A rare case of bilateral sternocleidomastoid muscle variation

Sternocleidomastoid Muscle in Fetuses: Classification, Morphometric Analysis, and Clinical Significance

PURPOSE

This study aimed to examine variations and morphometric properties of the sternocleidomastoid muscle (SCM) in fetuses in terms of infancy and early childhood surgeries.

MATERIALS AND METHODS

Neck regions of 27 fetuses (mean age: 23.30±3.40 wk, sex: 11 boys and 16 girls) fixed with 10% formalin were dissected bilaterally. Photographs of the dissected fetuses were taken in the standard position. Morphometric measurements, such as length, width, and angle, were performed on the photographs using the ImageJ software. In addition, the origin and insertion of SCM were detected. Taking into account the studies in the literature, a classification consisting of 10 types associated with the origin of SCM was carried out.

RESULTS

No statistically significant difference was observed in the parameters in terms of side and sex (P>0.05), except from the linear distance between the clavicle and motor point where the accessory nerve enters SCM (20.10±3.76 for male, 17.53±4.05 for female, P=0.022). Two-headed SCM (Type 1) was detected in 42 out of 54 sides. Two-headed clavicular head (Type 2a) was detected on 9 sides, and 3-headed (Type 2b) on 1 side. A 2-headed sternal head (Type 3) was detected on 1 side. A single-headed SCM (Type 5) was also detected on 1 side.

CONCLUSION

Knowledge related to variations of the origin and insertion of fetal SCM may be helpful in preventing complications during treatments of pathologies such as congenital muscular torticollis in early period of life. Moreover, the calculated formulas may be useful to estimate the size of SCM in newborns.

Bilateral supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver

Many anatomical variants on the sternocleidomastoid muscle have been reported. In this study, supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver were bilaterally displayed. The observed supernumerary heads were classified as follows: one sterno-mastoid, one cleido-occipital and one cleido-mastoid on the right side, and one sterno-mastoid-occipital, four cleido-occipitals, and one cleido-mastoid on the left side. The sterno-mastoid and sterno-mastoid-occipital and the cleido-occipital made the superficial layer of the sternocleidomastoid muscle, while others made deep layer. We discussed clinical relevance and developmental basis of these muscular variations important for clinicians and anatomists.

Bilateral sternocleidomastoid variant with six distinct insertions along the superior nuchal line

Anatomical variations of the sternocleidomastoid muscle (SCM) have been observed to occupy multiple origins and insertion points and have supernumerary heads, sometimes varying in thickness. During routine dissection, a SCM was observed to have six distinct insertions that interface with the course of the superior nuchal line, ending at the midline, bilaterally. This variation was also seen to receive innervation from the accessory nerve as well as the great auricular nerve. To our knowledge, this variant of supernumerary insertions and nerve innervations has not yet been reported. These variants may pose as problematic during surgical approaches to the upper neck and occiput, and should thus be appreciated by the clinician. Herein we discuss the case report, possible embryological origins, and the clinical significance of the observed variant SCM.

Accessory Clavicular Sternocleidomastoid Causing Torticollis in an Adult

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.

Morphological study of the attachment of sternocleidomastoid muscle

INTRODUCTION

The sternocleidomastoid (SCM) muscle is a major muscle of the neck. Classically, this muscle is attached below the sternum and clavicle, although the mode of attachment might vary. As the SCM is related to numerous important neurovascular structures, its variable anatomy is clinically relevant, particularly for neck surgeries. A cadaveric study was performed to establish the variations present in the mode of attachment of the SCM muscle in an Indian population.

METHODS

We studied the variations in the attachment of the SCM muscle during the dissection of 18 cadavers for undergraduate teaching in two medical colleges in West Bengal, India.

RESULTS

Variations in the attachment of the SCM muscle were found in 5 (27.8%) specimens. Of these five specimens, three had unilateral variations and two had bilateral variations. In each specimen, the modes of presentation of the SCM and its fusion with the major bulk were also different.

CONCLUSION

In this study, we found variations in the attachment of the SCM muscle in more than a quarter of the specimens dissected. Surgeons should bear in mind such variations when performing neck surgeries.

Bipartite clavicular attachment of the sternocleidomastoid muscle: a case report

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.