Plaque-Type Variant of Acquired Rhabdomyomatous Mesenchymal Hamartoma on the Chin: A Case Series.

Rhabdomyomatous mesenchymal hamartoma (RMH) is a rare benign tumor composed of skeletal muscle fibers and other mesenchymal-derived cells. The lesions are generally solitary sessile papules or skin tag lesions that occur during childhood. We retrospectively reviewed patients diagnosed with RMH pathologically between January 2001 and June 2020 at a tertiary medical center. A literature review was conducted. Seven plaque-type RMHs on the chin were found, including 6 in adults and one in a 14-year-old boy. The average age was 45.7 years. The onset of the RMH appearance was between several months and years. Pathologically, all patients showed a scattered haphazard arrangement of skeletal muscle bundles in the dermis and/or subcutis. Subcutis replaced by fibrous tissue and skeletal muscle bundles was present in 2 cases. Some skeletal muscles had a periadnexal distribution. This case series demonstrated a distinct clinical presentation of acquired RMH specifically located on the chin.