1Department of Surgery, BP Koirala institute of health sciences, Dharan, Nepal
2Department of anatomy, All India Institute of Medical Sciences, India
3Department of Pathology, All India Institute of Medical Sciences, India
4Army Dental Corpse
5Department of surgery, AIIMS, New Delhi
Submission: July 17, 2017; Published: July 31, 2017
*Corresponding author: Anurag Srivastava, Professor and Head, Department of Surgery, AII India Institute of Medical Sciences, New Delhi-110029, India, Tel: 9868397729; Email: firstname.lastname@example.org
How to cite this article: Khadka S, Bhardwaj H, Jain A, Srivastava A, Srivastava A. Sternocleidomastoid Region: The “No Man’s Land” in Neck. Anatomy Physiol Biochem Int J. 2017; 3(2): 555607. DOI:10.19080/APBIJ.2017.03.555607
Anatomically, the neck is conventionally divided into two triangles by the sternocleidomastoid muscle. Its anterior border forms the posterior border of anterior triangle while its posterior border forms the anterior border of posterior triangle. The “sternocleidomastoid region” of the neck however, does not fall in any of the two triangles and thus becomes the “No Man’s Land” of the neck. There is a lack of defined surgical anatomy of the sternocleidomastoid region in literature, which harbors a number of vital structures and thus would fall under none of the triangles. To a student of anatomy this creates confusion. To resolve this conflict, in present article we identify this region as a distinct zone THE “Sternocleidomastoid region”.
Keywords: Anatomy of Neck; Anterior Triangle; Posterior Triangle; Sternocleidomastoid region; Head & Neck Surgery
Sternocleidomastoid muscle is an important structure of the neck. This rhomboid shaped muscle lies obliquely in the neck, extending from manubrium sterni, and medial third of the clavicle antero-inferiorly to the mastoid process and occipital bone postero-superiorly. The muscle superficially crosses various vital structures in the neck such as trachea, oesophagus, common carotid artery, internal jugular vein, vagus nerve, symphathetic chain and jugular group of lymph nodes. It is supplied by the occipital and superior thyroid arteries and receives its nerve supply from 11th cranial (Spinal root of accessory) and 2nd & 3rd cervical (Proprioceptive and motor) nerves. Sternocleidomastoid muscle separates the two triangles in each half of the neck  (Figure 1). The Anterior Triangle is described as being bounded by mid line anteriorly, anterior border of sternocleidomastoid posteriorly and the lower border of mandible superiorly. The Posterior triangle is described as bounded by posterior border of sternocleidomastoid, anterior border of trapezius and middle third of clavicle inferiorly.
Superficial relations of Sternocleidomastoid: Skin, External jugular vein, Great auricular nerve, Transverse cervical nerve,
Platysma, Superficial lamina of deep cervical fascia, tail of parotid gland.
Deep relations of Sternomastoid muscle (Figure 2a-2c):
The point at the junction of the upper and middle third of
the posterior border of sternocleidomastoid where four
cutaneous nerves and spinal accessory nerve emerge is
termed “nerve point of the neck”. In ‘cervical plexus nerve
block’ the anesthetic agent is injected at this site [2,3].
Trauma surgeons divide neck region into zone 1, zone 2
and zone 3. Anatomic contents of different zones of neck  are
shown in Figure 3
I. Zone I: Sternal notch of clavicle to cricoid cartilage
Contents: Major vasculature of superior mediastinum,Subclavian artery and vein, common carotid artery, vertebral
artery, internal jugular vein, trachea, lung apex, esophagus,
thyroid, vagus nerve, recurrent laryngeal nerve, phrenic
nerve, cervical spine.
II. Zone II: Cricoid cartilage to angle of mandible
Sternocleidomastoid is a long muscle which acts as an
important landmark in the neck as it divides the neck into
anterior and posterior triangles. The Anterior Triangle is
described as being bounded by mid line anteriorly, anterior
border of sternocleidomastoid posteriorly and the lower border
of mandible superiorly. The Posterior triangle is described as
bounded by posterior border of sternocleidomastoid, anterior
border of trapezius and middle third of clavicle inferiorly.
Inferiorly, the muscle has two heads, tendinous sternal head
attached to manubrium sterni and muscular clavicular head
attached to medial third of the clavicle (clavicular head).
Superiorly, muscle is attached to the mastoid process of
the temporal bone and superior nuchal line of the occipital
bone. The sternal head ascends across the medial part of the
sternoclavicular joint, and widens as it overlaps the clavicular
head a short distance above the clavicle, fusing with it about
half way up the neck. In the postero-superior part its anterior
border becomes thick before it inserts into the anterior surface
of the mastoid process while the posterior border becomes thin
and aponeurotic before attaching to the lateral surface of the
mastoid process and lateral half of the superior nuchal line .
The width of the muscle could be up to 4-5 cm in muscular
men. It is supplied by three sternocleidomastoid arteries. Out
of which upper two arise from the occipital artery and the
lower one arises from the superior thyroid artery. The carotid
sheath with its contents is overlapped by sternocleidomastoid
muscle in most of its extent, however in literature it is described
as a content of anterior triangle. This indistinct demarcation
thus causes dilemma in understanding the applied anatomy
of this region. The clinician, the radiologist and surgeons
have to be cognizant of the vital structures located deep to
sternocleidomastoid muscle. Surgical excision of any swelling
along its length such as branchial cyst or enlarged lymph nodes
needs precise understanding of this region as the structures
injured and surgical approach varies in different zones. Trauma
surgeons divide the neck into three zones (zone 1, zone 2 and
zone 3) extending from skull base to the sternal notch based
on the urgency of exploration. The triangle based description
of neck anatomy is not inclusive of this important region of
the neck, “The sternocleidomastoid region”. This review thus
highlights the deficiency in teaching of head and neck anatomy.