Neck anatomy - Anterior triangle - MRCS

MRCS Neck anatomy - Anterior triangle
Introduction
• The range of neck pathology and neck lumps requires a good understanding of the associated
anatomy.
• Classically the neck is arbitrarily organised into anterior and posterior triangles - separated by
the sternocleidomastoid (SCM) muscle:
Boundaries Anterior triangle Posterior triangle
Apex Jugular notch Union of SCM and trapezius
Base Lower border of mandible Middle third of clavicle
Anterior Midline of neck SCM
Posterior SCM Trapezius
• The anterior and posterior triangles can be further subdivided:
Post belly of
digastric
Stylohyoid
Mylohyoid
Ant belly of
digastric
Hyoglossus
Thyrohyoid
Constrictor
pharyngeus
Superior belly
omohyoid
Sternohyoid
Medius
Inferior
Anterior triangle regions
Submental
Submandibular
Muscular
Carotid
Sternocleidomastoid
Trapezius
Splenius
Levator
scapulae
Scalene
medius
Scalene
anterior
Inferior belly
omohyoid
Posterior triangle regions
Occipital
Supraclavicular

MRCS Neck anatomy - Anterior triangle
Submandibular region
• The region immediately below the mandible.
Boundaries Anterior triangle
Superior Body of mandible
Anterior Anterior belly of digastric
Posterior Posterior belly of digastric
Roof Skin, superficial fascia, platysma, deep fascia
Floor Mylohyoid muscle
Superficial submandibular structures:
Platysma - broad sheet of superficial muscle arising from
the fascia that overlaps sternocleidomastoid.
Facial vein
Cervical branch of facial nerve - supplies platysma
Submandibular gland:
• Accounts for ≈ 70% of salivary production
• Wharton’s duct (submandibular duct) arises from the
gland and passes between mylohyoid, hyoglossus and
genioglossus - eventually opening either the side of the
lingula frenulum.
• Parasympathetic supply - from a branch of the facial
nerve the chorda tympani (CNVII) which runs in the
sheath of the lingual nerve (branch of mandibular nerve
CNV3) to synapse at the submandibular ganglion -
which supplies the submandibular gland and lies on
hyoglossus.
Deep submandibular structures:
Facial artery
Lingual nerve -branch of mandibular nerve (CNV3)
Submandibular ganglion
Hypoglossal nerve (CNXII) - supplies all muscles of
tongue except palatoglossus.
Lingual artery

MRCS Neck anatomy - Anterior triangle
Submental region
• The region between the two anterior bellies of digastric.
Boundaries Anterior triangle
Superior Body of mandible
Anterior Midline
Posterior Anterior belly of digastric
Roof Skin, superficial fascia, platysma, deep fascia
Floor Mylohyoid muscle
• Contents:
• Submental lymph nodes.
• Superficial veins which form tributaries of the anterior jugular veins.
Carotid triangle
• Contains the carotid sheath.
Anterior belly of digastric
Submental lymph nodes
Stylohyoid
Posterior belly of digastric
Anterior jugular veins
Hyoid
Boundaries Anterior triangle
Superior Stylohyoid and posterior belly of digastric
Inferior Superior belly of omohyoid
Posterior Sternocleidomastoid
Roof Skin, superficial fascia, platysma, deep fascia
Floor Thyrohyoid, hyoglossus, constrictor
pharyngeus medius/inferior.

MRCS Neck anatomy - Anterior triangle
Carotid triangle
Hypoglossal nerve continues to supply all muscles
of the tongue except palatoglossus.
Superficial structures
The superficial veins are the first structures encountered
on removing the roof of the carotid triangle:
Common facial vein
Retromandibular vein
Posterior auricular vein
External jugular vein - commences at level of the angle of
the mandible runs obliquely over sternocleidomastoid. At
the midpoint of the clavicle - in the subclavian triangle
penetrates the deep fascia to drain into the subclavian
vein.
Internal jugular vein - deeper contained within the carotid
sheath (see below).
Anterior jugular vein (note not within carotid triangle)
Post removal/reflection of sternocleidomastoid -
overlying nerves and internal jugular vein
Hypoglossal nerve and branch of first cervical - a branch
of the first cervical nerve courses in the same sheath as
the hypoglossal nerve then leaves as two branches in the
carotid triangle:
1. Superior root of ansa cervicalis - supplies infrahyoid
muscles (see muscular triangle).
2. C1 nerve directly to thyrohyoid.
Ansa cervicalis - a loop of nerves derived from the
cervical plexus - receives supply from C1-3 nerve roots.
Innervates the infrahyoid muscles: sternohyoid,
sternothyroid and omohyoid.
Internal jugular vein - lies lateral to the internal carotid
and common carotid. At the root of the neck joins the
subclavian vein to form the brachiocephalic vein.
Combined with the carotid and vagus is contained within
the carotid sheath (see below).

MRCS Neck anatomy - Anterior triangle
Carotid triangle
Post removal of internal jugular vein
External carotid artery
Occipital artery
Facial artery
Lingual artery
Ascending pharyngeal artery
Superior thyroid artery
Internal carotid artery
Post removal of carotid artery
Vagus nerve - contained within carotid sheath (with
carotid and internal jugular vein)
Internal branch of superior laryngeal nerve - supplies
sensation to the epiglottis - irritation causes coughing.
External branch of superior laryngeal nerve- supplies
cricothyroid muscle - Clinical note: Susceptible to
damage during thyroidectomy as lies inferior and close to
superior thyroid artery (which is ligated during
thyroidectomy). Palsy results in loss of high pitch voice.

MRCS Neck anatomy - Anterior triangle
Muscular triangle
Boundaries Anterior triangle
Superior Superior belly of omohyoid
Anterior Midline of neck
Inferior Sternocleidomastoid
Roof Skin, superficial fascia, platysma, deep fascia
• The muscular triangle contains the infrahyoid muscles (also known as the strap muscles) whose
primary function is to depress the hyoid and larynx during swallowing.
• All are supplied by the ansa cervicalis (see above) except thyrohyoid which is directly supplied
by a branch of C1 nerve.
Superficial layer
Superior belly omohyoid - omohyoid consists of 2 bellies
separated by an intermediate tendon. It arises from the
scapula. The inferior belly then courses along the clavicle
bound by a fibrous expansion. Behind the
sternocleidomastoid it becomes tendinous then courses
vertically upwards as the superior belly to insert onto the
hyoid.
Sternohyoid- sternum to hyoid
Deep layer
Thyrohyoid - thyroid cartilage to hyoid
Sternothyroid - sternum to thyroid cartilage
Thyroid - see separate revision sheet
Inferior belly omohyoid