Reversed palmaris longus forming a mass in the distal forearm

The palmaris longus muscle has significant anatomical variance compared to other muscles of the upper extremity. The most frequent variation is the complete absence of the muscle, but a number of other variations exist. These variations include reversed, duplicated, bifid, or hypertrophied palmaris longus muscles. Anomalous muscles usually do not cause pathologic symptoms, but are a diagnostic dilemma. They become a surgical problem when they cause symptoms or are difficult to differentiate from soft-tissue masses. This article describes the presence of a reversed palmaris longus muscle in a 21-year-old man, diagnosed during exploration of the soft tissue mass on his right forearm.