Triangles of neck/ oral surgery courses

SEMINAR ON TRIANGLES
OF NECK
www.indiandentalacademy.com

 Anatomists use the term triangles of the neck to
describe the divisions created by the major muscles in
the region.
 The side of the neck presents a somewhat quadrilateral
outline, limited, above, by the lower border of the body
of the mandible, and an imaginary line extending from
the angle of the mandible to the mastoid process;
below, by the upper border of the clavicle; in front, by
the middle line of the neck; behind, by the anterior
margin of the Trapezius.

The triangles of the neck

ANATOMICAL FEATURES OF NECK
NECK CONSISTS OF FOLLOWING LAYER:-
 Skin
 Superficial fascia
Loose connective tissue + Platysma
 Deep fascia of neck (Deep cervical fascia)
i) Investing layer
ii) Pretracheal layer
iii) Prevertebral layer

Investing layer of deep fascia from below upwards
forms two pulleys to bind the respective tendons of the
digastric and omohyoid muscles.
Thyroid gland moves on swallowing because the
pretracheal fascia which splts to enclose it is attached
to the hyoid bone and the thyroid cartilage

 This neck is subdivided into two large triangles by the
Sternocleidomastoid, which passes obliquely across
the neck, from the sternum and clavicle below, to the
mastoid process and occipital bone above.
 The triangular space in front of this muscle is called
the Anterior triangle of the neck; and that behind it,
the Posterior triangle of the neck.

ANTERIOR TRIANGLES:-
 submental (smen)
 submandibular (sm)
 Muscular/visceral (mus)
 carotid (car)

 Subdivisions:
 I- Suprahyoid region – contains:
 A. Submental triangle
 B. Submandibular triangle
 II- Infrahyoid region – contains:
 A. Carotid triangle
 B. Muscular triangle

 Suprahyoid Region (Suprahyoid muscles)
 Digastric (anterior and posterior bellies)
 Stylohyoid – from styloid process to hyoid bone
 Geniohyoid – from inferior genial tubercles of
mandible to hyoid bone
 Mylohyoid – from mylohyoid line of mandible to
hyoid bone. It forms the floor of the mouth.
 Nerve supply:
 Anterior belly of digastric + Mylohyoid –
nerve to mylohyoid of the inferior alveolar
nerve from the mandibular branch of CN V
 Posterior belly of digastric + Stylohyoid – CN
VII
 Geniohyoid –CN XII
 Act on the mandible and adjust the position of hyoid
bone and larynx.

SUBMENTAL TRIANGLE
 The submental triangle is
located between the two
anterior digastric muscles
(abd) superior to the hyoid
bone, and the midline of the
neck, Floor is formed by the
mylohyoid muscle
 Structures found here are the
submental lymph node's that
drain the floor of the mouth
tip of the tongue and middle
lower lip and central incisors

 – A single triangle inferior to the mandible
 Boundaries:
 • Laterally – Rt. and Lt. anterior bellies of
digastric muscle
 • Base – hyoid bone
 • Apex – symphysis menti
 • Floor – Rt. and Lt. mylohyoid muscles that
meet in a midline fibrous raphe

 The mylohyoid muscle (mh) arise from the body of the
hyoid bone and insert into the mylohyoid line of the
inside of the mandible. This muscle aids in swallowing
and in depressing the mandible.
 Anterior jugular veins: Lying in the midline,
running from the submental triangle, they pierce the
deep fascia above manubrium. They pass between the
posterior border of the Sternocleidomastoid muscle
and the upper border of the clavicle to drain into the
external jugular veins in the posterior triangle of the
neck.

Submandibular (Digastric) Triangle:
 It between the posterior and anterior bellies of the
digastric muscle and inferior border of the mandible.
Its floor is formed by the mylohyoid, hyoglossus and
middle constrictor muscles.
 Continuous with the fossa for the parotid gland
 Mylohyoid muscle lies superior to the anterior belly
of the digastric
 Forms a sling passing from side to side from its
attachment to the internal surface of the mandible
(mylohyoid line)

 Forms the floor of mouth: It is attached from the
mylohyoid line to the superior aspect of body of
hyoid bone and the midline raphé.
 Around the free edge of this muscle lies the duct of
submandibular salivary gland which occupies a
significant part of the triangle
 Associated with the anterior belly of digastric, &
share the same innervation: Mylohyoid Br. of the
Inferior Alveolar N.

 Infrahyoid Region (Infrahyoid Strap Muscles )
 1. Sternohyoid – medially
 2. Omohyoid (superior belly) – laterally
 3. Thyrohyoid – superiorly
 4. Sternothyroid – inferiorly
 Nerve supply:
From ansa cervicalis except thyrohyoid supplied by C1
fibers carried by hypoglossal nerve.
 Stabilize and move the hyoid bone and larynx.

MUSCULAR TRIANGLE
 It lies between the superior belly of the omohyoid,
lower anterior margin of the sternocleidomastoid and
the median line of the neck.

 Contains the infrahyoid muscles and viscera of the
neck
i) Sternothyroid and sternohyoid muscles.
ii) Thyroid and parathyroid glands.

CAROTID TRIANGLE:
 It lies between the posterior belly of the digastric,
superior belly of the omohyoid and deep to the
sternocleidomastoid muscle. As the vascular area of
the neck, it is most noted for the carotid sheath and
its contents :
1. Common Carotid Artery .
2. Internal Jugular Vein .
3. Vagus N.
 Internal Jugular Vein collects blood from the brain,
face and neck and is usually the largest vein in the
neck.

 The Common Carotid Artery arises in the base of the
neck from the brachiocephalic artery on the right side
and directly from the arch of the aorta on the left side
in the superior mediastinum of the thorax. It passes
into the base of the neck through the thoracic inlet
bounded by T1 vertebral body, the sternum and first
rib and ascends into the carotid triangle.
 Bifurcation into the internal and external carotid
arteries occurs at the level of the upper border of the
thyroid cartilage(C4).

 Deep cervical lymph nodes lie along its course.
 Passes inferiorly through the carotid triangle receiving
many tributaries from surrounding structures.
 The vagus has an extensive distribution as it conveys
voluntary motor and sensory nerve fibres to structures
in the neck, and viscero-motor fibres to thorax and
abdomen. It enters the neck by exiting the skull
through the jugular foramen. In the carotid triangle it
lies behind and between the carotid and jugular
vessels

POSTERIOR TRIANGLE
The posterior triangle is crossed,
about 2.5 cm above the clavicle,
by the inferior belly of the
Omohyoid, which divides the
space into two triangles:
 an upper or occipital triangle
 a lower or subclavian triangle
(or supraclavicular triangle)

POSTERIOR TRIANGLE
 Boundaries of Posterior Triangle
 Anteriorly – posterior border of SCM
 Posteriorly – anterior border of Trapezius
 Inferiorly – middle 1/3 of clavicle
 Apex – at the superior nuchal line
 Roof – investing layer of deep cervical fascia
 Floor – prevertebral layer of deep cervical fascia
covering the following muscles from above downward:

Structures in Posterior Triangle
 spinal accessory (sa)
 brachial plexus (bp)
 transverse cervical (tc), subclavian and Suprascapular
arteries (ss).
 Cervical and supraclavicular lymph nodes

 The inferior belly of Omohyoid muscle divides the
posterior triangle into:
 1- Occipital triangle – larger and superiorly
 2- Supraclavicular (subclavian) – smaller and
inferiorly

BOUNDARIES OF OCCIPITAL TRIANGLE:
 Posterior : Trapezius m.
 Anterior : Sternocleidomastoid m.
 Inferior : Omohyoid m.
 Floor: Splenius Capitus m, Levator
Scapulae m, Scalenus Medius, and a
portion of Scalenus Anterior.
 Roof: superficial layer of Deep Investing
Fascia.

Sternocleidomastoid muscle and protection from
trauma

Subclavian vein puncture :- To administer parental
fluids, central venous pressure and often is the point of
entry to venous system for central line placement.
(Infraclavicular subclavian vein approach)
Puncture of internal jugular vein
To make measurements of pressure within
the right chamber of the heart.

Severance of the external jugular vein
Injury by knife produces venous air
embolism.
Prominence of external jugular vein
Internal barometer, diagnostic sign of heart
failure.
The investing layer of deep cervical fascia helps
prevents the spread of abscess.

The superficial layer of deep cervical fascia opposes the
extension of abscesses towards the surface, and pus
beneath it has a tendency to extend laterally. If the pus
is in the anterior triangle, it may find its way into the
mediastinum.
Pus behind the Prevertebral layer may extend towards
the lateral part of the neck and point in the lower part
of the posterior triangle or even descend in the axillary
sheath and point in the axilla. The pus may perforate
the Prevertebral layer and the buccopharyngeal fascia
to bulge into the pharynx as a retropharyngeal
abscess.

Injury to spinal accessory nerve can occur during
incisions given in the region of Sternocleidomastoid
for drainage of superficial abscess.
-- Wry neck Torticollis.
-- paralysis of Trapezius.
Congenital and spasmodic torticollis

The internal jugular vein is important –
i) It acts as a guide for surgeons during removal of deep cervical
lymph nodes.
ii) In mitral stenosis, a thrill may be felt at the roof of neck, in
supraclavicular fossa during systole.
iii) The vein can safely cannulated in cases of cardio-vascular
collapse by introducing needle in backward and upward direction
in triangular space between two heads of sternocleidomastoid.

Injury to the spinal accessory nerve in posterior
cervical triangle results in paralysis of Trapezius
muscle and shoulder dysfunction. (inability to raise the
arm above horizontal or shoulder droop)
Nerve crosses the posterior cervical triangle,
its superficial location makes it very susceptible to
injury.
Any surgery in the posterior triangle can injure the
nerve, such as cervical lymph node biopsy, excision of
benign masses and radical neck dissections for
malignancy.

Accessory nerve
Head

Iatrogenic spinal accessory nerve injuries need to be
diagnosed early and treated promptly to prevent a
severe and progressive debility of the shoulder girdle.
General practitioners need to be aware of the
possibility of injury to the spinal accessory nerve when
performing surgical procedures in the posterior
triangle of the neck. They may also perform an

important role in detecting injury to the spinal
accessory nerve in patients who present with shoulder
symptoms after neck
surgery.
Lymph node metastasis of cancer of floor of mouth
mainly distributes in I, II, III region; The patients with
negative cervical lymph node should be performed
lymph node dissection in I, II, III region (supra-half-
neck).

The triangles of neck assist the medical examiner in
accurately localizing a wound, tumor or swelling
unless the surgeon perfectly knows the boundaries and
the contents of the triangles.

References :-
 Keith. L . Moore : Clinical Oriented Anatomy: Head
and Neck: 4th
edition ; 1003-10024; Lippin- cott
Williams and Wilkins publication.
 Cervical lymphadenopathy: what radiologists need to
know, Vincent Chong, Department of Diagnostic
Radiology, Singapore General Hospital, Singapore;
Cancer Imaging. 2004; 4(2): 116–120.

 Shiozaki K, Abe S, Agematsu H: Anatomical study of
accessory nerve innervation relating to functional neck
dissection; J Oral Maxillofacial Surg. 2007
Jan;65(1):22-9.
 Richard.S.Snell : Clinical Anatomy, Head and Neck, 7th
edition :728-734 ; Lippin-cott Williams and Wilkins
publication.

 Australian Family Physician Vol. 35, No. 7, July
2006.
 Anand’s Human Anatomy ;Neck and Its Triangle: 1st
edition: 237-262; Arora Medical Book Publication.

Triangles of neck/ oral surgery courses

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