenhar syndrome. The cutaneous polyps demonstrated intermixed skeletal muscle, adipose, and fibrocollagenous core stroma that extended into the dermis and around the dermal appendages. The lingual lesion demonstrated skeletal muscle and fibrocollagenous stroma with prominent nerve bundles and little adipose tissue. All showed interstitial loose mesenchyme. Masson trichome demarcated the triphasic stromal components. Alcian blue demonstrated the loose myxoid mesenchyme. Elastic van Gieson did not show elastic fibers. Desmin demonstrated the skeletal muscle bundles, S100 highlighted the adipose tissue lobules and the nerve bundles, and CD34 displayed the mesenchymal stroma. Ki67 showed a low proliferation index in the loose mesenchyme. Smooth muscle actin did not reveal smooth muscle bundles, but with CD31, they highlighted the thick blood vessels. CD117 revealed prominent mast cells. From our retrospective review series, 4 cases that originally diagnosed as RMHs were excluded. Likewise, we found some examples of the reported cases in the English literature that might have been mistaken for RMHs. This is because they did not fulfill the diagnostic clinicopathologic criteria. RMH constitutes a rare entity with specific clinicopathologic features. Most lesions are isolated. Some are associated with congenital anomalies and syndromes. Strict clinicopathologic diagnostic criteria should be applied to avoid mislabeling look-alike lesions for RMHs.

Presentation of a Smooth Muscle Hamartoma in the Bulbar Conjunctiva of an Adolescent Boy: A Case Report and Review of Literature

PURPOSE

The aim of this study was to describe a novel presentation of conjunctival smooth muscle hamartoma and review the histopathologic findings of this entity.

METHODS

A 17-year-old African American adolescent boy presented with a pink, nontender lesion of the right bulbar conjunctiva that did not improve with medical management. He had no previous medical or ocular history. The lesion was excised.

RESULTS

Histopathologic examination disclosed morphologically benign smooth muscle bundles within the substantia propria that stained positively for smooth muscle actin, vimentin, and desmin consistent with the diagnosis of a smooth muscle hamartoma.

CONCLUSIONS

Although congenital smooth muscle hamartomas of the conjunctiva have been rarely reported in the literature, this is the first described case of a smooth muscle hamartoma presenting in adolescence in the bulbar conjunctiva. This lesion should be considered in the differential diagnosis for adolescents with similar appearing lesions.

Rhabdomyomatous mesenchymal hamartoma presenting as telangiectasia in a 57-year-old man

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare congenital malformation of the dermis and subcutaneous tissue. Usually, RMH occurs in the midline of the face and neck region. We described a case of RMH presenting as telangiectasia in a 57-year-old man with a history of pityriasis lichenoides chronicus. Histopathological examination revealed a subepidermal haphazard proliferation of striated muscular tissue perpendicular to the epidermis. These bundles of striated muscular tissue were admixed with adnexal structures. The diagnosis was consistent with RMH. RMH is more common in the neonatal period or in young children, but we should consider it as part of a differential diagnosis in older adults as well.