Absence of musculocutaneous nerve associated with the presence of an accessory head of the biceps brachii muscle: report of a bilateral case and its clinical implications

The anatomical variants of the biceps brachii muscle (BBM) are frequent, mostly unilaterally than bilaterally, and are associated with supernumerary muscle bellies, the total absence of the muscle or one of its heads, and variations in the points of origin and insertion. In the same way, the variants of the musculocutaneous nerve (MCN) can include alterations in its course, number of branches, or anatomical relations, whereas its absence is considered an atypical variation. The aim of this work was to report the absence of musculocutaneous nerve associated with the presence of one accessory head of the biceps brachii muscle. Dissection of a female cadaver, fixed in 10% buffered formaldehyde, which did not present previous surgeries in the studied area was performed. Variations were noted in both upper limbs related to accessory muscle bellies and change in innervation. Anatomical relations of muscles and nerves were determined by following proximal to distal ends, relation, vascularization, and innervation pattern. The absence of MCN associated with the presence of one accessory head of the BBM were found bilaterally. These anatomical variations are atypical. Clinically, these variations can produce compressive symptoms that could generate confusing diagnostics and conduce to unnecessary procedures on the arm, inducing iatrogenic actions.