Posterior Neck Triangles and Suboccipital Triangle Flashcards
Review trapezius and levator scapulae muscles if you have forgotten!
(a) State the extents of the neck.
(b) Skeleton of the neck consists of:
(a) Superiorly: the base of cranium and the inferior border of mandible
Inferiorly: the level of the thoracic inlet, clavicle and scapula
(b) cervical spine, hyoid bone, laryngeal cartilages, and the base of skull.
(a) Superficial fascia; consists of a thin layer of loose areolar tissue and contains a thin sheet of muscle called platysma. It also contains cutaneous nerves, superficial veins, superficial lymph nodes and lymph vessels.
(b) Deep cervical fascia [fascia colli]; consists of three layers
(i) Investing layer; follow the rule of 2
~ encloses 2 muscles, trapezius and sternocleidomastoid
~ forms roof of 2 triangles; anterior and posterior triangle
~ splits to enclose 2 glands; submandibular and parotid
~ splits to enclose 2 spaces; suprasternal and supraclavicular
~ forms 2 fascial slings (pulleys) for inferior belly of omohyoid and intermediate tendon of digastric
(ii) pretracheal fascia; covers the front and sides of the trachea. It splits to enclose the thyroid gland forming its capsule. It allows free movement of the trachea during swallowing.
(iii) prevertebral fascia; lies in front of the prevertebral muscles. It covers the phrenic nerve and scalene muscles as well.
[Diagram: Fascial Organization of the Neck, transverse section]
[Diagram 2: Fascial Organization of the Neck]
[Diagram 3: Fascial Organization of the Neck]
[Diagram 4: Fascial Organization of the Neck]
[Diagram 5: Fascial Organization of the Neck]
Further notes:
Modifications of the pretracheal layer: The fascia at the back of the thyroid lobe is thickened to form a ligament (ligament of Berry) which gains attachment to the cricoid cartilage. The carotid sheath is said to be formed from fusion of prevertebral fascia and pretracheal fascia.
Osteology of the Hyoid Bone
Click on Answer to view.
Notes:
✓ This is a U-shaped bone that forms part of the laryngeal skeleton. It is suspended from the tips of the styloid processes by stylohyoid muscles and ligaments.
✓ It is derived from 2nd and 3rd pharyngeal arches; lesser horns and upper part of the body arise from the 2nd pharyngeal arch whereas the lower part of the body and the greater horns arise from the third pharyngeal arch.
✓ Its primary role is for muscle attachment, but it also provides structural support for the larynx and pharynx.
✓ It is a delicate bone that has vital medicolegal relevance. It is commonly broken during strangulation. [X-ray image: hyoid fracture]
The platysma muscle is a broad sheet of muscle of varying prominence within the subcutaneous tissue of the neck. State its innervation and the effect of its contractions.
(a) Innervation: cervical branch of facial nerve
(b) Effect of its contractions:
✔ mandibular depression
✔ depresses the lower lip and corners of the mouth in expressions of horror or surprise
✔ it creates tense oblique ridges in the lateral skin
✔ diminished concavity between the lower jaw and lateral neck
Further notes:
~ Acting from above, the platysma produces vertical ridges in the skin of the neck releasing the pressure of skin over the underlying veins and thus helps in the venous return. It, therefore, serves to ease the pressure of tight collar.
~ Though the risorius appears to be a continuation of platysma, it has a different nerve supply, namely, the buccal branch of facial nerve.
State the anatomical landmarks of the posterior neck triangle.
- occiput
- mastoid process
- atlas
- axis
- clavicle
- [Diagram: surface anatomy of the neck]
Describe the attachments, and clinical significance of investing fascia of the neck.
Attachments:
1. Superiorly: External occipital protuberance, superior nuchal line, mastoid process, and lower border of mandible from behind forwards.
2. Inferiorly: spine of scapula, acromion process, upper aspect of clavicle, and jugular notch of manubrium sterni from behind forwards.
3. Anteriorly across the midline, it becomes continuous with its counter part of the other side. In the anterior midline it is attached to symphysis menti, hyoid bone jugular notch from above downwards.
4. Posteriorly: Ligamentum nuchae and spine of 7th cervical vertebra.
5. [Diagram: investing fascia] [Diagram 2]
Clinical significance:
The investing fascia compartmentalizes neck structures, limiting the spread of infection (e.g., preventing a superficial skin abscess from spreading deeper into the neck).
Above the suprasternal notch, the investing fascia of the neck splits into two layers to enclose suprasternal space (of Burns) before being attached to the anterior and posterior borders of the suprasternal notch. State the contents of the suprasternal notch.
(a) sternal heads of sternocleidomastoid muscles,
(b) jugular venous arch,
(c) interclavicular ligament, and
(d) lymph node (sometimes).
[Diagram: Sternum]
[Diagram: Suprasternal space]
[Diagram 1: Contents of the Suprasternal space]
[Diagram 2: Contents of the Suprasternal space]
[Diagram illustrating the splitting of the investing fascia to enclose the suprasternal notch]
Above the middle third of clavicle, the investing fascia splits into two layers to enclose the supraclavicular space. The anterior and posterior layers get attached to the anterior and posterior borders of the upper surface of the clavicle. The posterior layer encloses the inferior belly of omohyoid and after being attached to clavicle it becomes continuous with the posterior layer of clavipectoral fascia. State the contents of the supraclavicular space.
(a) terminal part of the external jugular vein, and
(b) supraclavicular nerves before they become cutaneous.
State the boundaries of the posterior neck triangle.
Anterior border: Posterior border of sternocleidomastoid muscle
Posterior border: Anterior border of trapezius muscle
Inferior border: middle 1/3 of clavicle
Superior border (apex): Meeting point of sternocleidomastoid and trapezius muscles at the superior nuchal line of the occipital bone.
[Diagram]
Note: The sternocleidomastoid muscle runs diagonally across the neck and divides it into anterior and posterior triangles.
State the following regarding the sternocleidomastoid muscle: attachments, actions, blood supply, and nerve supply.
Origin:
Arises by 2 heads: [Diagram]
1. Sternal head: arises by a rounded tendon from the superolateral part of the front of the manubrium sterni
2. Clavicular head, is flat and musculoaponeurotic. It arises from the medial third of the superior surface of the clavicle
Insertion: by (a) a thick tendon on the lateral surface of the mastoid process extending from its tip to its base, and (b) by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.
Arterial Supply:
The sternocleidomastoid is supplied by branches of following arteries:
1. Upper part, by occipital and posterior auricular arteries
2. Middle part, by superior thyroid artery
3. Lower part, by suprascapular artery
Innervation:
~ Spinal accessory nerve.
~ Ventral rami of C3 and C4, which are mostly sensory and carry proprioceptive sensations from the muscle.
Actions:
Unilateral contraction:
1. ipsilateral neck flexion
2. contralateral rotation of the head
Bilateral contraction:
1. flexion of lower and middle cervical spine
2. extension of atlanto-occipital joint
State the relations of the sternocleidomastoid muscle.
[This is best studied with an atlas!]
Superficial Relations
✔ Skin
✔ Platysma
✔ Cutaneous nerves: (a) Great auricular, (b) Transverse cervical, (c) Medial supraclavicular, (d) Lesser occipital
✔ External jugular vein
✔ Superficial cervical lymph nodes
✔ Parotid gland
Deep Relations
In the upper part
(a) Muscle: Posterior belly of digastric, longissimus capitis, and splenius capitis
(b) Artery: Occipital artery
In the middle part
(a) Muscles: Levator scapulae, scalenus anterior, scalenus medius, scalenus posterior, splenius capitis, inferior belly of omohyoid
(b) Arteries: Common carotid, internal carotid
(c) Veins: Internal jugular, anterior jugular
(d) Nerves: Vagus, spinal accessory, cervical plexus, brachial plexus (upper part), ansa cervicalis (inferior root)
(e) Glands: Thyroid gland, lymph nodes
In the lower part
(a) Muscles: Sternohyoid, sternothyroid, scalenus anterior
(b) Arteries: Suprascapular, transverse cervical
(c) Veins: Anterior jugular
(d) Nerves: Brachial plexus (lower part), phrenic nerve
State the clinical relevance of the sternocleidomastoid muscle.
☯︎ Torticollis or wry neck: It is a clinical condition in which head is bent to one side and chin points to the opposite side. This occurs due to spasm of sternocleidomastoid and trapezius muscles supplied by spinal accessory nerve.
– The spasmodic torticollis is characterized by repeated painful contractions of the trapezius and sternocleidomastoid muscles on one side. It is usually caused by exposure to cold and maladjustment of pillow during sleep.
– The reflex torticollis occurs due to irritation of spinal accessory nerve caused by inflamed or suppurating lymph nodes.
– The congenital torticollis occurs due to birth injury to muscle. Permanent torticollis may occur due to subsequent ischemic contracture.
☯︎ Sternomastoid tumor: It is the swelling in the middle third of the sternocleidomastoid muscle due to edema and ischemic necrosis caused by birth trauma.
Outline the structures present in the superficial fascia of the posterior neck triangle.
☑ platysma
☑ 4 cutaneous branches of the cervical nerve plexus: lesser occipital, great auricular, transverse cutaneous nerve of neck, supraclavicular nerves (lateral, intermediate and medial) [Diagram]
☑ external jugular vein [formed behind the angle of the mandible by joining of the posterior division of the retromandibular vein and the posterior auricular vein. It drains into the subclavian vein.]
a) What forms the roof of the posterior neck triangle?
b) What structures pierce the roof of the posterior triangle?
a) It is formed by the investing layer of the deep cervical fascia, stretching between the sternocleidomastoid and trapezius muscles.
b) Structures that pierce its roof:
1. Four cutaneous branches of cervical plexus:
✔ Lesser occipital nerve (C2)
✔ Great auricular nerve (C2, C3)
✔ Transverse cervical nerve (C2, C3)
✔ Supraclavicular nerves (C3, C4).
They pierce the roof near the middle of the posterior border of the sternocleidomastoid muscle.
2. External jugular vein: It begins just below the angle of mandible, runs downwards and backwards crossing the sternocleidomastoid obliquely and under the cover of platysma.
(a) What forms the floor of the posterior neck triangle?
(b) The muscular floor of posterior triangle is covered by prevertebral layer of deep cervical fascia, which forms the ________________ of the floor of the posterior triangle.
(a) The floor of posterior triangle is muscular and is formed from above downwards by the following muscles:
1. Semispinalis capitis
2. Splenius capitis
3. Levator scapulae
4. Scalenus medius
5. First digitation of serratus anterior (sometimes).
[Diagram: Floor of the Posterior Triangle of Neck]
(b) fascial carpet
Further notes:
☑ The fascial carpet forms axillary sheath around subclavian artery and brachial plexus travelling from the root of the neck to the upper limb.
☑ The lower part of the posterior triangle is crossed by inferior belly of omohyoid superficial to the fascial carpet.
Semispinalis capitis
(a) Origin
(b) Insertion
(c) Action
(d) Innervation
(a) Origin: articular processes of vertebrae C4-C7, transverse processes of vertebrae T1-T6
(b) Insertion: Between superior and inferior nuchal lines of occipital bone
(c) Action: Bilateral contraction - extension of head, cervical and thoracic spine Unilateral contraction - lateral flexion of head, cervical and thoracic spine (ipsilateral), rotation of head, cervical and thoracic spine (contralateral)
(d) Innervation: descending branches of greater occipital nerve (C2) and spinal nerve C3
State the clinical correlation regarding the fascial carpet of the posterior triangle of the neck.
Pus collected in the posterior triangle deep to its fascial carpet from tubercular cervical vertebrae [tuberculosis infection] may track downwards and laterally along the axillary sheath to first appear in the axilla or even in the arm subsequently. [The prevertebral fascia extends around the brachial plexus and axillary artery (continuation of subclavian artery) as the axillary sheath.]
The posterior triangle is subdivided into two parts by the inferior belly of the omohyoid, which crosses the lower part of the triangle obliquely upwards and forwards. List those two parts.
(a) a larger upper part called occipital triangle
(b) a small lower part called subclavian (supraclavicular) triangle.
[These parts are so named because they contain occipital and subclavian arteries, respectively.]
[Diagram]
State the contents of the occipital triangle.
(a) Spinal accessory nerve
(b) 3rd and 4th cervical nerves providing branches to levator scapulae and trapezius muscles
(c) Dorsal scapular nerve (C5)
(d) Four cutaneous branches of cervical plexus (initial parts)
(e) Occipital artery
[Diagram: Contents of the Posterior Triangle of the Neck]
Further notes:
~ The spinal accessory nerve comprises the true content(s) of the posterior triangle and all others are behind or front of the fascial floor.
~ The most important contents of posterior triangle are: (a) third part of subclavian artery, (b) brachial plexus (cervical part), (c) spinal accessory nerve, and (d) lymph nodes.
~ All the important contents of the posterior triangle lie deep to the fascial carpet of the floor except spinal accessory nerve, which lies just underneath the roof. In operations on the posterior triangle all the structures except spinal accessory nerve are safe, provided fascial carpet of posterior triangle is left intact. The spinal accessory nerve can be injured in surgery requiring the removal or biopsy of lymph nodes in the posterior triangle of the neck.
State the contents of the subclavian/supraclavicular triangle.
(a) 3rd part of the subclavian artery
(b) Subclavian vein
(c) Terminal part of external jugular vein
(d) Trunks of brachial plexus
(e) Superficial transverse cervical, suprascapular, and dorsal scapular arteries
(f) Lymph nodes
[Diagram: Contents of the Posterior Triangle of the Neck]
Further notes:
~ The spinal accessory nerve comprises the true content(s) of the posterior triangle and all others are behind or front of the fascial floor.
~ The most important contents of posterior triangle are: (a) third part of subclavian artery, (b) brachial plexus (cervical part), (c) spinal accessory nerve, and (d) lymph nodes.
~ All the important contents of the posterior triangle lie deep to the fascial carpet of the floor except spinal accessory nerve, which lies just underneath the roof. In operations on the posterior triangle all the structures except spinal accessory nerve are safe, provided fascial carpet of posterior triangle is left intact. The spinal accessory nerve can be injured in surgery requiring the removal or biopsy of lymph nodes in the posterior triangle of the neck.
