Noninvasive Radiologic Diagnosis of Extracranial Vascular Pathologies

By Fridon Todua and Dudana Gachechiladze

This book is a state of the art guide to the diagnosis of extracranial vascular pathologies with modern noninvasive neuroimaging and vascular imaging techniques. The opening sections provide a thorough introduction to arterial and venous anatomy, basic hemodynamics, and the principles of noninvasive vascular diagnostics, including by means of color Doppler ultrasound, CT and CT angiography (356- and 640-slice systems), and MRI and MR angiography (1.5 and 3 T). The main body of the book is devoted to the use of these methods to image cerebral ischemia and a wide variety of extracranial arterial and venous anomalies and pathologies. Neuroimaging and vascular imaging diagnostic criteria are clearly identified with the aid of many high-quality images, and the advantages and disadvantages of each modality for each pathology are explained. Information is also presented on etiology, pathophysiology, and other relevant aspects. A concluding section discusses the role of complementary noninvasive functional tests. The book will be a valuable resource for neurologists, angiologists, neuroradiologists, neurosurgeons, trainees, and all physicians who care for patients with cerebrovascular diseases.

• Language: English
• Publisher: Springer
• Release date: Aug 9, 2018
• ISBN: 9783319913674

Book preview

Part IVascular Anatomy and Basic Hemodynamics

© Springer International Publishing AG, part of Springer Nature 2018

Fridon Todua and Dudana GachechiladzeNoninvasive Radiologic Diagnosis of Extracranial Vascular Pathologieshttps://doi.org/10.1007/978-3-319-91367-4_1

1. Anatomy of Cerebral Circulation System

Fridon Todua¹   and Dudana Gachechiladze², ³

(1)

Department of Radiology, National Academy of Sciences of Georgia, Research Institute of Clinical Medicine, I. Javakhishili Tbilisi State University, Tbilisi, Georgia

(2)

Department of Radiology, Programme of Caucasus University, Tbilisi, Georgia

(3)

Department of Ultrasound Diagnostics, National Medical Academy of Georgia, Research Institute of Clinical Medicine, Tbilisi, Georgia

Deceased

✠ Fridon Todua was deceased at the time of publication.

Cerebral circulation starts from aortic arch vessels (see the diagram in Fig. 1.1). The first artery coming out of the aortic arch is brachiocephalic trunk (TrB), which then divides into right subclavian and right common carotid arteries (CCA). The other branches are left subclavian and left common carotid arteries. The left CCA originates directly from the aortic arch.

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Fig. 1.1

Anatomical overview of the extracranial arteries. 1. common carotid artery; 2. external carotid artery; 3. internal carotid artery; 4. superior thyroid artery; 5. lingual artery; 6. facial artery; 7. occipital artery; 8. superficial temporal artery; 9. vertebral artery; 10. thyrocervical trunk; 11. costocervical trunk; 12. descending scapular artery; 13. internal thoracic artery; 14. subclavian artery

The cervical section of both common carotids follows a similar course. Each vessel passes obliquely upward from behind the sternoclavicular joint to the level of the upper border of the thyroid cartilage. In the lower neck, the two common carotid arteries are separated from each other by the trachea. The left CCA is usually longer than the right CCA. Common carotid arteries proceed to the brain and most often at the upper level of thyroid cartilage (at the third or fourth cervical vertebrae) divide into internal carotid arteries (ICA) and external carotid arteries (ECA). The carotid bifurcation (CB) is an anatomically and surgically important landmark as it is involved in a variety of physiological and pathological processes. The height of the carotid bifurcation is classically defined in relation with vertebral levels and is highly variable across literature. Finally, geometry of CB is a determinant of local blood hemodynamic and wall shear stress, commencing or promoting the process of atherogenesis (Uflacker 2007).

External carotid artery (ECA) provides approximately 1/3 of the blood flow supplied by common carotid artery; ECA also originates symmetrically on the both side, has a relatively short trunk, and divides into several branches (the superior thyroid artery, the lingual artery, the facial artery, the maxillary artery, the occipital and superficial temporal artery, etc.). The first large branch, superior thyroid artery, is easy detectable on ultrasound examination and can be used for differentiation between ECA and ICA.

At the carotid bifurcation, the CCA widens, and the dilatation continues into the proximal portion of the ICA. This part is called the carotid sinus. Beyond the carotid sinus, the caliber of the ICA is uniform. In this segment the arterial wall has a number of particularities: Medial layer is relatively thin and adventitia is thick, with multiple elastic fibers and baro- and chemoreceptors.

The carotid sinus contains baroceptors able to detect acute changes in arterial pressure alongside chemoreceptors able to detect acute changes in arterial oxygen. Those receptors communicate with brainstem and through reflexes regulate homeostasis of these vital parameters (Valdueza et al. 2008).

Internal carotid artery (ICA) provides 2/3 of the blood flow supplied by CCA. Its diameter is larger than of ECA. The right and left ICAs develop symmetrically and have lateral or dorsolateral position in relation to the ECA. ICA rises to the scull base without branching.

The ICA has three main segments: cervical, petrous, and intracranial segments.

At the cervical segment, the ICA is almost vertical, from the origin to the carotid canal at the base of the skull. It is closely connected to the jugular vein (JV) and the vagus nerve, which is located between and behind these two vessels, forming a neurovascular bundle.

Intrapetrosal part is located in the pyramidal channel of the temporal bone. There is a vertical and a horizontal portion of the petrous segment of the ICA. In this segment it is bordered with the venous plexus.

The intracranial portion of the ICA may be divided into three segments: the precavernous segment, the cavernous segment, and the supraclinoid segments.

The ICA runs through the carotid canal to the cranial cavity and enters the cavernous sinus, where it forms the curved carotid siphon. The upper part of carotid siphon gives its first branch—ophthalmic artery (OA). After that, the internal carotid artery enters subarachnoid cavity, where it bifurcates into two main branches: middle cerebral artery (MCA) and anterior cerebral artery (ACA).

The MCA originates from the division of the ICA. The MCA has the larger caliber among the arteries of the circle of Willis. MCA is slightly curved and runs laterally (M1 segment). At the lateral cerebral fissure, it has 2–5 branches (M2 segment).

The anterior cerebral artery (ACA) rises from the anterior wall of the ICA. It runs medially (A1 segments), passing over the optic nerve and chiasm and anteriorly in the cerebral fissure (A2 segment). It is connected by the opposite ACA over the optic chiasm through the anterior communicating artery (AComA). In this segment also starts posterior communicating artery (PComA), which connects carotid and vertebrobasilar arterial systems.

Functional particularities of carotid arteries define their histological structure. CCA belongs to so-called elastic-type arteries, which corresponds to its main function—transportation of a larger volume of blood in comparison with the other arterial systems. Elastic artery is a vessel with a large number of collagen and elastin filaments in the tunica media, which gives it the ability to stretch in response to each pulse. Internal carotid artery is a muscular-elastic artery, innervated by a number of cranial, cervical, thoracal, and spinal nerves. Periarterial plexus of internal carotid artery, spreading to intracranial vessels, consists of cervical (mainly superior sympathetic) ganglia (Lasjaunias and Berenstein 1987).

The subclavian artery, like a carotid artery, on the right side emerges from the brachiocephalic trunk and on the left side directly from aortic arch. The vertebral artery (VA), in most of cases, originates at the upper posterior aspect of the first segment of the subclavian artery (SA). VA is divided into four main segments, out of which three are extracranial and one intracranial (Fig. 1.2).

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Fig. 1.2

Vertebral arteries anatomy. 1. vertebral artery; 2. thyrocervical trunk; 3. inferior thyroid artery; 4. ascending cervical artery; 5. superior cervical artery; 6. suprascapular artery; 7. internal thoracic artery

The first segment, so-called V 1 segment of vertebral artery, starts from the subclavian artery and ends before entering the costotransverse channel. Vertebral artery enters the costotransverse channel mainly at C-V-VI level or rarely at IV-V vertebral level (V2 segment). Then it proceeds vertically up to the C-II vertebral level and establishes the V 3 segment.

The fourth segment (V4) of the VA perforates the dura and runs the cranium (IV segment) anteromedially through the foramen magnum. At the posterior edge of the pons Varolii VA, join the contralateral VA forming the single basilar artery (BA). The BA is approx. 3–4 cm long. Sometimes the course of the BA is tortuous and deviated from the midline. The BA at the anterior edge of the pons Varolii divides into two posterior cerebral arteries (PCA) (Fig. 1.3).

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Fig. 1.3

Intracranial arteries and circle of Willis. 1. superior cerebellar artery; 2. basilar artery; 3. pontine branches; 4. vertebral artery; 5. anterior spinal artery; 6. posterior spinal artery; 7. anterior cerebral artery; 8. anterior communicating artery; 9. middle cerebral artery; 10. internal carotid artery; 11. posterior communicating artery; 12. posterior cerebral artery; 13. artery of labyrinth; 14. anterior and posterior cerebellar artery; I–VI cranial nerves

The PCA generally receives the supply from the BA and has a communication with the ICA through the posterior communicating artery (PComA).

Extracranial part of the vertebral artery is an elastic-type vessel, while its intracranial segment is muscular (distributing) artery. It is innervated by a number of cranial, cervical, and spinal nerves, first two thoracic nerves, and sympathetic cervical plexus.

The anterior and posterior circulation systems connect via the unpaired anterior communicating arteries (ACoA) and paired posterior communicating arteries (PComA), to form cerebral arterial system—circle of Willis. The circle of Willis is more polygonal than circular. The circle of Willis anatomically connects two carotid systems and also the anterior and posterior circulation systems. The perfect Willis’s circle is symmetric, consisting of intracranial parts of ICA, proximal parts of anterior and posterior cerebral arteries, and posterior communicating arteries (Fig. 1.3).

Owing to the lack of a valvular system, blood flow through this circle can follow the direction of need. Two parts are connected through the anterior communicating artery in the front part and through the oral segment of the basilar artery in the back part. Functionally, the circle of Willis is an anastomosis between the arterial systems and plays an important role in compensation of hemodynamic changes.

Analysis of geometrical structures of the Willis’s circle shows that typical (classical) anatomy is founded in approximately 30% of the population. The vessels of the circle of Willis vary in caliber and are often maldeveloped or even absent. Cerebral and communicating arteries, anterior and posterior, may be absent, hypoplastic, double, or triple (Riggs and Rupp 1963).

Anomalies are mostly presented in the posterior part of the circle of Willis. The most frequent anomaly is absence of posterior communicating artery (6–10% of cases), while aplasia of the anterior communicating artery occurs in 0.5–3% of cases. Posterior trifurcation of internal carotid artery (emersion of posterior cerebral artery from ipsilateral internal carotid artery) occurs in 14–25% of cases, while anterior trifurcation (emersion of both anterior cerebral arteries from a single internal carotid artery) only in 7–16% (Riggs and Rupp 1963; Hendrikse et al. 2005; Kapoor et al. 2008).

The intracranial venous circulation, assumed to be 60–70% of the global cerebral blood volume, does have an important role in the equilibrium of cerebral perfusion. Two important differences from the general venous system should be mentioned here. (1) Intracranial venous vessels do not collapse, even if the transmural pressure is zero. (2) There is complete absence of any venous valves up to the level of the internal jugular veins permitting free blood flow in any direction depending on need (Uflacker 2007).

Structural units of the cerebral venous system are postcapillary venules, cerebral veins, and venous sinuses. Blood flows from postcapillary network into the intracranial veins. The intracranial veins can be divided into deep and superficial cerebral venous systems (Fig. 1.4).

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Fig. 1.4

Anatomical overview of the cerebral veins and sinuses. Upper sinus group: 1. superior sagittal sinus; 2. inferior sagittal sinus; 3. straight sinus; 4. confluence of sinuses; 5. transverse sinus; 6. sphenoparietal sinus. Lower sinus group: 7. cavernous sinus; 8. inferior petrosal sinus; 9. sigmoid sinus; 10. superior petrosal sinus. Deep veins: 11. internal cerebral vein; 12. basal vein; 13. great cerebral vein; 14. internal jugular vein; 15. external jugular vein; 16. ophthalmic vein; 17. facial vein

Superficial venous system is draining the blood from the hemispheres. It is supplied with blood from the major part of cerebral cortex and white substance and then provides blood mainly to the sinuses of cortex. The superficial veins over both hemispheres connect to a vascular network which can be classified, according to the flow direction, into ascending and descending veins. The ascending veins take the blood into the superior sagittal sinus (SSS), transverse sinus.

The most prominent descending superficial veins are the vein of Labbé, draining into the transverse sinus (TS), and Sylvian vein, predominantly draining into the sphenoparietal sinus (SpPSs) (Fig. 1.4).

The deep venous system of the brain is located in the cerebral parenchyma and consists of groups of venous trunks, which collect blood from transparent interseptum, plexuses and walls of lateral ventricles, subcortical nodes, optic thalamus, stem, and cerebellum. Deep system is formed by the internal cerebral veins, the basal veins of Rosenthal (BVR), and the thalamic veins. The site of drainage of this system is the great vein of Galen (VG) and the straight sinus (StS). The BVR usually drain posteriorly into VG. The VG mergers with a number of small profound veins and ten communicate to the StS, which is the main deep collector of venous blood.

Superficial and deep venous systems are closely connected both through direct venous anastomoses and anastomoses of venous sinuses. Major part of blood from superficial and deep venous systems (2/3) flows into internal jugular vein through sinuses and 1/3 of this blood into external jugular vein through pericranial anastomoses (Sellar 1995).

The venous sinuses are the final recipients of the blood. Contrary to other intracranial veins, they cannot change their diameter as they are surrounded by an inflexible dural sheath. They then take the blood via the sigmoid sinus (SiS) to the IJV. Besides the CoS the paired cavernous sinuses (CS) are another major blood collector distributor. It drains blood from the orbit and from the Sylvian veins mainly via the SpPS. From there blood can be drained via the inferior petrosal sinus (IPS) or superior petrosal sinus (SPS) into the IJV.

The external jugular vein drains mainly the scalp and face but also some deeper tissues. External jugular vein starts at the level of lower jaw angle, under the ear auricle, and then descends along the lateral surface of musculus sterno-cleido-mastoideus.

The internal jugular vein (JV) drains most of the blood from the skull, brain, and superficial and deep parts of the face and neck. It originates at the jugular foramen at the cranial base, in continuation with the sigmoid sinus. The vein is dilated at the beginning and is called the superior bulb. Behind the sterno-cleido-mastoideal muscle, the jugular vein connects with subclavian vein, and they both create the right and left brachiocephalic veins, the union of which then forms the vena cava superior.

The vertebral vein is formed from numerous small tributaries from the internal vertebral plexus, which arise from the vertebral canal above the posterior arch of the atlas. It runs together with the VA through the costotransverse foramina of the two-sixth cervical vertebrae and opens in the subclavian vein.

Based on a number of large-scale multicenter studies, a consensus was established on the indication to the examination of extra- and intracranial vessels, according to which examination of extracranial arteries is indicated in case of the following conditions: clinical signs of cerebrovascular insufficiency, headache, and high risk of cerebrovascular diseases (smoking, hyperlipidemia, obesity, arterial hypertension, diabetes mellitus, injury of other arterial systems—especially acute coronary syndrome, atherostenosis of lower limb vessels). Examination of intracranial arteries is indicated in case of the following conditions: cerebral circulatory disorders caused by the established stenosis or occlusive processes of extracranial arteries, indirect signs of damage to intracranial arteries, and signs of acute or chronic cerebral ischemia without the known reason; Changes in cerebral parenchyma established by neuroimaging (computer or magnetic resonance tomography).

Examination of extra- and intracranial veins is indicated in case of stenosis or occlusive processes in the arterial or venous systems, for the purpose of studying their structure and assessment of permeability and embolic hazard of vessels, in case of deformations, anomalies, arterial and venous aneurisms, arterial and venous malformations, and vasospasm.

References

Hendrikse J, Van Raamt AF, Van der Graaf Y et al (2005) Distribution of cerebral blood flow in the circle of Willis. Radiology 235:184–189Crossref

Kapoor K, Singh B, Dewan LI (2008) Variations in the configuration of the circle of Willis. Anat Sci Int 83:96–106Crossref

Lasjaunias P, Berenstein A (1987) Surgical neuroangiography – 1 functional anatomy of craniofacial arteries. Springer, New York, pp 1–426

Riggs HE, Rupp C (1963) Variation in form of circle of Willis. The relation of the variations to collateral circulation: anatomic analysis. Arch Neurol 8:24–30Crossref

Sellar RJ (1995) Imaging blood vessels of the head and neck. J Neurol Neurosurg Psychiatry 59(3):225–237Crossref

Uflacker R (2007) Atlas of vascular anatomy: an angiographic approach, 2nd edn. Lippincott Williams & Wilkins, Philadelphia

Valdueza J, Schreiber S, Roehl JE, Klingebiel R (2008) Neurosonology and neuroimaging of stroke. Thieme, New York 383pp

© Springer International Publishing AG, part of Springer Nature 2018

Fridon Todua and Dudana GachechiladzeNoninvasive Radiologic Diagnosis of Extracranial Vascular Pathologieshttps://doi.org/10.1007/978-3-319-91367-4_2

2. Basic Principles of Hemodynamics

Fridon Todua¹   and Dudana Gachechiladze², ³

(1)

Department of Radiology, National Academy of Sciences of Georgia, Research Institute of Clinical Medicine, I. Javakhishili Tbilisi State University, Tbilisi, Georgia

(2)

Department of Radiology, Programme of Caucasus University, Tbilisi, Georgia

(3)

Department of Ultrasound Diagnostics, National Medical Academy of Georgia, Research Institute of Clinical Medicine, Tbilisi, Georgia

Deceased

✠ Fridon Todua was deceased at the time of publication.

Just as hydrodynamics describe the motion of fluids, especially ideal liquid-water, and the interaction of the fluid with its boundaries, hemodynamics studies flow characteristics of blood and its interaction with the walls of the vessels and different obstacles in their lumen. The underlying principles of fluid mechanics applied to the flow of blood are a complex subject, which is discussed in detail in a number of tests including those by Strakee and Westerhof (1993), Wolf and Fobbe (1995), and Allan et al. (2000).

In its journey from the heart to the tissues, the blood passes through vessels of six principal types: elastic arteries, muscular arteries, arterioles, capillaries, venules, and veins. In this system, the arteries show a progressive reduction in diameter as they recede from the heart, from about 25 mm in the aorta to 0.3 mm in some arterioles. The reverse is true for the veins; the diameter is small in the venules and progressively increases as the veins approach the heart. All arteries are comprised of three distinct layers, intima, media, and adventitia, but the proportion and structure of each vary with the size and function of the particular artery.

Elastic arteries are aorta and pulmonary artery, as well as proximal segments of magistral arteries; elastic-muscular are large-caliber arteries (carotid, subclavian, pelvic, femoral, and other arteries). Elastic arteries have the thickest walls, containing a high percentage of elastic fibers in all three of their tunics. A big amount of elastic fibers enables them to maximally dilate during the systole and return to the initial condition during the diastole. Their function is to transport blood in permanent flow and amortize systolic pulse wave. An elastic artery is also known as a conducting artery, because the large diameter of the lumen enables it to accept a large volume of blood from the heart and conduct it to smaller branches.

Farther from the heart, in relatively low-caliber vessels, where the surge of blood has dampened, the percentage of elastic fibers in an artery’s tunica intima decreases and the amount of smooth muscle in its tunica media increases. The artery at this point is described as a muscular artery. Their thick tunica media allows muscular arteries to play a leading role in vasoconstriction. In contrast, their decreased quantity of elastic fibers limits their ability to expand. Fortunately, because the blood pressure has eased by the time it reaches these more distant vessels, elasticity has become less important. As it proceeds distally, one structural type of artery gradually transforms into the other.

Precapillary vessels (end arteries and arterioles) are of a relatively small diameter and at the same time have walls with a well-developed smooth muscle layer. Arterioles have the same three tunics as the larger vessels, but the thickness of each is greatly diminished. The critical endothelial lining of the tunica intima is intact. The tunica media is restricted to one or two smooth muscle cell layers in thickness. The tunica externa remains but is very thin. Due to their structure, they greatly contribute to the peripheral resistance. Activity of muscle fibers causes changes in the diameter of vessels and, hence, in the traverse section of arteries. Given that hemodynamic resistance is directly dependent upon the diameter of the vessel, the role of these vessels in regulating the volume flow rate and microcirculation mode becomes obvious. Activity of the sphincteric precapillary arterioles determines the number of functioning capillaries and, hence, the size of their metabolic surface.

Exchange of gases and other substances occurs in the capillaries between the blood and the surrounding cells and their tissue fluid (interstitial fluid). Flow through capillaries is often described as microcirculation.

Capillaries have no traction ability. Their diameter changes passively, following the change of pressure in pre- and postcapillary resistance arteries and sphincters. While diffusion and filtration also take place in venules, the later also belong to metabolic vessels.

Additionally, an arteriovenous anastomosis may bypass the capillary bed and lead directly to the venous system.

Volumetric vessels include veins. Due to their passive extending capacity, veins have a role of a reservoir. According to the muscle elements in their walls, veins can be of muscle type and tissue type (without muscle elements). Tissue veins are those of the dura mater and pia mater, retina, bones, spleen, and placenta. All these veins are adhered to hard structures of corresponding organs and do not deflate.

A venule is an extremely small vein, generally 8–100 μm in diameter. Multiple venules join to form veins. The walls of venules consist of endothelium, a thin middle layer with a few muscle cells and elastic fibers, plus an outer layer of connective tissue fibers that constitute a very thin tunica externa. Venules as well as capillaries are the primary sites of emigration or diapedesis.

Veins conduct blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens. Because they are low-pressure vessels, larger veins are commonly equipped with valves that promote the unidirectional flow of blood toward the heart and prevent backflow toward the capillaries caused by the