Jorge Mora-Constantino, Department of Radiology and Imaging, CADEM del Moral, Laboratorios Chopo, Mexico City, Mexico
Esteban Barbosa-Peña, Department of Radiology and Imaging, Specialty Hospital Num.1, Centro Medico Nacional del Bajio, Instituto Mexicano del Seguro Social. Leon, Guanajuato, Mexico
Victor M. Pulido-Cheverria, Department of Radiology and Imaging, Specialty Hospital Num.1, Centro Medico Nacional del Bajio, Instituto Mexicano del Seguro Social. Leon, Guanajuato, Mexico
Roberto Hernandez-Juarez, Department of Radiology and Imaging, Hospital Angeles Pedregal; Facultad de Medicina, Division de Posgrados, Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
The reversed palmaris longus muscle (RPLM) is an uncommon anatomical variant that can mimic a space-occupying lesion of the forearm. We present the case of a 13-year-old boy, a competitive martial arts, with a painful mass in the right forearm. A high-resolution musculoskeletal ultrasound (MSK-US) exhibited an ovoid muscle structure, isoechoic to adjacent muscles, with a typical fibrillar pattern, anomalously located in the distal third of the right forearm. The RPLM showed an inverted morphology, with a distal muscle belly and a proximal tendon. This anatomical variant is positioned adjacent to the median nerve (MN), resulting in local compression. Real-time dynamic MSK-US demonstrated thinning of the muscle belly during active contraction. Color and power Doppler US showed normal intrinsic vascularity and excluded neoplastic or inflammatory processes. A contralateral examination showed a normal palmaris longus tendon in the left forearm. An anterior right forearm RPLM was diagnosed by MSK-US. Management was conservative, focusing on patient education, physical therapy emphasizing stretching and strengthening, and a temporary reduction in martial arts practice intensity. This case report provides a detailed description of an RPLM diagnosed by MSK-US, highlighting its utility as a dynamic, accessible, and high-resolution tool.
Keywords: Reversed palmaris longus muscle. Musculoskeletal ultrasound. Median nerve. Anatomical variants. Nerve entrapment syndrome. Case report.
