The brachioradialis longus: an unreported accessory form of the brachioradialis muscle.

The brachioradialis muscle (BR) belongs to the lateral forearm muscle. Typically, the radial nerve innervates it. BR morphological variability, such as split muscular belly, split tendon, or accessory BR (ABR), has been described in the current literature. A 68-year-old female donated cadaver was routinely dissected for research and educational purposes. A variant muscle was identified extending at the right arm's lateral and forearm compartments. It originated from the humerus lateral surface between the deltoid and the triceps brachii lateral head, joined the second muscular head from the brachialis muscle, and inserted into the radius styloid process. According to its origin, course, and insertion, the variant muscle probably corresponded to the BR accessory form. However, in the current literature, the ABR morphology corresponds to an accessory muscle originating adjacent to the typical BR and inserted into the radial tuberosity. At the same time, it was defined as "brachioradialis brevis." In the current case, the variant muscle differed significantly from the current literature due to the origin, insertion, length, and relationship with the typical BR; therefore, the term "brachioradialis longus" seemed adequate to describe this variant muscle.