18618 A differential diagnosis for the congenital midline mass: Striated muscle hamartoma
Zarbo A, Luk KM, Friedman BJ, and Shwayder T. 18618 A differential diagnosis for the congenital midline mass: Striated muscle hamartoma. Journal of the American Academy of Dermatology 2020; 83(6):AB216.
J Am Acad Dermatol
History: A 5-day-old black male full-term neonate born via vacuum-assisted delivery for non-reassuring fetal heart rate presented with congenital presentation of two asymptomatic midline lesions which appeared asymptomatic. There was no history of seizures, ophthalmologic findings, abnormalities in head circumference, height, weight, or limb size. Newborn screening examination was unremarkable. Examination: On the midline submental chin there was a soft, brown dome-shaped plaque measuring 0.8 cm with a circumferential ring of light brown pigmentation; on the midline upper chest there was a light brown 2-mm dome-shaped papule. Course and Therapy: Ultrasound of the submental chin lesion revealed a 0.5 × 0.8 × 0.4-cm heterogeneously hypoechoic structure with a peripheral soft tissue rind. Punch biopsies of the submental chin and the midline upper chest revealed haphazardly arranged striated muscle fibers in the dermis, some of which inserted directly into the epidermis. The muscle fibers were highlighted by Masson trichrome and myogenin. Alcian blue revealed increased dermal mucin. Discussion: Striated muscle hamartomas (SMH) are rare, benign congenital skin tumors characterized by haphazard arrangement of mature striated skeletal muscle, collagen, nerve bundles, and adipose tissue in the dermal and subcutaneous tissue. Although a rare entity, it is important to recognize this benign hamartoma as a congenital midline defect. Conservative management with clinical monitoring is recommended if cosmetically acceptable, as spontaneous regression over a period of years has been reported. Surgical excision may be pursued; however, the hamartoma may recur.