Bipartite clavicular attachment of the sternocleidomastoid muscle: a case report

Abstract

Morphological variations of the sternocleidomastoid (SCM) muscle assume relevance during attempted surgical interventions in the cervical region. The present study reports bipartite clavicular attachment of the SCM in the neck of an adult male cadaver during performance of a routine anatomy demonstration. The anomaly was unilaterally observed on the left side of the neck. The clavicular head of the muscle exhibited two bellies, one medial and one lateral. While the medial belly was fused with the sternal head, the lateral belly appeared to blend with the medial. Cranially, the SCM attached to the mastoid process and superior nuchal line. We have attempted to elucidate the embryological basis of the above muscular variant. Additionally, we discuss its clinical relevance, highlighting the utility of the SCM in various reconstructive procedures. We assert that detailed anatomical knowledge of such SCM variants is of utility not only to the gross anatomist, but also for neck and orthopaedic surgeons and anaesthetists. Moreover, radiologists require familiarity with such aberrations to decipher magnetic resonance imaging scans of the cervical region.

Accessory Clavicular Sternocleidomastoid Causing Torticollis in an Adult

“…In humans, there are several known variations of the sternocleidomastoid muscle, e.g., it can have different layers, superficial and deep, and can have many insertions/branches. [1][2][3][4] Most of the documented variations are located in the origin, with different numbers of insertions/branches and locations in the sternal and clavicular areas. In our case, the anomaly was an additional belly from the mid-clavicle fusing with the normal sternoclavicular portion in the middle, forming an inverted Y-shaped muscle.…”

“…[6][7][8] Most of the documented cases of anomalous sternocleidomastoid have been reported in anatomy and morphology journals from authors working in medical colleges and involved in dissection of cadavers for teaching purposes. 4,[8][9][10][11] These variations can have practical significance in patients undergoing various procedures in the head and neck regions, where the sternocleidomastoid muscle is used as an important anatomical landmark. Any variation may lead to problems in reaching the desired anatomical region in certain blind procedures.…”

“…Sahibzada Nasir Mansoor, MBBS, FCPS, MCPS (HPE), MSc a and Farooq Azam Rathore, MBBS, FCPS, MSc b physicians and surgeons working in this complex area if they are unaware of the possible variations. 4) Congenital muscular torticollis is a rare pathology seen mostly in neonates. The main cause is shortening and fibrosis of the sternocleidomastoid muscle (also known as fibromatosis colli).…”

Bilateral Variation in the Origin of Sternocleidomastoid Muscle

“…Previously a case of third head of SCM which was unilateral has been reported. [2,3] Some other authors have also reported cases with multiple slips. [4,5] The bilateral variation of additional head in the sternal origin and additional head in the clavicular origin of sternocleidomastoid have been also reported.…”

Variation of Bilateral Multiheaded Sternocleidomastoid Muscle

“…The muscle descends obliquely across the side of the neck and divides it into anterior and posterior triangles (1)(2)(3).…”