Carotids

Generality

The carotids are two large arterial vessels in the neck, the branches of which supply the central nervous system and facial structures.

We distinguish, respectively, a "right carotid artery and a" left carotid artery. Like the vertebral arteries, they have the function of carrying blood to the brain. In addition to oxygenating the cerebral districts, the carotid arterial system also supplies the areas of the head corresponding to the face and eyes. The most common pathologies that compromise the functionality of the carotids are arteriosclerosis and atherosclerosis.

• Arteriosclerosis causes a loss of elasticity and contractility, as well as a modification of the vessel size.
• Atherosclerosis determines the formation of plaques (atheromas) which occlude the lumen of the arterial vessel.

Anatomical references to the arteries

Arteries are vessels that originate directly or indirectly from the heart and, receiving oxygenated blood from the latter, supply all tissues and organs of the human body. The blood in the arteries flows in a centrifugal direction, ie towards the periphery.

As one distances oneself from the heart, the arterial system gradually branches out. Therefore, the caliber of the vessels is reduced; in this regard, we can distinguish:

• Large caliber vessels, whose diameter measures at least 7 mm. They are the arteries that originate from the heart, such as the aorta or the carotids themselves
• Medium-sized vessels, whose diameter measures between 7 mm and 2.5 mm.
• Small caliber pots, the diameter of which measures less than 2.5 mm.
• Arterioles, the last branches of the arterial system. They measure less than 100 microns.

As for the veins, the wall of the arteries is also made up of 3 concentric layers, of variable thickness and structure depending on the size of the vessel. The 3 layers are:

• The intimate cassock, lined with endothelium. It is the innermost part of the vase.
• The medium tunic, made up of elastic and muscular fibers. The elastic component prevails in the great vessels; while the muscular component prevails in medium caliber vessels
• The adventitious tunic, made up of connective tissue and, sometimes, of muscle and elastic fibers. It is the outermost part of the vase.

Anatomy of the carotid arteries

The carotids are classified as large-caliber arteries, as they originate from the heart. They spray the following districts or areas of the head:

• Brain.
• Face.
• Eyes.

There are two carotid arteries, right and left, and each has two terminal branches, called the external carotid artery and the internal carotid artery. Therefore, the carotid arterial system can be schematized as follows:

• Two common carotid arteries, right and left.
• Two branches for a single common carotid:
  • the external carotid
  • the internal carotid.

The right common carotid arises from the anonymous, or brachycephalic, right aorta, one of the first vessels that arise from the arch of the aorta. The left common carotid, on the other hand, originates directly from the "arch of the aorta". Their length, of course, is different: the right is shorter.
The two vessels, right and left, are directed upwards and terminate about one centimeter above the upper portion of cartilage that makes up the thyroid. Here they are each divided into two branches, the external carotid artery and the internal carotid artery. .

Originating directly from the aortic arch, the left carotid artery establishes relationships with other parts of the body, adjacent to it, at the endothoracic level. It relates to:

• The anonymous vein on the left, in front.
• The trachea and the esophagus, behind.
• The left vagus nerve, laterally.

In the neck, the two common carotids, right and left, contract the same relationships with neighboring organs. They contact:

• The internal jugular vein and with the vagus nerve of each side. All together, they form the neurovascular bundle of the neck.
• Pharynx, esophagus, larynx, trachea, thyroid gland and nerves are the relationships at the medial level.

The external carotid artery crosses various muscles (digastric and stylohyoid), venous vessels (tirolinguofacial) and nerves (hypoglossal) of the head, reaching the parotid gland.
Proceeding from bottom to top, the external carotid artery emits the following collateral branches:

• Superior thyroid artery.
• Lingual artery.
• Sternocleidomastoid artery.
• External maxillary artery.
• Occipital artery.
• Pharyngomeningeal artery.
• Posterior auricular artery.
• Parotid arteries.

Finally, it ends at the level of the mandible. Here it branches into:

• Superficial temporal artery.
• Internal maxillary artery.

The internal carotid artery, on the other hand, ends inside the skull. It too contracts relationships with the muscles, venous vessels and nerves of the head. It has numerous relationships, the main ones established with:

• The digastric, stylohyoid, pharyngeal and stiloglossal muscles
• The internal jugular vein
• Vagus nerve, glossopharyngeal nerve and hypoglossal nerve.

The internal carotid artery, at its terminal point, perforates the dura mater and penetrates the endocranium (the internal wall of the skull). In this area, it makes contact with various nerves of the eye.
The collateral ramifications are as follows:

• Caroticotympanic artery
• Ophthalmic artery
• Middle cerebral artery
• Anterior chorionic artery
• Posterior communicating artery.

The terminal branch, on the other hand, is the anterior cerebral artery.

Pathologies

The most common pathology affecting the carotid system is arteriosclerosis. It is a typical disease of the arteries and has the following characteristics:

• Increase in consistency, followed by tissue hardening of the vessel wall. In this case we speak of sclerosis.
• Modified vessel thickness: thickening or thinning.
• Changed vessel length: the artery lengthens and becomes more tortuous.
• Modified internal surface: becomes irregular.
• Modified caliber: dilation or stenosis of the vessel.

These characteristics determine two typical consequences of arteriosclerosis:

• Decreased vascular elasticity.
• Decreased vascular contractility.

The circulation through the atherosclerotic vessels is therefore insufficient and generates serious complications in inadequately oxygenated tissues. This is what happens to the carotid system: the cerebral districts, the face and the eyes lose their normal capacity. The effects, unfortunately, they are not limited to these sites: in fact, there is also a loss of control of the limbs innervated by the areas of the brain no longer reached by a correct blood flow.

Among the forms of atherosclerosis, various pathologies with particular clinical pictures are included. One of these is atherosclerosis. The other pathological forms affect arteries of medium and small caliber, therefore, this is not the right place to talk about it.
Atherosclerosis is a disease typical of the most elastic arteries present in the human body: therefore, it preferably affects large-caliber arterial vessels, which originate from the heart; secondly, it also affects the medium-sized vessels that originate from arteries with higher caliber.
Atherosclerosis has the following general characteristics:

• The medium tunic (in the innermost layers), and, above all, the intimate tunic are characterized by the presence of focal plates, forming reliefs and made up of fibrolipidic material. These plaques are called atheromas. Their distribution is therefore well localized.
• The fibrolipid consistency of atheromas is a consequence of an accumulation of lipid material and the proliferation of the fibrous component of the connective tissue.
• Atheromas can be distributed as foci, but never as continuous structures that affect the arterial vessel: the atherosclerotic artery always presents undamaged areas.
• It has a slow and progressive evolution over time.
• It affects every individual, with greater incidence in the male. The first atherosclerosis processes can develop as early as the 2nd or 3rd decade of life. Around the 6th decade of life, atheromatous lesions are common and evident.
• It can be asymptomatic.
• Complications: myocardial infarction, intestinal infarction, cerebral hemorrhage, aneurysms and senile gangrene of the lower extremities.

In the carotids, the atheromatous plaques are distributed in a variable way and often become the site of thrombotic deposits, obstructing the lumen. This pathological situation is known with the term carotid stenosis.
Finally, other pathologies affecting the carotid artery are due to trauma, aneurysms and thrombangiitis obliterans.