The Anterior and Posterior Triangles of the Neck

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The Anterior and Posterior Triangles of the Neck
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Anterior Triangle of the Neck
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BONY SKELETON OF THE NECK

• Like other regions of the body, the neck has a
  central bony skeletal core upon which other
  structures attach or are related. The bones of
  the neck consist of the base of the skull and the
  7 cervical vertebrae.
• If we take a look at the base of the skull, the
  major parts that are related to the upper neck
  are the
• Foramen magnum
• Occipital condyle (articulates with the superior
  process of the atlas.
• External occipital protuberance
• Mastoid process

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• Below the base of the skull, you will find the
  vertebral column. The top vertebrae (7 cervical)
  provide support for the neck structures. You will
  also note that these vertebrae allow passage of
  an important arterial supply to the brain and
  brain stem, the vertebral artery.

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• The first cervical vertebra is the atlas and is
  considered an atypical cervical vertebra because
  it has no body or spinous process. It articulates
  with the occipital condyles of the skull above it
  and with the superior articular processes of the
  axis below it. It also articulates with the dens
  of the axis below. If viewed from above, you can
  identify the following parts of the atlas
• Anterior arch
• Anterior tubercle
• Superior articular process (articulate with the
  occipital condyle of the skull)
• Foramen transversarium
• Transverse process
• Posterior arch
• Posterior tubercle
• Vertebral canal (continuous with the foramen
  magnum at the base of the skull). The brain stem
  continues inferiorly as the spinal cord at the
  margin of the foramen magnum.

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• The axis is the second cervical vertebra. This
  vertebral is also called an atypical vertebra
  because it has an upward projection called the
  dens that articulates with the inner aspect of
  the anterior arch of the atlas just posterior to
  the anterior tubercle. Some of the identifiable
  parts are the
• dens
• body
• superior articular process
• transverse process with its vertebral foramen
• pedicle
• lamina
• bifid spine

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• The 3rd, 4th, 5th, and 6th cervical vertebrae are
  known as the typical cervical vertebrae because
  they all have the same characteristics and except
  for the foramen for the vertebral artery similar
  to other typical vertebrae of the spinal cord.
  These characteristics are
• body
• pedicle
• foramen for vertebral artery
• superior articular process
• lamina
• spinous process (bifid in case of cervical
  vertebrae)
• vertebral canal
• transverse process (consists of a groove that
  carries a cervical spinal nerve and, of course
  the foramen for the vertebral artery)

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• The 7th cervical vertebra starts to pick up
  characteristics of the upper thoracic vertebrae.
• Differences from other cervical vertebrae
• no foramen for the vertebral artery
• After the vertebral artery arises from the
  subclavian artery, it enters the transverse
  foramen of the 6th cervical vertebra bypassing
  the 7th
• may not have a bifid spinous process
• the spinous process of the 7 cervical vertebra is
  longer than the other cervical vertebrae
• it is not buried under the ligamentum nuchae of
  the neck so it is easy to see and to palpate and
  is called the vertebra prominens
• can serve as a surface landmark demarcating the
  neck (cervical) from the thoracic regions of the
  body.

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Anterior Neck
Major Landmarks

• Common carotid artery (cc)
• Internal carotid artery (ic)
• External carotid artery (ec)
• Carotid sinus

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• Superficial structures from the lateral view of
  the neck.
• sternomastoid
• trapezius
• occipital lymph nodes (on)
• retroauricular lymph nodes (ran)
• superficial cervical lymph nodes (scn)
• submental lymph nodes (smn)
• buccal lymph nodes (bn)
• parotid lymph nodes (pn)
• submandibular lymph nodes (not labeled but uner
  angle of mandible)

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• Abnormalities of the superficial neck
• Swollen lymph nodes sign of an infection in an
  area that is drained by the nodes
• The superficial group of nodes in the neck drain
  the skin of the face and nose, scalp and external
  ear.
• The submental nodes also drain the tip of the
  tongue.
• Deeper regions of the head and neck drain into a
  deep group of lymph nodes and are less palpable.
• Other important landmarks
• the cartilages of the larynx and trachea
• the thyroid gland is closely associated with the
  cricoid cartilage
• the tracheal rings
• the carotid artery
• carotid artery pulse can be felt by pushing
  lateral to the upper border of the thyroid
  cartilage just under the anterior edge of the
  sternomastoid muscle.

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Anterior Triangle of the Neck In Detail
The neck is arbitrarily subdivided into two
triangles by the sternocleidomastoid muscle

• Anterior Triangle
• submental (smen)
• submandibular (sm)
• muscular-visceral (mus)
• carotid (car)
• Posterior Triangle
• occipital
• supraclavicular  (omoclavicular)

Starting above the hyoid bone in the anterior
triangle, we have two small triangles submental
and submandibular (or digastric). We will start
this study by looking at the submandibular
triangle first then the submental.
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Triangles within the Anterior Triangle of the Neck
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The Submandibular Triangle

• Boundaries
• mastoid mandible above
• anterior belly of digastric anteriorly (abd)
• posterior belly of digastric (pbd)
• stylohyoid posteriorly (sh)

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• The superficial (roof) structures of the
  submandibular region are  
• platysma
• facial vein (fv)
• cervical branch of facial nerve (cbf)

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• Removal of the superficial structures displays
  the submandibular salivary gland itself.

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• contents of the submandibular triangle are
  structures passing through
• facial artery (fa)
• lingual nerve and submandibular ganglion (ln)
• submandibular duct (smd)
• lingual artery (la)
• hypoglossal nerve (XII)
• the lingual nerve and submandibular duct pass
  through a gap between the hypoglossal (hg) and
  mylohyoid (mh) muscles
• the lingual artery passes deep to the hyoglossus
  muscle.

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The Submental Triangle

• located between the two anterior digastric
  muscles (abd).
• Structures
• submental lymph node(s) (ln) - drain the floor of
  the mouth.
• mylohyoid muscle (mh) arise from the body of the
  hyoid bone and insert into the mylohyoid line of
  the inside of the mandible.
• aids in swallowing and in depressing the
  mandible.

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The Carotid Triangle

• The boundaries of the carotid triangle are
• posterior belly of digastric muscle (pbd)
• superior belly of the omohyoid muscle (so)
• anterior border of sternomastoid muscle (st)

Starting from the most superficial aspects of the
carotid triangle, we will point out the items
that are related to it.
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Roof of the Carotid Triangle

• The first layer, under the skin and superficial
  fascia includes the platysma, which forms the
  roof of the carotid triangle. Note the location
  of the carotid triangle in purple.

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Veins of the Carotid Triangle

• With the roof removed, here are the boundaries of
  the carotid triangle and the superficial veins
  related to it
• common facial vein (cf) (within carotid triangle)
  
• Other structures near by
• retromandibular vein (rm)
• posterior auricular vein (pav)
• facial vein (fv)
• external jugular vein (ej)
• anterior jugular vein (aj)

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Nerves within the Carotid Triangle

• The nerves that enter the carotid triangle and
  that lie superficial to the internal jugular
  vein, internal and external carotid arteries are
  
• hypoglossal (XII)
• C1 root of ansa cervicalis (C1)
• C1 fibers running with hypoglossal nerve (nerve
  to thyrohyoid muscle (nth)
• C2-C3 root of ansa cervicalis
• ansa cervicalis (ac)

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Nerves within the Carotid Triangle
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Reflection of sternomastoid and removal of common
facial vein

• cca-common carotid artery eca-external carotid
  artery
• sta-supterior thyroid artery
• oa-occipital artery
• la-lingual artery
• fa-facial artery
• ica-internal carotid artery

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Arteries in the Carotid Triangle
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Floor of the carotid triangle

• The floor is the the deepest aspect of the
  carotid triangle.
• The muscles, at this level, are the middle and
  lower pharyngeal constrictors (mpc and ipc).
• The structures seen passing through this level
  are
• superior laryngeal nerve, a branch of the vagus
  its 2 terminal branches
• internal laryngeal (ilb--sensory to upper part of
  the larynx)
• external laryngeal (elb--motor to the cricoid
  muscle)

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Muscular or Visceral Triangle

• The muscular triangle has the following
  boundaries
• mid line of neck (1)
• superior belly of omohyoid (2)
• sternomastoid (3)
• The muscles forming and within the triangle are
  seen in image labeled (these muscles are often
  called the strap muscles, for obvious reasons
• superficial layer
• sternohyoid (sh)
• superior belly of omohyoid (oh)
• deep layer
• thyroid (th)
• sternothyroid (st)

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Thyroid gland and its arterial supply

• When the strap muscles are reflected, you can see
  the thyroid gland (tg) with its arteries
  (superior thyroid artery from the external
  carotid (sta) and the inferior thyroid artery
  from the thyrohyoid trunk from the subclavian
  (ita).

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• If the thyroid gland is reflected laterally, the
  structures making up the larynx and trachea are
  seen
• thyrohyoid membrane (thm)
• thyroid cartilage (Adam's apple)(tc)
• cricothyroid membrane and ligament (ctm)
• cricoid cartilage (cc)
• tracheal rings (tr)

Cartilages and membranes
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Anterior View of Thyroid Gland

• The thyroid gland is hidden under the sternohyoid
  and sternothyroid muscles and consists of two
  lobes and an isthmus.
• An occasional pyramidal lobe extends upward near
  the mid line.
• The inferior thyroid artery is closely associated
  with the recurrent laryngeal nerve (rln).

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Deep Surface of Thyroid Gland

• Four small reddish-brown pea-sized glands may be
  seen on the deep surface of the thyroid gland.
• These are the superior and inferior parathyroid
  glands (ptg).
• Also note the close relationship of the recurrent
  laryngeal nerves to the thyroid gland and
  inferior thyroid artery (rln, ita).

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Clinical Considerations

• The cricothyroid ligament and membrane are
  frequently pierced in emergency situations to
  open the airway.
• It has been known that an empty ball-point pen or
  a hollow stem has been used in the field to save
  lives, where an air passage has been closed above
  this region.

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Structures Found At the Root of the Neck

• After the sternoclavicular joint is
  disarticulated the structures located at the root
  of the neck can be identified.
• The root of the neck is bounded by the manubrium
  of the sternum anteriorly, the first rib
  laterally and the first thoracic vertebra
  posteriorly.
• All structures passing from the head through the
  neck to lower regions pass through this area as
  well as structures arising in the thoracic cavity
  and passing out through this region.

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• Most anterior structures
• brachiocephalic vein
• vertebral vein
• internal jugular vein
• subclavian vein
• thoracic duct
• thymus gland

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• The next layer can be considered the artery-nerve
  layer  
• lung
• vagus nerve
• common carotid artery
• subclavian artery
• ansa subclavius
• thyrocervical trunk
• vertebral artery
• internal thoracic artery
• trachea
• esophagus

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• The upper lobe of the lung (1) extends into the
  neck region. This is clinically important for
  anyone entering this region surgically since the
  lung can be punctured if the surgeon isn't
  careful.

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• The posterior part of the root of the neck is
  made up of the anterior surface of the body of
  the 1st thoracic vertebra with its anterior
  longitudinal ligament (in gray). When observing
  this area, you can see the nerves  
• ventral ramus of C8
• ventral ramus of T1
• lower trunk of brachial plexus
• stellate ganglion (inferior cervical 1st
  thoracic ganglia)

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Table of Muscles