Scalene Muscles & Subclavian Artery

• The root of the neck sits immediately above the thoracic inlet
• The area contains 3 muscles

Scalene Muscles

• The anterior scalene originates from the anterior tubercles of the cervical vertebrae and extends down to the scalene tubercle of the first rib (R1)
• The middle scalene attaches to R1 behind the groove for the subclavian artery
• The posterior scalene attaches inferiorly to the second rib (R2) and is often behind or fused with the scalenus medius
• All three scalene muscles are innervated by the dorsal rami of C4-6

Key Landmarks

• The anterior scalene is a key landmark
• Anterior to it is the phrenic nerve
• Posterior to it is the brachial plexus and the subclavian artery

Subclavian Artery

• The subclavian artery arises from the brachiocephalic artery on the right and from the arch of the aorta on the left
• The artery passes posterior to the scalenus anterior and crosses the first rib, grooving it
• After passing the distal margin of R1, it becomes the axillary artery
• It is divided into 3 parts

First Part of Subclavian Artery

• Extends from its origin to the medial border of the anterior scalene
• Gives rise to the following branches:
  • vertebral artery ascends to enter the transverse foramen of C6 and eventually enters the cranial cavity via the foramen magnum
  • thyrocervical trunk which branches into the inferior thyroid artery, suprascapular artery, and transverse (superficial) cervical artery
  • internal thoracic artery

Second Part of Subclavian Artery

• The portion of the subclavian artery found posterior to the anterior scalene
• Gives rise to the costocervical trunk, which branches into the superior intercostal artery (supplies the 1st and 2nd intercostal spaces) and the deep cervical artery (supplies muscles of the back of the neck)

Third Part of Subclavian Artery

• Extends from the lateral border of the anterior scalene to the distal border of the first rib
• It has no branches arising from it

Deep Visceral Compartment

• Includes the thyroid, parathyroids, and lymphatics

Thyroid Gland

• Descends from the foramen cecum of the tongue via the thyroglossal duct
• Consists of two lobes with a connecting isthmus
• A pyramidal lobe (or muscle - levator glandulae) may arise from the isthmus
• It is an endocrine organ heavily supplied with blood vessels which are freely anastomotic (sup/inf. thyroid, thyroidea ima)

Parathyroid Glands

• Tiny (6 mm) masses, 4-6 in number, embedded in the posterior aspect of the thyroid
• They are endocrine organs and are essential to life
• They get their blood supply from a small vessel off the inferior thyroid artery

Lymphatic Drainage

• The thoracic duct drains lymph into the venous system at the junction of the left internal jugular vein with the left subclavian vein
• It begins in the abdomen at the sac-like cysterna chyli
• Lymph from the lower extremities and abdomen are drained via the thoracic duct
• Just prior to entering the venous system, the thoracic duct accepts trunks from the left upper limb, left side of the head and neck and left side of the thorax
• Lymphatic trunks from the right side of the head and neck, right upper limb and right side of the thorax are drained into the right lymphatic duct
• It enters the venous system at the junction of the right internal jugular and subclavian veins
• These two major lymphatic vessels resemble veins and may contain blood in the cadaver due to backflow of venous blood into these vessels during pressure embalming

Lymph Nodes of Head and Neck

• Considered extracranial as the CNS has no lymphatic drainage
• There are two vertical chains of nodes: one superficial, the other deep
• The deep cervical nodes receive lymph from all the head and neck and runs from the base of the skull adjacent to the internal jugular vein in the carotid sheath
• There are so-called “horizontal rings” of lymph nodes that also drain into the deep cervical vertical chain
• Two important examples of this are:
  • the retropharyngeal nodes that lie predominantly in the retropharyngeal space between the pharynx and prevertebral fascia and receive lymph from the nasal cavity, soft palate and middle ear
  • the pretracheal, laryngeal / infrahyoid nodes that lie anterior to the visceral column of the neck and receive lymph from the larynx, trachea, pharynx, and esophagus.

Regional Groups of Lymph Nodes

• Occipital
• Mastoid (retroauricular)
• Parotid
• Buccal
• Submandibular (drains mouth/pharynx)
• Submental (drains tongue)
• Superficial cervical
• Laryngeal
• Tracheal
• All lymph drains to a regional group of nodes then eventually to the terminal group:
  • deep cervical group found along the carotid sheath adjacent to the internal jugular vein

Triangles of the Head and Neck

• Superficial triangles and fascially-defined spaces of the head and neck are two ways of localizing pathologic lesions
• They provide superficial anatomical relations for diseases
• Spaces of the head and neck have been popularized by tomography (CT) and magnetic resonance imaging (MRI) techniques
• They provide anatomical relationships at all depths and define compartments through which disease processes can extend
• They also provide a method for the differential diagnosis of mass lesions arising within an individual compartment

Lymphatic Drainage Pattern Within Each Triangle

• Understanding spaces and triangles allows correlation of radiologic findings with the surgical approach to a mass
• Enlargement of the specific lymph node group is an indication of where the tumorous mass would be located

Triangle, Lymph Node Group, and Primary Regions Drained

• Submental: Submental, Anterior tongue, central lower lip, anterior floor of the mouth and chin
• Submandibular: Submandibular, Anterior and middle tongue, lateral lower lip, upper lip, lateral nose, buccal region and submandibular gland
• Carotid: Superior deep cervical chain, Middle and posterior tongue, tonsil, nasopharynx, superior larynx and thyroid gland
• Occipital: Posterior superficial, Ant/mid/post cervical chain, superior tongue, tonsil, nasopharynx, deep cervical chain and superior larynx, thyroid gland, parotid and auricle region
• Subclavian: Inferior deep cervical, Inferior larynx, thyroid gland, chain trachea, and posterior scalp