''Costodeltoideus'': A Rare Anomaly of the Deltoid Muscle

During routine dissection for medical students at the Department of Anatomy, Usmanu Danfodiyo University, Sokoto, Nigeria, an adult male cadaver was found with an unusual, unilateral, long cylindrical muscle mass, within a separate fascial sheet, at the back of the left shoulder, extending from the axillary border of the scapular to the shaft of the humerus. Among variations of the deltoid muscle, anomalous origin of the deltoid muscle from the lateral (axillary) border of the scapular is exceptionally uncommon. While the prevalence is yet unknown, the knowledge of this unique variation, and its influence on the normal anatomical landmarks of the back of the scapular and shoulder region, are clinically relevant to surgeons who harvest posterior deltoid and scapular flaps for a wide range of posterior scapular and shoulder joint reconstructions. Knowledge of this variation will help to ensure a better understanding and accurate interpretation of radiological images, and serve as a guide to circumvent difficulties during reconstructive shoulder joint procedures.

Key Words: Costodeltoideus, Rare Anomaly, Deltoid, Origin, Scapula, Surgery