Sternocleiodomastoid Muscle with Five Fleshy Bellies and Thirteen Heads of Origin

Nayak SB

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OJHAS Vol. 15, Issue 3: (July-September 2016)

Case Report
Sternocleiodomastoid Muscle with Five Fleshy Bellies and Thirteen Heads of Origin

Authors
Sudarshan Surendran, Satheesha B Nayak, Deepthinath Reghunathan, Venu Madhav Nelluri
Melaka Manipal Medical College (Manipal Campus), Manipal Academy of Higher Education/Manipal University, Madhav Nagar, Manipal - 576104, Karnataka State, India.

Address for Correspondence
Dr. Satheesha Nayak B,
Professor of Anatomy,
Melaka Manipal Medical College (Manipal Campus),
Manipal Academy of Higher Education/Manipal University,
Madhav Nagar, Manipal-576104,
Karnataka State, India.
E-mail: nayaksathish@gmail.com

Citation
Surendran S, Nayak SB, Reghunathan D, Nelluri VM. Sternocleiodomastoid Muscle with Five Fleshy Bellies and Thirteen Heads of Origin. Online J Health Allied Scs. 2016;15(3):11. Available at URL: http://www.ojhas.org/issue59/2016-3-11.html

Open Access Archives
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Submitted: Aug 3, 2016; Accepted: Oct 6, 2016; Published: Oct 25, 2016

This work is licensed under a Creative Commons Attribution-No Derivative Works 2.5 India License

This Article

Abstract: Sternocleidomastoid (SCM) is the main landmark muscle of the neck. Knowledge of variations of this muscle is very important for radiologist, surgeons, chiropractitioners, plastic surgeons and clinicians in general. We report a unique unilateral variation of SCM observed in an adult male cadaver. The clavicular head of right SCM had four fleshy bellies (B1, B2, B3 and B4). The most medial belly (B1) had three tendons of origin; the next belly just lateral to it (B2) had three tendons of origin; third belly (B4) had four tendons of origin and the lateral most belly (B4) had two tendons of origin. Thus, including the tendon of sternal head, in total, the right SCM had thirteen heads of origin. To the best of our knowledge, this is the first report on a thirteen headed sternocleidomastoid muscle. We review the literature and discuss the clinical importance of the variation in this report.
Key Words: Sternocleidomastoid, variation, radiology, neck surgery, central venous catheterization.

Introduction:

Sternocleidomastoid is one of the functionally and clinically important muscles of the neck. It is a landmark for many clinical, surgical and radiological procedures. It is related to the major nerves and vessels of the neck and involved in dividing the neck into anterior and posterior triangles. Usually, it has a sternal and a clavicular head. Sternal head arises from the anterior surface of the manubrium sterni and the clavicular head takes origin from the superior aspect of the medial part of the clavicle. The two heads unite as they ascend up; the clavicular fibres forming the deeper and the sternal fibres forming the superficial strata. The muscle gets inserted to the posterior part of the lateral surface of the mastoid process and the lateral part of the superior nuchal line.(1) Variations of the sternocleidomastoid muscles are rare. In extremely rare cases, SCM may be congenitally absent.(2,3) A few variations in its origin have been reported earlier. Its insertion seldom shows any variation. Reported variations on its attachment include unilateral or bilateral duplication of sternal or clavicular heads.(4-8) A case of six headed SMC has also been reported.(9) We report here a unique case of SCM with five fleshy bellies and thirteen heads of origin. This is the first report as far as the number of heads of origin or SCM is concerned. We discuss its clinical importance of this variation in our report.

Case Report

During our routine dissection classes for the first year Medical students at Melaka Manipal Medical College (Manipal Campus), in a male cadaver, approximately aged 60 years, we found multiple origins in the sternocleidomastoid muscle (SCM) (figure.01). This variation was unilateral and was found on the right side of the neck. The sternal head of the muscle had a single tendon of origin from the anterior surface of the manubrium sterni and continued up as a single fleshy belly. However, the clavicular head was split into four fleshy bellies as shown in figure 02. Because of the presence of four bellies, the origin of clavicular head extended laterally until the midpoint of the clavicle. The unique feature observed in this case was that the four fleshy bellies of clavicular head of SCM took their origin from clavicle through twelve clearly identifiable tendons (T1-T12 in figure 2). The most medial belly of clavicular head (B1) had three tendons; the second belly (B2) had three tendons; third belly (B3) had four tendons and fourth (lateral most) belly (B4) had two tendons of origin. The four fleshy bellies of sternal head remained separate until they merged with the sternal head of the muscle. While merging with the sternal head, B1 being the shortest belly, was the first to merge with sternal head and the B4 being the longest belly, was the last to merge with the sternal head. There were no variations in the insertion and innervation of the muscle. We believe that this is the first report on a thirteen headed sternocleidomastoid muscle with five fleshy bellies.

Figure 1 (Left): Picture showing the sternocleidomastoid muscle with multiple heads of origin from the clavicle. (SCM - Sternocleidomastoid, T - Trapezius, C - Clavicle, PM - Pectoralis major, P - Platysma with superficial fascia, Arrowheads showing the multiple tendinous heads of sternocleidomastoid)

Figure 2 (Top): Closer look at the multiple heads of origin of sternocleidomastoid muscle (SCM). Note four fleshy bellies (B1-B4) of clavicular head with twelve tendons of origin (T1-T12). The sternal head (SH) with a single tendon and a single fleshy belly can also be seen.

Discussion:

Most of the variations of SCM such as congenital absence, variable number of bellies and continuity with trapezius are attributed to its development. The trapezius and SCM develop from the same myotome of the occipital region. This myotome separates into the ventral SCM and dorsal trapezius muscles. If the myotome fails to separate into two parts, there may be fusion between these two muscles, leading to absence of the posterior triangle of the neck. Improper separation may lead to formation of supernumerary bellies.(10,11) In the current case, the myotome would have divided a few times incompletely in the lower part of the neck, resulting in multiple heads of origin of the muscle. Functionally, SCM is very important in stabilizing the neck, moving the head and neck and also in protecting the main neurovascular bundle of the neck. A precise knowledge of its variations is required to a clinician to achieve success in various clinical procedures. Internal jugular vein lies undercover of SCM and is widely used for central venous catheterizations. The cannula is passed through the lesser supraclavicular fossa, which lies between the sternal and clavicular heads of SCM muscle. Additional heads of origin of this muscle may result in difficulties or errors in the catheterization procedure.(12) Patients with irradiation induced spasm of SCM and conditions such as anterocollis are treated with injection with botulinum toxin. The SCM with additional bellies may require a larger dosage of the toxin in order to relieve the spasm.(13,14) Patients with forward head posture require SCM activation. Accessory bellies such as the ones being reported here might hinder the neck kinematics.(15)

Knowledge of normal and variants of SCM is useful to Chiropractitioners also. Presence of supernumerary bellies may pose problems in specific stretches, trigger point therapy, pillow positioning and exercises.(16,17)

Knowledge of normal anatomy and variations of SCM is also important to plastic surgeons. SCM myocutaneous flaps are being used to correct facial and oral cavity defects.(18) SCM flaps are also used in many other head and neck surgeries such as reconstruction of head and neck defects (19), in lowering the incidence of Frey's syndrome after parotidectomy (20), in reconstruction of temporomandibular joint (21), in reconstruction of laryngo-tracheal defects after tumor resection.(22)

Novelty and clinical importance of the current case:

To the best of our knowledge, this is the first report on a SCM with five fleshy bellies and thirteen tendinous origins. We believe that the embryonic reason for this variation is incomplete multiple splitting of the myotome in the lower part of the neck. This variation might be a curse to the individual aesthetically. However it would prove to be a boon if the individual requires any SCM myocutaneous flaps when he undergoes any reconstructive surgery. Plastic surgeons are largely discouraged from using both sternal and clavicular heads for reconstructive surgery since it leads to a 'flat neck decormity'(23) The additional part of the muscle (B3 and B4 in the current case) can be used without causing functional disturbances and at the same time giving better aesthetic appearance to the neck of the patient. The additional heads of origin and fleshy bellies naturally cover the supraclavicular part of the brachial plexus. Hence they may cause problems during administration of brachial plexus anesthesia. In the current case the greater and lesser supraclavicular fossae are not very obvious because of the multiple origins of SCM. This might cause problems in central venous cannulations and venous pressure recordings. The movements of the neck may not be very symmetrical when the variation is unilateral because the direction of the pull of head by the most lateral part of the variant SCM is not the same as the normal muscle of the opposite side. The lateral most clavicular head might alter the chances of fracture of the clavicle since it is attached almost at the middle of the clavicle and might heal the fractures if any, faster due to the increased blood supply from the muscular vessels to the fracture. The two lateral most additional bellies in the current case may confuse the radiologist and they may be mistaken for posterior triangle tumors. Hence a sound knowledge of this variation is important for various specialties in the medical field.

Conclusion:

The current case of SCM with five fleshy bellies and thirteen tendons of origin is unique and being reported first time in the literature. Some of the additional tendons can be used for tendon grafts without altering the functioning of the muscle. The additional heads may cause problems in anesthesia, central venous cannulation procedures and can cause diagnostic dilemmas to the radiologists. The additional bellies may cause aesthetic and functional disadvantage but at the same time, could be very useful for plastic surgeons in raising SCM myocutaneous flaps.

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