Bilateral four heads of the sternocleidomastoid muscle

Architecture of head and neck soft tissues and associated entheses: An exploration of sexual dimorphism in, and population differences between, New Zealand and Thai individuals

Understanding the musculoskeletal anatomy of soft tissues of the head and neck is important for surgical applications, biomechanical modelling and management of injuries, such as whiplash. Additionally, analysing sex and population differences in cervical anatomy can inform how biological sex and population variation may impact these anatomical applications. Although some muscles of the head and neck are well-studied, there is limited architectural information that also analyses sex and population variation, for many small cervical soft tissues (muscles and ligaments) and associated entheses (soft tissue attachment sites). Therefore, the aim of this study was to present architectural data (e.g., proximal and distal attachment sites, muscle physiological cross-sectional area, ligament mass, enthesis area) and analyse sex and population differences in soft tissues and entheses associated with sexually dimorphic landmarks on the cranium (nuchal crest and mastoid process) and clavicle (rhomboid fossa). Through the dissection and three-dimensional analysis of 20 donated cadavers from New Zealand (five males, five females; mean age 83 ± 8 years; range 67-93 years) and Thailand (five males, five females; 69 ± 13 years; range 44-87 years), the following soft tissues and their associated entheses were analysed: upper trapezius, semispinalis capitis and the nuchal ligament (nuchal crest); sternocleidomastoid, splenius capitis and longissimus capitis (mastoid process); the clavicular head of pectoralis major, subclavius, sternohyoid and the costoclavicular (rhomboid) ligament (rhomboid fossa). Findings indicate that although muscle, ligament and enthesis sizes were generally similar to previously published data, muscle size was smaller for six of the eight muscles in this study, with only the upper trapezius and subclavius demonstrating similar values to previous studies. Proximal and distal attachment sites were largely consistent with the current research. However, some individuals (six of 20) had proximal upper trapezius attachments on the cranium, with most attaching solely to the nuchal ligament, contrasting with existing literature, which often describes attachment to the occipital bone. With respect to sexual dimorphism, the Thai sample exhibited more sex differences in muscle size than the New Zealand sample, but for enthesis size (area), both samples had the same amount of statistically significant sex differences (5 of 10). Additionally, some significant population differences were found when comparing muscle and enthesis size data between the New Zealand and Thai samples. Despite these findings, no sex or population differences were found for ligament size (mass) in either group. This paper presents new architectural data for several understudied areas of the head and neck, as well as providing analyses on sex and population differences, two areas that have limited representation in anatomy.

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.

Variation of the sternocleidomastoid muscle: a case report of three heads and an accessory head

PURPOSE

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.

METHODS

An 85-year-old Korean male cadaver was dissected and a SMC with unilateral supernumerary heads was identified.

RESULTS

Three heads and an accessory belly of the sternal head were recorded on the left side. There were two clavicular heads, one lateral and one medial. The sternal head originated inferior to the manubrium of the sternum. A small belly arose from the sternal head and merged to the lateral clavicular head on the C5 vertebrae level. These bellies inserted into the mastoid process of the temporal bone.

CONCLUSIONS

These variants may be problematic during surgical approaches to the upper neck and occipital, and should thus be appreciated by the clinician.

Effective botulinum toxin injection guide for treatment of cervical dystonia

The aim of this study was to elucidate the distribution of the accessory nerve within the sternocleidomastoid muscle (SCM) to aid identifying the optimum sites for botulinum neurotoxin (BoNT) injections and applying chemical neurolysis. Thirty SCM specimens from 15 Korean cadavers were used in this study. Sihler's staining was applied to 10 of the SCM specimens. Transverse lines were drawn in 20 sections to divide the SCM into 10 divisions vertically, and a vertical line was drawn into the medial and lateral halves from the mastoid process to the sternoclavicular joint. The most densely innervated areas were 5/10-6/10 and 6/10-7/10 along the lateral and medial parts of the muscle, respectively. We suggest injecting BoNT in the medial region 6/10-7/10 along the SCM prior to injecting in the lateral region 5/10-6/10 along the muscle to ensure safe and effective treatment. Clin. Anat. 33:192-198, 2020. © 2019 Wiley Periodicals, Inc.

Ipsilateral Hypertrophy of the Mastoid Process in Surgical Cases of Congenital Muscular Torticollis

OBJECTIVE

This study was to investigate ipsilateral hypertrophy of the mastoid process in the patients with congenital muscular torticollis (CMT).

DESIGN

Retrospective cross-sectional study.

PATIENTS

Children with CMT.

METHODS

A total of 212 surgical cases of patients with CMT (age: 50.9 ± 44.3 months) and 212 age- and gender-matched controls (age: 50.4 ± 44.2 months) were included. The mastoid process volume was calculated and compared for both groups on the computed tomography axial images. A linear regression analysis was performed between the age and the intrasubject volume difference in the mastoid process.

RESULTS

The volume of the mastoid process in the CMT side was significantly larger than that of the non-CMT side in the CMT group (32.2 ± 30.3 cm³ vs 21.9 ± 22.8 cm³; P < .001). In the control group, there was no significant difference between the volume of the right and left mastoid process (21.6 ± 24.6 cm³ vs 21.2 ± 23.8 cm³; P = .472). The intrasubject volume difference in the mastoid process in the CMT group showed a linear increase with the age (adjusted R ² = 0.286; P < .001), and the volumetric asymmetry of the mastoid process became more severe over age compared to the control group.

CONCLUSION

We showed ipsilateral hypertrophy of the mastoid process in patients with CMT and demonstrated that the volumetric asymmetry increased with age.

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.

Sonographic Guide for Botulinum Toxin Injections of the Neck Muscles in Cervical Dystonia

Intramuscular botulinum toxin (BoTX) injection is the first-line treatment of cervical dystonia. Poor treatment outcomes and some side effects, however, have been reported after BoTX applications. One of the most important reasons is incorrect localization of the needle during toxin injections. Without imaging, it is impossible to verify precise needle positioning in the proper muscle. Ultrasound has been recommended because of its high capability in illustrating most of the neck muscles. This review article discusses how ultrasound imaging can be used to scan/access neck muscles, mainly from the perspective of BoTX injections.