ABSTRACT
Anatomic variations in the anterior aspect of the shoulder, such as an accessory head of the biceps brachii muscle, are not uncommon. The magnetic resonance imaging and arthroscopic appearance of the accessory head of the biceps brachii has been recently described. This series demonstrates the sonographic appearance of the accessory head of the biceps brachii in the bicipital groove. It is an asymptomatic, flat, echogenic structure with average measurements of 7.7 × 1.2 mm in cross section. Knowledge of this anatomic variant can avoid the misdiagnosis of a longitudinal split tear and improve the accuracy of sonography.
Anatomic variations in the anterior aspect of the shoulder are not uncommon, with a frequency ranging from 2% to 18% depending on the ethnic group.1–7Examples include an accessory head of the biceps brachii muscle, coracobrachialis brevis muscle, accessory subscapularis muscle, and variants of the pectoralis muscles.1 Correct identification of normal variants is important to avoid misdiagnosis of disorders and for accurate diagnosis.1,4,8,9
Sonography has been shown to be an excellent imaging modality to evaluate muscles and tendons, with advantages and disadvantages compared to magnetic resonance imaging (MRI).10,11 Recently the MRI and arthroscopic appearance of the accessory head of the biceps brachii has been described.1,9,12–14 The purpose of this series is to demonstrate the sonographic appearance of the accessory head of the biceps brachii in the bicipital groove. To our knowledge, no prior ultrasound articles describing this anatomic variant have been published. Knowledge of this anatomic variation and its normal appearance on sonography can help prevent false-positive diagnoses of proximal biceps disorders.8,9,15
