Lecture: 5 Head and neck Dr. Omar Riadh
18-10-2017
The carotid sheath:-
It is a fascial sheath encloses the internal jugular vein, common carotid artery, vagus nerve and the roots of ansa cervicalis. The sympathetic trunk is in the posteromedial wall of the sheath. The sheath attached superiorly to the jugular foramen and carotid canal, in the sheath the artery is medial, the vein is lateral and the nerve is posterior and in between the vessels.Common carotid artery:-
The right common carotid artery arises from the brachiocephalic trunk behind the right sternoclavicular joint, while the left common carotid artery arises from the arch of the aorta and ascends to enter the neck posterior to the left sternoclavicular joint. From the joint each artery ascends to the upper border of thyroid cartilage at the level between the 3rd and 4th cervical vertebra, here it divides into internal and external carotid artery. both arteries are overlapped by sternoceidomastoid muscle, infrahyoid muscles and the thyroid gland but not on their upper portion.
The common carotid artery has no branches, the internal carotid artery also has no branches in the neck and continues in the carotid sheath with the internal jugular vein to the base of skull.
Relation of common carotid artery:-
Anteriorly:- Skin, fascia, sternocleidomastoid muscle, sternohyoid, sternothyroid and superior belly of omohyoid muscle.
Posteriorly:-
Transverse process of lower four cervical vertebra.
Prevertebral muscles.
Sympathetic trunk.
Vertebral vessels.
Posterolaterally the vagus nerve.
Medially:- The larynx, the pharynx, trachea, esophagus and lobes of thyroid gland.
Laterally:- Internal jugular vein.
The carotid body:-
Is a small gland-like structure located in the deep surface of the bifurcation of common carotid artery, it has a chemo-receptors which responds to either decrease oxygen tension or increased carbon dioxide tension in the blood which produce appropriates reflex changes in respiration.
The carotid sinus:-
Slight dilatation of the upper part of common carotid artery and the adjacent part of internal carotid artery, it has pressure receptors so distention of the wall lead to decrease in the heart rates and so decrease in blood pressure.
Both carotid body and sinus are innervated principally by glossopharyngeal nerve through the carotid sinus nerve, but they are also supplied by vagus nerve and sympathetic.
The external carotid artery:-
It begins at the upper border of thyroid cartilage as one of the terminal branches of common carotid artery, it ends behind the neck of mandible deep in the substance of the parotid gland by dividing into superficial temporal and maxillary arteries. The external carotid artery lies at first medial to internal carotid artery but then ascends laterally, it is crossed by posterior belly of digastric and stylohyoid muscles. It is one of the main artery which supplies the scalp, face, maxilla, tongue and neck.
Relation of external carotid artery:-
Anterolaterally:- At its beginnings it is overlapped by anterior border of sternocleidomastoid muscle, above it becomes superficial and covered by skin and fascia, it is crossed by posterior belly of digastric and stylohyoid muscle. Also it is crossed by the hypoglossal nerve and within the parotid gland it is crossed by facial nerve. The internal jugular vein lies lateral then posterior to external carotid artery.
Posteromedially:- Related to the wall of the pharynx and internal carotid artery. the styloid process, stylopharyngeus muscle, styloglossus muscle, glossopharyngeal nerve and pharyngeal branches of vagus nerve lies between external and internal carotid artery.
Branches of external carotid artery:-
Superior thyroid artery.
Ascending pharyngeal artery.
Lingual artery.
Facial artery.
Occipital artery.
Posterior auricular artery.
Superficial temporal and maxillary artery.
Superior thyroid artery:- arises from anterior surface of external carotid artery close to its origin, it runs anteroinferiorly to the apex of lobe of thyroid gland where it is divided into anterior and posterior branch.
Branches of superior thyroid artery:-
Infrahyoid branches.
Sternocleidomastoid branch.
Cricothyroid branch.
Muscular branches.
Superior laryngeal branch:- it is the larger branch of superior thyroid artery, it enters the larynx with the internal laryngeal nerve (branch of superior laryngeal nerve) by piercing the thyrohyoid membrane, it supplies the upper part of the larynx and adjacent pharynx.
Ascending pharyngeal artery:- this is the 1st or 2nd smallest branch of external carotid artery, ascends on the pharynx medial to the carotid arteries.
Lingual artery:- arises opposite to the tip of greater horn of hyoid bone, it disappears under hyoglossus muscle. It crossed by hypoglossal nerve.
Facial artery:- it arises above the lingual artery passes upward deep to posterior belly of digastric and stylohyoid muscle.
Occipital artery:- arises from the posterior aspect of external carotid artery opposite to facial artery. it runs along the lower border of posterior belly of digastric undercover of sternocliedomastiod muscle, it passes upward and backward to the occipital groove medial to mastoid notch.
Posterior auricular artery:- arises from posterior border of external carotid artery at the superior border of posterior belly of digastric.
Both superficial temporal artery and maxillary artery are terminal branches of external carotid artery arise behind the neck of mandible.
Internal carotid artery:-
it begins at the upper border of thyroid cartilage as one of the terminal branches of common carotid artery. it enters the cranial cavity through the carotid canal, it supplies the brain, forehead, eye and part of the nose. It has no branches in the neck.
Relation of internal carotid artery:-
Anterolaterally:- below digastric it is related to skin, fascia, anterior border of sternocleidomastoid muscle and hypoglossal nerve. Above digastric it is related to stylohyoid, stylopharyngeus muscle, glossopharyngeal nerve, pharyngeal branches of vagus nerve, parotid gland and external carotid artery.
Posteriorly:- sympathetic trunk, longus capitis muscle and transverse process of the upper three cervical vertebrae.
Medially:- pharyngeal wall and superior laryngeal nerve.
Laterally:- internal jugular vein and vagus nerve.
Internal jugular vein:-
Begins at the jugular foramen as a direct continuation of sigmoid sinus, it descends through the carotid sheath with the common carotid artery and the vagus nerve. It unites with subclavian vein to form the brachiocephalic vein behind the sternal end of clavicle. It has a superior and inferior dilatation, the deep cervical lymph nodes lies along its side. Above the vein lies posteromedial to the artery then becomes lateral to it, at the root of the neck the vein lies anterior to the common carotid artery.
Tributaries:-
Inferior petrosal sinus.
Pharyngeal plexus of vein.
Facial vein.
Lingual vein.
Superior thyroid vein.
Middle thyroid vein.
Occasionally the occipital vein.