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Key Words: accessory; adult; anomaly; sternocleidomastoid; torticollis

INTRODUCTION

The sternocleidomastoid is a major muscle of the neck with an important anatomical location. It divides the neck into an anterior and posterior triangle. The muscle arises from the sternum and the clavicle and inserts into the mastoid process. It is supplied by the spinal root of the accessory nerve. The main action of the sternocleidomastoid is rotation of the head to the opposite side along with flexion of the neck. It also acts as an accessory muscle of inspiration. The depression between the sternal and clavicular head is called the lesser suprascapular fossa.1) The greater suprascapular fossa lies

behind the sternocleidomastoid and in front of the anterior border of the trapezius. The sternocleidomastoid is of major interest to physicians and surgeons working in the neck area because it is an important landmark for locating structures such as the carotid artery, jugular veins, nerves, and plex-uses. Such anatomical insight is essential for procedures including central line placement, anesthetic procedures, and nerve and ganglion blocks.2) The muscle can also be used as a myocutaneous flap for facial defects and oral cavity defects.3) Anatomical variations of the sternocleidomastoid have been documented mostly in cadavers. Any similar anatomical variation in a patient could cause problems for

Received: August 17, 2017, Accepted: March 20, 2018, Published online: April 7, 2018a Department of Rehabilitation Medicine, Combined Military Hospital, Pano Aqil Cantonment, Sind, Pakistan b Department of Rehabilitation Medicine, PNS Shifa Hospital, Karachi, PakistanCorrespondence: Sahibzada Nasir Mansoor, MBBS, FCPS, MCPS (HPE), MSc, Department of Rehabilitation Medicine, Combined Military Hospital, PanoAqil Cantonment, Pano Aqil, Sukkur, Sindh, Pakistan, Email:drnasirmansoor@gmail.comCopyright © 2018 The Japanese Association of Rehabilitation Medicine

Progress in Rehabilitation Medicine 2018; Vol. 3, 20180006doi: 10.2490/prm.20180006

Background: Sternocleidomastoid anomalies are mostly discovered in cadavers during routine dissection. Such anomalies causing torticollis are rare in adults. We report a case of accessory mid-clavicular head of the sternocleidomastoid causing torticollis in an adult. Case: A previously healthy 27-year-old man presented with neck and shoulder pain following heavy manual work. On examination, he had mild restriction of left tilt of the head and right rotation of the neck. Palpation revealed a bipartite right sternocleidomastoid. There was no abnormal posturing of other body parts. The range of motion of the cervical spine was limited to rotation of 70° and tilt of 38° on the left side and rotation of 65°and tilt of 46° on the right side. Neck extension was 40°. The accessory sternocleidomastoid muscle belly was visible and inserted at the middle of the clavicle. Musculoskeletal ultrasound imaging confirmed the diagnosis. Radiological images of the cervical spine and electromyography were normal. Myectomy of the lateral accessory clavicular belly of the sternocleidomastoid was planned, but the patient declined this treatment. Currently, he uses oral analgesics and participates in occasional sessions of physical therapy. Discussion: An accessory sternocleidomastoid can result in torticollis because it causes a physical restriction preventing the neck from tilting and rotating to the opposite side. In mild cases, the anomaly may remain undiagnosed until adulthood and can be confused with cervical dystonia and fibromatosis colli. Knowledge of the anatomy and possible variants of the sternocleidomastoid muscle is of the utmost importance to medical practitioners involved in the diagnosis and management of problems in the neck area. Variants of the sternocleidomastoid can be a concern for surgeons, physicians, and anesthetists performing interventional procedures on the neck because of possible confusion of anatomical landmarks.

CASE REPORTAccessory Clavicular Sternocleidomastoid Causing

Torticollis in an AdultSahibzada Nasir Mansoor, MBBS, FCPS, MCPS (HPE), MSc a and Farooq Azam Rathore, MBBS, FCPS, MSc b

Copyright © 2018 The Japanese Association of Rehabilitation Medicine

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 fibromato-sis colli).5) Torticollis in adults resulting from variation in sternocleidomastoid origin is extremely rare, and this fact can lead to a missed diagnosis. Unilateral anomalies of the sternocleidomastoid and the resulting subtle effects may de-lay the diagnosis until adulthood. Timely management of the condition can lead to significant improvement of symptoms.

Here, we report a case of torticollis caused by an accessory clavicular head of the sternocleidomastoid in a young adult male. Informed consent to publish this report was obtained from the patient.

CASE DESCRIPTION

A previously healthy 27-year-old man presented with a fixed, mild right tilt of the head and left rotation of the neck since childhood. His birth history was not available. He was an infantry soldier by occupation. The abnormality was mild and was ignored by the patient because it was asymptomatic. Healthcare professionals also were unaware of the condi-tion due to its subtlety. The patient presented with pain in the neck and shoulder after doing heavy manual work that required continued posturing. He also complained of chronic cervicogenic headaches and chronic dull-aching, nonradiat-ing, mild to moderate intensity pain of the upper posterior thorax. On inspection, a bipartite right sternocleidomastoid, dividing above midway, was identified. The lateral belly of the muscle was inserted at the middle of the clavicle, whereas the medial belly fused at the sternal and medial clavicular insertion point (Fig. 1). Palpation of the neck musculature revealed a nontender sternocleidomastoid muscle dividing in the middle into two bellies, and one accessory clavicular head arising from the middle of the clavicle (Fig. 2). There was no abnormal posturing of other body parts. The patient had a limited cervical range of motion (ROM). Neck rotation was 70° with a 38° tilt on the left side, and neck extension was 40°. Right rotation was 65°, with a tilt of 46°.

Musculoskeletal ultrasound examination confirmed the diagnosis of accessory clavicular head of the sternocleido-mastoid. X-ray images of the cervical spine and electromy-ography were normal.

On a trial basis, the patient was prescribed diclofenac sodium 50 mg three times a day and tizanidine 2 mg twice a day. Physical therapy (PT) was also prescribed and included

three times a week application of ultrasound therapy of the affected muscles, followed by stretching and strengthening exercises of the neck. However, although regular PT sessions lasted for 3 weeks, the ROM did not improve. Interestingly, the pain reduced from a visual analogue scale of 6/10 to 3/10.

A surgical referral was made because conservative treat-ment did not improve ROM. The surgeon advised the patient to undergo a myectomy of the lateral accessory bipartite clavicular belly of the right sternocleidomastoid; however, the patient refused any form of surgical treatment.

At present, the patient occasionally takes oral analgesics with occasional massage and sessions of physical therapy for pain relief.

Informed consent was obtained from the patient.

2 Mansoor, S and Rathore, F: Accessory Sternocleidomastoid causing torticollis in adults

Fig. 1. Accessory clavicular head of the sternocleidomastoid inserted at mid-clavicle. Normal sternoclavicular attachment is visible on the right side (lateral view).

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DISCUSSION

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/branch-es.1–4) 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 fus-ing with the normal sternoclavicular portion in the middle, forming an inverted Y-shaped muscle.

Less commonly, such abnormalities are reported in the in-sertion area of the mastoid and the superior nuchal line. The anomalous muscle can have sternomastoid, sterno-occipital, or cleido-occipital parts and insertions/branches.6) There can be separate sternomastoid and cleidomastoid portions of the muscle, or fusion with the trapezius.7) The findings can be unilateral or bilateral.

Variations in the sternocleidomastoid muscle origin and insertion have been documented in the literature.6–8) 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.4,8–11) These

variations can have practical significance in patients un-dergoing various procedures in the head and neck regions, where the sternocleidomastoid muscle is used as an impor-tant anatomical landmark. Any variation may lead to prob-lems in reaching the desired anatomical region in certain blind procedures. Therefore, the physicians, surgeons, and anesthetists involved in interventional procedures in the neck area need to know the possible variations in the sterno-cleidomastoid origin and insertion.

In this case report, another dimension of sternocleidomas-toid muscle variation has been highlighted. An accessory clavicular head of the sternocleidomastoid muscle led to mild torticollis, restriction in neck movements, and pain on prolonged posturing. The patient had a limited range of neck rotation to the opposite side, along with limited extension, as a result of the physical limitation effect of the accessory clavicular head. The current case is also unusual because the patient was not diagnosed until he reached adulthood. He was 27 years old at presentation and was examined for neck and shoulder pain. It was only at this point that the anomaly was detected.

Congenital muscular torticollis (CMT) was an important differential diagnosis in this case. CMT is unilateral mus-cular shortening or contracture of the sternocleidomastoid

Prog. Rehabil. Med. 2018; Vol.3, 20180006 3

Fig. 2. A right accessory clavicular sternocleidomastoid inserting at mid-clavicle and normal sternoclavicular attachments of both sternocleidomastoids were vis-ible on the anterior view.

Copyright © 2018 The Japanese Association of Rehabilitation Medicine

caused by muscle atrophy and fibrosis, leading to persistent neck posturing and tilt.9,12) It usually resolves by the age of 8 months and rarely progresses into adulthood. This condition has been reported in the literature in adults with mild torti-collis, misdiagnosis, and cervical dystonias.5,9) We differen-tiated CMT by the clinical history, the age at presentation, physical examination, and by musculoskeletal ultrasound examination of the sternocleidomastoid muscle. Cervical dystonia was also ruled out because of the absence of spasm, tremor, or sensory deficits. Findings of electrodiagnostic studies of the sternocleidomastoid were also unremarkable.

In the current case, the accessory clavicular origin of the sternocleidomastoid muscle could have resulted from abnor-mal splitting in the mesoderm of the post-sixth brachial arch. However, this additional clavicular head of the sternocleido-mastoid muscle could be of use to plastic surgeons planning to use it as a muscle graft elsewhere.10)

Anomalies of the sternocleidomastoid muscle are liable to be misdiagnosed as muscular spasm, cervical dystonia, or fibromatosis colli,12) and such misdiagnosis can lead to pro-longed morbidity for the patient. A high index of suspicion and clinical acumen needs to be developed to diagnose such rare cases of torticollis.

The presence of an accessory head of the sternocleidomas-toid can cause torticollis. In some cases, this condition can remain undiagnosed until adulthood. It can also be confused with cervical dystonia and fibromatosis colli. Such anomalies can be a concern for surgeons, physicians, and anesthetists performing interventional procedures in the neck area be-cause of confusion of local anatomical landmarks. Knowl-edge of sternocleidomastoid morphology and anomalies is of the utmost importance to doctors involved in the diagnosis and management of problems in the neck area.

ACKNOWLEDGEMENT

The authors duly acknowledge Miss Fiona JVW Stephen-son, FRCN, RN, for her invaluable time in improving the English grammar and syntax of the manuscript.

CONFLICTS OF INTEREST

The authors declare that there are no conflicts of interest.

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4 Mansoor, S and Rathore, F: Accessory Sternocleidomastoid causing torticollis in adults