Neck vessels

Common carotid artery

• Right from the brachiocephalic trunk behind the right sternoclavicular joint; left directly from the aortic arch.
• Ascends in the carotid sheath without branches; divides at the upper border of the thyroid cartilage (C3/C4).
• Can be compressed against the anterior (carotid, Chassaignac) tubercle of C6 to control bleeding.

Carotid sheath and relations

• Contents: common and internal carotid medially, internal jugular vein laterally, vagus behind and between them; ansa cervicalis on or in the front of the sheath.
• Behind and parallel to the sheath: the cervical sympathetic trunk on the prevertebral fascia.
• At its origin the external carotid lies anteromedial to the internal carotid, then becomes lateral as it ascends.

Internal versus external carotid

• External carotid branches: superior thyroid, ascending pharyngeal, lingual, facial, occipital, posterior auricular, then terminal maxillary and superficial temporal (in the parotid).
• Maxillary artery gives the middle meningeal artery and the sphenopalatine artery (posterior epistaxis). Superior thyroid artery runs with the external laryngeal nerve.
• Internal carotid: carotid canal, cavernous sinus, ophthalmic, posterior communicating and anterior choroidal arteries, then anterior and middle cerebral arteries.

Carotid sinus and carotid body

• Rise in pressure stretches the sinus, increases firing in Hering's nerve, which acts through the nucleus tractus solitarius to increase vagal (parasympathetic) and reduce sympathetic output: heart rate and blood pressure fall.
• Fall in pressure (haemorrhage, standing) reduces sinus firing, so sympathetic activity rises: tachycardia and vasoconstriction.
• Carotid sinus massage raises vagal tone to terminate SVT; avoid in the elderly with bruits. Carotid sinus hypersensitivity: syncope on head turning or with tight collars.
• Carotid body tumour (paraganglioma): painless pulsatile mass at the bifurcation, moves sideways but not vertically; splays the internal and external carotids.

Carotid disease

• Symptomatic stenosis: TIA or minor stroke in the territory (e.g. right arm and face weakness with a left internal carotid stenosis), amaurosis fugax. For 70–99% symptomatic stenosis, offer early carotid endarterectomy (ideally within 2 weeks); benefit is smaller at 50–69%.
• Nerves at risk in endarterectomy: hypoglossal (crosses both carotids), vagus and recurrent laryngeal, marginal mandibular branch of VII, superior laryngeal.
• Carotid dissection: neck pain, Horner syndrome, stroke in a young patient.

Subclavian artery

• Right from the brachiocephalic trunk, left from the arch; divided into three parts by scalenus anterior.

• The scapular (shoulder) anastomosis links suprascapular and dorsal scapular (subclavian) with the circumflex scapular (axillary).
• Vertebral artery: through the foramina transversaria of C6 to C1, over the atlas, through the foramen magnum, joining its partner to form the basilar artery.
• Subclavian steal: proximal subclavian stenosis makes the arm draw blood backwards down the ipsilateral vertebral artery; dizziness or syncope on exercising that arm, with lower blood pressure in it.

Internal jugular vein

• Begins at the jugular foramen as the continuation of the sigmoid sinus, with IX–XII close beside it and the internal carotid in front and medial; descends in the carotid sheath lateral to the carotids; joins the subclavian vein behind the sternoclavicular joint to form the brachiocephalic vein.
• Central line: apex of the triangle between the two heads of sternocleidomastoid and the clavicle, lateral to the carotid pulse, ideally with ultrasound. Place the patient head-down (Trendelenburg): it distends the vein and keeps venous pressure above atmospheric, reducing air embolism. Remove lines head-down or flat too. Other risks: carotid puncture, pneumothorax.
• JVP reflects right atrial pressure (patient at 45°, normally below about 4 cm above the sternal angle). Waves: a (atrial contraction, follows the P wave), c (tricuspid bulging, early systole near QRS), x descent, v (atrial filling), y descent.

External and anterior jugular veins

• External jugular vein: formed behind the angle of the mandible by the posterior auricular vein and the posterior division of the retromandibular vein; crosses sternocleidomastoid; pierces the deep fascia just above the middle of the clavicle to join the subclavian vein.
• Where it pierces the fascia, the vein wall is held open by the fascia; if cut there, it cannot collapse, and negative intrathoracic pressure sucks in air (sudden breathlessness, hypotension, churning "mill-wheel" murmur). Place the patient head-down and left side down and occlude the wound.
• Anterior jugular veins and the jugular venous arch lie in the suprasternal space; a common source of bleeding in tracheostomy.

Remember The internal carotid gives nothing in the neck; the external gives eight; IX supplies both the sinus and the body.

Exam trap A fall in blood pressure reduces carotid sinus firing and raises sympathetic drive.

Exam trap Position head-down for jugular cannulation to prevent air embolism.

How FCPS asks about this

• Level of the carotid bifurcation: upper border of the thyroid cartilage, C3/C4.
• Afferent nerve of the carotid sinus: glossopharyngeal (Hering's nerve).
• Effect of reduced carotid sinus pressure: less firing, more sympathetic activity, tachycardia.
• Structure behind and parallel to the carotid sheath: sympathetic trunk.
• 80% symptomatic internal carotid stenosis: early endarterectomy.
• Dizziness on arm exercise after subclavian stenosis: subclavian steal via the vertebral artery.
• Air embolism from a cut external jugular vein: fascia holds the wall open where it pierces the deep fascia.