Neck Anatomy Flashcards
(27 cards)
Digastric triangle
The digastric triangle is bordered above by the lower border of the mandible and its projection to the mastoid process, posteroinferiorly by the posterior belly of digastric and by stylohyoid, and anteroinferiorly by the anterior belly of digastric. It is covered by the skin, superficial fascia, platysma and deep fascia, which contain branches of the facial and transverse cutaneous cervical nerves. Its floor is formed by mylohyoid and hyoglossus. The anterior region of the digastric triangle contains the submandibular gland, which has the facial vein superficial to it and the facial artery deep to it. The submental and mylohyoid arteries and nerves lie on mylohyoid. The submandibular lymph nodes are variably related to the submandibular gland. The posterior region of the digastric triangle contains the lower part of the parotid gland. The external carotid artery, passing deep to stylohyoid, curves above the muscle, and overlaps its superficial surface as it ascends deep to the parotid gland before entering it. The internal carotid artery, internal jugular vein and vagus nerve lie deeper and are separated from the external carotid artery by styloglossus, stylopharyngeus and the glossopharyngeal nerve.
Submental triangle
The single submental triangle is demarcated by the anterior bellies of both digastric muscles. Its apex is at the chin, its base is the body of the hyoid bone and its floor is formed by both mylohyoid muscles. It contains lymph nodes and small veins that unite to form the anterior jugular vein.
Carotid triangle
The carotid triangle is limited posteriorly by sternocleidomastoid, anteroinferiorly by the superior belly of omohyoid and superiorly by stylohyoid and the posterior belly of digastric. In the living (except the obese), the triangle is usually a small visible triangular depression, sometimes best seen with the head and cervical vertebral column slightly extended and the head contralaterally rotated. The carotid triangle is covered by the skin, superficial fascia, platysma and deep fascia containing branches of the facial and cutaneous cervical nerves. The
hyoid bone forms its anterior angle and adjacent floor. Parts of thyrohyoid, hyoglossus and inferior and middle pharyngeal constrictor muscles form its floor. The carotid triangle contains the upper part of the common carotid artery and its division into external and internal carotid arteries. Overlapped by the anterior margin of sternocleidomastoid, the external carotid artery is first anteromedial, then anterior to the internal carotid artery. Branches of the external carotid artery are encountered in the carotid triangle. Thus the superior thyroid artery
runs anteroinferiorly, the lingual artery anteriorly with a characteristic upward loop, the facial artery anterosuperiorly, the occipital artery posterosuperiorly and the ascending pharyngeal artery medial to the internal carotid artery. The superior thyroid, lingual, facial, ascending pharyngeal and sometimes the occipital veins correspond to the branches of the external carotid artery, and all drain into the internal jugular vein. The hypoglossal nerve crosses the external and internal carotid arteries.
Carotid sheath
The conventional description of the carotid sheath is that it is a condensation of deep cervical fascia around the common and internal carotid arteries, internal jugular vein, vagus nerve and ansa cervicalis. It is thicker around the arteries than the vein, an arrangement that allows the vein to expand. Peripherally, the sheath is connected to adjacent fascial layers by loose areolar tissue.
Danger space
The danger space lies between the alar and prevertebral fascia, and extends from the skull base down to the posterior mediastinum, where the alar, visceral and pre-vertebral layers of deep cervical fascia fuse. The potential space so created is closed superiorly, inferiorly and laterally; infections can only enter by penetrating its walls. The danger space is so called because its loose areolar tissue offers a potential route for the rapid downward spread of infection, primarily from the retropharyngeal, parapharyngeal or pre-vertebral spaces, to the posterior
mediastinum.
Cellulitis in the neck
The most common causes of cellulitis of the neck are infections arising from the region of the mandibular molar teeth and the palatine tonsils. Several fascial spaces are accessible from this area, and several anatomical factors contribute to the spread of infection. Thus, the apices of the second and, more especially, the third, mandibular molar teeth are often close to the lingual surface of the mandible. The apices of the roots of the third mandibular molars are usually, and the second molars are often, below the attachment of mylohyoid on the inner aspect of
the mandible and so drain directly into the submandibular tissue space. The posterior free border of mylohyoid is close to the sockets of the third mandibular molars, and at this point, the floor of the mouth consists only of mucous membrane covering part of the submandibular salivary gland. Any virulent periapical infection of the mandibular third molar teeth may therefore penetrate the lingual plate of the mandible and is then at the entrance to the submandibular and sublingual spaces anteriorly, and the parapharyngeal and pterygoid spaces posteriorly. Infection in this area may also spread from an acute pericoronitis, particularly when the deeper tissues are opened to infection by extraction of the tooth during the acute phase. In general, cellulitis around the jaw is only likely to develop when the tissues are infected by virulent and invasive organisms at a point where there is access to the fascial spaces; the predisposing causes do not often coincide, and cellulitis is therefore uncommon. All forms of cellulitides of the neck or deep neck space infections are potentially very serious. Obstruction of the upper airway develops as a result of inflammation and oedema, compounded by salivary
pooling consequent on dysphagia, and this can be quite catastrophic.
Increased rigidity and reduced compliance of the tissues make manoevres such as manual anterior jaw thrust or laryngoscopy almost impossible. Specialized techniques, e.g. flexible fibreoptic-assisted tracheal intubation or surgical tracheostomy under local anaesthesia, are usually required to provide safe general anaesthesia to facilitate the surgical drainage and treatment of the cellulitis or deep space abscess.
Sternocleidomastoid
Sternocleidomastoid descends obliquely across the side of the neck and forms a prominent surface landmark, especially when contracted. The muscle is attached inferiorly by two heads. The medial or sternal head is rounded and tendinous, arises from the upper part of the anterior surface of the manubrium sterni, and ascends posterolaterally. The lateral or clavicular head, which is variable in width and contains muscular and fibrous elements, ascends almost vertically from the superior surface of the medial third of the clavicle.
Sternocleidomastoid receives its blood supply from branches of the occipital and posterior auricular arteries (upper part of muscle), the superior thyroid artery (middle part of muscle) and the suprascapular artery (lower part of muscle)
Sternocleidomastoid is supplied by the accessory nerve.
Acting alone, each sternocleidomastoid will tilt the head towards the ipsilateral shoulder, simultaneously rotating the head so as to turn the face towards the opposite side. A more common visual movement is a level
rotation from side to side, and this probably represents the most frequent use of the sternocleidomastoids. The two sternocleidomastoids are also used to raise the head when the body is supine; when the head is fixed, they help to elevate the thorax in forced inspiration
Digastric muscle
Digastric has two bellies and lies below the mandible, extending from the mastoid process to the chin. The posterior belly, which is longer than the anterior, is attached in the mastoid notch of the temporal bone, and passes downwards and forwards. The anterior belly is attached to the digastric fossa on the base of the mandible near the midline, and slopes downwards and backwards. The two bellies meet in an intermediate tendon that perforates stylohyoid and runs in a fibrous sling attached to the body and greater cornu of the hyoid bone; it is sometimes lined by a synovial sheath. The two bellies of digastric mark out the borders of the submandibular triangle.
The posterior belly is supplied by the posterior auricular and occipital arteries. The anterior belly of digastric receives its blood supply chiefly from the submental branch of the facial artery.
The anterior belly of digastric is supplied by the mylohyoid branch of the inferior alveolar nerve, and the posterior belly is supplied by the facial nerve. The different innervation of the two parts reflects their separate derivations from the mesenchyme of the first and second branchial arches.
Digastric depresses the mandible and can elevate the hyoid bone. The posterior bellies are especially active during swallowing and chewing.
Common carotid artery
The common carotid arteries differ on the right and left sides with respect to their origins. On the right, the common carotid arises from the brachiocephalic artery as it passes behind the sternoclavicular joint. On the left, the common carotid artery comes directly from the arch of the aorta in the superior mediastinum. The right common carotid, therefore, has only a cervical part whereas the left common carotid has cervical and thoracic parts. Following a similar course on both sides, the common carotid artery ascends, diverging laterally from behind the sternoclavicular joint to the level of the upper border of the thyroid cartilage of the larynx (C3–4 junction), where it divides into external and internal carotid arteries. This bifurcation can sometimes be at a
higher or lower level. The angle of bifurcation remains unchanged from infancy to adulthood.
External carotid artery
The external carotid artery begins lateral to the upper border of the thyroid cartilage, level with the intervertebral disc between the third and fourth cervical vertebrae. A little curved and with a gentle spiral, it first ascends slightly forwards and then inclines backwards and a little laterally, to pass midway between the tip of the mastoid process and the angle of the mandible. Here, in the substance of the parotid gland behind the neck of the mandible, it divides into its terminal branches, the superficial temporal and maxillary arteries. As it ascends, it gives off several large branches and diminishes rapidly in calibre. At its origin, it is in the carotid triangle and lies anteromedial to the internal carotid artery. It later becomes anterior, then lateral, to the internal carotid as it ascends. At mandibular levels, the styloid process and its attached structures intervene between the vessels; the internal carotid is deep, and the external carotid superficial, to the styloid process.
Branches of the external carotid artery
The external carotid artery has eight named branches distributed to
the head and neck. The superior thyroid, lingual and facial arteries arise
from its anterior surface, the occipital and posterior auricular arteries
arise from its posterior surface, and the ascending pharyngeal artery
arises from its medial surface. The maxillary and superficial temporal
arteries are its terminal branches within the parotid gland.
Internal carotid artery
The internal carotid artery supplies most of the ipsilateral cerebral hemisphere, eye and accessory organs, forehead and, in part, the nose. From its origin at the carotid bifurcation (where there is usually a carotid sinus), it ascends in front of the transverse processes of the upper three cervical vertebrae to the inferior aperture of the carotid canal in the petrous part of the temporal bone. Here, it enters the cranial cavity and turns anteriorly through the cavernous sinus in the carotid groove on the side of the body of the sphenoid bone. It terminates below the anterior perforated substance by division into the anterior and middle cerebral arteries. It may be divided conveniently into cervical, petrous, cavernous and cerebral parts.
Subclavian artery
The right subclavian artery arises from the brachiocephalic trunk,
the left from the aortic arch. For description, each is divided into a first part,
from its origin to the medial border of scalenus anterior; a second part
behind this muscle; and a third part from the lateral margin of scalenus
anterior to the outer border
First part of right subclavian artery
The right subclavian artery branches from the brachiocephalic trunk
behind the upper border of the right sternoclavicular joint, and passes
superolaterally to the medial margin of scalenus anterior. It usually
ascends 2 cm above the clavicle but this varies.
The artery is deep to the skin, superficial fascia, platysma, supraclavicular nerves, deep fascia, clavicular attachment of sternocleidomastoid, sternohyoid and sternothyroid. It is at first behind the origin of the right common carotid artery; more laterally, it is crossed by the vagus nerve, the cardiac branches of the vagus and the sympathetic chain, and by internal jugular and vertebral veins; the subclavian sympathetic loop encircles it. The anterior jugular vein diverges laterally in front of it, separated by sternohyoid and sternothyroid. Below and
behind the artery are the pleura and pulmonary apex; they are separated from the artery by the suprapleural membrane, the ansa subclavia, a small accessory vertebral vein and the right recurrent laryngeal nerve,
which winds round the lower and posterior part of the vessel.
First part of left subclavian artery
The first part of the left subclavian artery springs from the aortic arch, behind the left common carotid, level with the disc between the third and fourth thoracic vertebrae. It ascends into the neck, and then arches laterally to the medial border of scalenus anterior.
Relations: In the neck, near the medial border of scalenus anterior, the artery is crossed anteriorly by the left phrenic nerve and the termination of the thoracic duct. Otherwise, anterior relations are the same as those of the first part of the right subclavian artery. Posteriorly and inferiorly, the relations of both vessels are identical but the left recurrent laryngeal nerve, medial to the left subclavian artery in the thorax, is not directly related to its cervical part.
Second part of subclavian artery
The second part of the subcla-ian artery lies behind scalenus anterior; it is short and constitutes the highest part of the vessel.
Relations: The skin, superficial fascia, platysma, deep cervical fascia, sternocleidomastoid and scalenus anterior are anterior. The right phrenic nerve is often described as being separated from the second part of the subclavian artery by scalenus anterior, whereas it crosses the first part of the left subclavian artery. However, both nerves may sometimes lie anterior to the muscle. The suprapleural membrane, pleura and lung, and the lower trunk of the brachial plexus are posteroinferior; the upper and middle trunks of the plexus are superior; and the subclavian vein is anteroinferior, separated by scalenus anterior.
Third part of subclavian artery
The third part of the subclavian artery descends laterally from the lateral margin of scalenus anterior to the outer border of the first rib, where it becomes the axillary artery. It is the most superficial part of the artery and lies partly in the supraclavicular triangle, where its pulsations may be felt and it may be compressed. The third part of the subclavian artery is the most accessible segment of the artery. Since the line of the posterior border of sternocleidomastoid approximates to the (deeper) lateral border of scalenus anterior, the artery can be felt in the anteroinferior angle of the posterior triangle. It can only be effectively compressed against the first rib: with the shoulder depressed, pressure is exerted down, back and medially in the angle between sternocleidomastoid and the clavicle. The palpable trunks of the brachial plexus may be injected with local anaesthetic allowing major surgical procedures to the arm.
Relations: The skin, superficial fascia, platysma, supraclavicular nerves and deep cervical fascia are anterior. The external jugular vein crosses its medial end and here receives the suprascapular, transverse cervical and anterior jugular veins, which collectively often form a venous plexus. The nerve to subclavius descends between the veins and the artery; the latter is terminally behind the clavicle and subclavius, where it is crossed by the suprascapular vessels. The subclavian vein is anteroinferior and the lower trunk of the brachial plexus is posteroinferior,
between the subclavian artery and the scalenus medius (and on the first rib). The upper and middle trunks of the brachial plexus (which are palpable here) and the inferior belly of omohyoid are superolateral. The first rib is inferior. The right subclavian artery may arise above or below sternoclavicular level; it may be a separate aortic branch and be the first or last branch of the arch. When it is the first branch, it is in the position of a brachiocephalic trunk. When it is the last branch, it arises from the left end of the arch, and ascends obliquely to the right behind the trachea, oesophagus and right common carotid to the first rib. When this happens, the right recurrent laryngeal nerve hooks round the common carotid artery. Sometimes, when the right subclavian artery is the last aortic branch, it passes between the trachea and oesophagus and can cause dysphagia, a condition known as dysphagia lusoria. It may perforate scalenus anterior, and very rarely may pass anterior to it. Sometimes, the subclavian vein accompanies the artery behind scalenus anterior. The artery may ascend as high as 4 cm above the clavicle or it may reach only its upper border. The left subclavian artery is occasionally combined at its origin with the left common carotid artery.
External jugular vein
The external jugular vein mainly drains the scalp and face, although it also drains some deeper parts. The vein is formed by the union of the posterior division of the retromandibular vein with the posterior auricular vein and begins near the mandibular angle just below or in the parotid gland. It descends from the angle to the midclavicle, running obliquely, superficial to sternocleidomastoid, to the root of the neck. Here, it crosses the deep fascia and ends in the subclavian vein, lateral or anterior to scalenus anterior. There are valves at its entrance into the subclavian but they do not prevent regurgitation. Its wall is adherent to the rim of the fascial opening. It is covered by platysma, superficial fascia and skin, and is separated from sternocleidomastoid by deep cervical fascia. The vein crosses the transverse cutaneous nerve and lies parallel with the great auricular nerve, posterior to its upper half. In size, the external jugular vein is inversely proportional to the other veins in the neck and may be double. Between the entrance into the subclavian vein and a point approximately 4 cm above the clavicle, the vein is often dilated, producing a so-called sinus.
Anterior jugular vein
The anterior jugular vein arises near the hyoid bone from the confluence
of the superficial submandibular veins. It descends between the midline
and the anterior border of sternocleidomastoid. Turning laterally, low
in the neck, deep to sternocleidomastoid but superficial to the infrahyoid
strap muscles, it either joins the end of the external jugular vein
or may enter the subclavian vein directly. In size, it is
usually inverse to the external jugular vein. It communicates with the
internal jugular vein, and receives the laryngeal veins and sometimes a
small thyroid vein. There are usually two anterior jugular veins, united
just above the manubrium by a large transverse jugular arch, receiving
the inferior thyroid tributaries. They have no valves and may be replaced
by a midline trunk.
Internal jugular vein
The internal jugular vein collects blood from the skull, brain, superficial
parts of the face and much of the neck. It begins at the cranial base in
the posterior compartment of the jugular foramen, where it is continuous
with the sigmoid sinus. At its origin, it is dilated as the superior
bulb, which lies below the posterior part of the tympanic floor. The
internal jugular vein descends in the carotid sheath, and unites with
the subclavian vein, posterior to the sternal end of the clavicle, to form
the brachiocephalic vein. Near its termination, the vein
dilates into the inferior bulb, above which is a pair of valves. The jugular
bulb is a dynamic structure; it forms after 2 years of age and its size
stabilizes in adulthood.
Facial vein
From the face, it passes over the surface of masseter, crosses the body of the mandible and enters the neck, where it runs obliquely back under platysma. Here it lies superficial to the submandibular gland, digastric and stylohyoid. Just anteroinferior to the mandibular angle, it is joined by the anterior di-ision of the retromandibular vein, and then descends superficial to the loop of the lingual artery, the hypoglossal nerve and external and internal carotid arteries, to enter the internal jugular near the greater cornu of the hyoid bone, i.e. in the upper angle of the carotid triangle. Near its end, a large branch often descends along the anterior border of
sternocleidomastoid to the anterior jugular vein. Its uppermost segment, above its junction with the superior labial vein, is often termed the angular vein.
Lingual vein
The lingual veins follow two routes. The dorsal lingual veins drain the
dorsum and sides of the tongue, join the lingual veins accompanying
the lingual artery between hyoglossus and genioglossus, and enter the
internal jugular near the greater cornu of the hyoid bone. The deep
lingual vein begins near the tip of the tongue and runs back, lying near
the mucous membrane on the inferior surface of the tongue. Near the
anterior border of hyoglossus, it joins a sublingual vein, from the sublingual
salivary gland, to form the vena comitans nervi hypoglossi, which runs back
between mylohyoid and hyoglossus with the hypoglossal nerve to join the facial,
internal jugular or lingual vein.
Lymphatic drainage of the neck
Many vessels draining the superficial cervical tissues skirt the borders of sternocleidomastoid to reach the superior or inferior deep cervical nodes. Others pass to the superficial cervical and occipital nodes. Lymph from the superior region of the anterior triangle drains to the submandibular and submental nodes. Vessels from the anterior cervical skin inferior to the hyoid bone pass to the anterior cervical lymph nodes near the anterior jugular veins. Their efferents go to the deep cervical nodes of both sides, including the infrahyoid, prelaryngeal and pretracheal groups. An anterior cervical node often occupies the suprasternal space. Lymph from tissues of the head and neck internal to the deep fascia drains to the deep cervical nodes directly or through outlying groups that include the retropharyngeal, paratracheal, lingual, infrahyoid, prelaryngeal and pretracheal groups. The lymphatic drainage associated with the nasal region, larynx and oral cavity is described in the appropriate regions. The deep cervical lymphatic nodes lie alongside the carotid sheath, and form superior and inferior groups.
