Cerebral Venous Circulatory System Evaluation by Ultrasonography

Acta Clin Croat 2013; 52:203-211 Review

CEREBRAL VENOUS CIRCULATORY SYSTEM EVALUATION BY ULTRASONOGRAPHY

Iris Zavoreo1, Vanja Bašić-Kes1, Lucija Zadro-Matovina1, Marijana Lisak1, Lejla Ćorić1, Timon Cvjetičanin1, Dubravka Ciliga2 and Tatjana Trošt Bobić2

1University Department of Neurology, Sestre milosrdnice University Hospital Center; 2Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia

SUMMARY – Venous system can be classified as pulmonary veins, systemic veins and venous sinuses that are present only within the skull. Cerebral venous system is divided into two main parts, the superficial and the deep system. The main assignment of veins is to carry away deoxygenated blood and other maleficient materials from the tissues towards the heart. Veins have thinner walls and larger lumina than arteries. Between 60% and 70% of the total blood volume is found in veins. The major factors that influence venous function are the respiratory cycle, venous tone, the function of the right heart, gravity, and the muscle pump. Venous system, in general, can be presented by selective venography, Doppler sonography, computed tomography (CT) venography and magnetic resonance (MR) venography, and cerebral venous system can be displayed by selective venography, cerebral CT venography, cerebral MR venography, and specialized extracranial and transcranial Doppler sonography. The aim of this paper is to show the possibilities of intracranial and extracranial ultrasound evaluation of the head and neck venous circulation and chronic cerebrospinal venous insufficiency as one of the most common pathologies evaluated as part of neurodegenerative processes in the central nervous system. Key words: Veins – radiography; Veins – ultrasonography; Cerebral veins – ultrasonography; Cerebro- vascular disorders; Chronic cerebrospinal venous insufficiency; Transcranial doppler sonography; Zamboni protocol

Introduction to maintain body homeostasis. Neurodegenerative disorders are usually connected with insufficient The main components of the human cardiovascu- arterial circulation, but in the underlying physiopa- lar system are heart, blood and blood vessels. Blood thology venous circulation should also be evaluated. vessel system consists of a large network of arteries, Nowadays, ultrasound is a well established tool in arterioles, capillaries, venules and veins. The main the evaluation of the arterial part of cerebral circula- assignment of arteries is to deliver oxygen and nu- tion, while venous circulation and its role in brain trients to all parts of the body, while the main as- metabolism has been forgotten. In the last few years, signment of veins is to remove carbon dioxide and the term chronic cerebrospinal venous insufficiency maleficent materials from cells and tissues in order (CCSVI) has been used for disturbances of the morphology and flow in the head and neck venous circulation. This term is mostly used in new theories on Correspondence to: Assist. Prof. Iris Zavoreo, MD, PhD, Universi- the pathophysiology of multiple sclerosis and other ty Department of Neurology, Sestre milosrdnice University Hos- pital Center, Vinogradska c. 29, HR-10000 Zagreb, Croatia neurodegenerative disorders. Therefore, radiologic E-mail: [email protected] as well as ultrasound criteria for CCSVI have been Received April 16, 2012, accepted May 23, 2013 established.

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Human Circulatory System is lined with endothelial cells that constitute the third layer called tunica intima. Some veins have valves Arterioles extend and branch out from an artery that prevent the reflux of blood and aid in the return and lead to capillaries. Capillaries as the smallest of of blood against gravity. These valves are formed by a body’s blood vessels enable the exchange of water, folds of the innermost layer of the vein, tunica interna, oxygen, carbon dioxide and other nutrients and ma- into the lumen1. Because of their thin walls and larger leficent chemical substances between blood and sur- lumina, veins act as low-resistance blood reservoirs. rounding tissues. Venules are blood vessels that drain Between 60% and 70% of the total blood volume is blood directly from the capillary beds and unite to found in veins. Consequently, veins are also called form a vein. The main assignment of veins is to carry “capacitance vessels”2. away deoxygenated blood and other maleficent materials from the tissues towards the heart except for Cerebral venous system morphology the pulmonary venous system that brings oxygenated Cerebral venous system can be divided into two blood from the pulmonary circulation back to the left 3-5 atrium of the heart. Although most veins take blood basic components, a superficial and a deep system . back to the heart, there is also an exception. Portal The superficial system comprises of sagittal sinuses veins carry blood between capillary beds. and cortical veins and these drain superficial surfaces of both cerebral hemispheres. The superficial cerebral veins can be divided into three collecting systems, Venous System Classification the first draining into the superior sagittal sinus and Venous system can be classified as pulmonary straight sinus, the second draining into the lateral si- veins, systemic veins and venous sinuses that are pres- nus, and the third draining into the cavernous sinus. ent only within the skull. Systemic veins whose course The superior sagittal sinus and straight sinus drain a is close to the surface of the skin and have no cor- major part of the cerebral hemispheres. The lateral responding arteries are superficial (cutaneous) veins. sinuses receive blood from the cerebellum, the brain They channel blood from cutaneous tissues to deep stem and posterior parts of the hemisphere. The cav- veins via perforations in the deep fascia. Systemic ernous sinuses drain blood from the orbits, the infe- veins situated deeper in the body and having corre- rior parts of the frontal and parietal lobe, and from sponding arteries are deep veins. Most of the deep the superior and inferior petrosal sinuses. Blood from 6 veins share routes with the arteries, and many of them them flows into the internal jugular veins (IJV) . are enclosed in the same sheaths. The precise location The deep system comprises of lateral sinus, straight of veins is much more variable from person to person sinus and sigmoid sinus along with draining deeper than that of arteries1,2. cortical veins. In summary, blood from the deep white matter of the cerebral hemisphere and from the basal ganglia is drained by internal cerebral veins and basal Venous System Morphology veins of Rosenthal, which join to form the great vein Veins have thinner walls and larger lumina than of Galen that drains into the straight sinus7. arteries. Their walls consist of three layers. The outer- Both systems, deep and superficial, mostly drain most layer, called tunica externa or tunica adventitia, themselves into the IJVs. The cerebral veins and sinus- is at the same time the thickest layer on these ves- es neither have valves nor tunica muscularis. Because sels. It is composed of networks of elastic and collagen they lack valves, blood flow is possible in different -di fibers, i.e. the connective tissue. Middle-layer, called rections. Moreover, the cortical veins are linked by nu- tunica media, consists of bands of smooth muscle merous anastamoses, allowing for the development of which are, in general, thin, as veins do not function a collateral circulation. The lack of tunica muscularis primarily in a contractile manner. Comparing veins permits veins to remain dilated. Venous sinuses are to arteries, veins possess a thinner tunica media, with located between two rigid layers of dura mater8. This little smooth muscle and elastic fibers, and are there- prevents their compression when intracranial pressure fore more distensible. The interior of the venous wall rises. The dural sinuses, especially the superior sagittal

204 Acta Clin Croat, Vol. 52, No. 2, 2013 Iris Zavoreo et al. Ultrasound of brain venous circulation sinus, contain most of the arachnoid villi and granula- collapse; consequently, they reach subatmospheric tions, in which absorption of the cerebrospinal fluid pressures (<0 mm Hg). takes place9. Muscle contraction facilitates VR by compressing veins. The contractions and relaxation of the muscles surrounding deep veins help push blood upwards. Venous System Physiology The effect known as the muscle pump accomplish Venous return (VR) is the volume of blood that the valves that prevent the blood reflux back into the reaches the right heart. Many factors and variables af- lower limb, thereby assisting the unidirectional flow 2,3,10 fect VR. If these variables are kept constant, however, of blood into the right atrium . VR is inversely proportional to the central venous pressure. Also, in hemodynamically stable conditions, Venous System Imaging Methods VR is roughly equal to cardiac output. The major factors that influence VR are the respiratory cycle, ve- Venous system, generally, can be presented by se- nous tone, the function of the right heart, gravity, and lective venography, Doppler sonography, computed the muscle pump10. tomography (CT) venography (CTV) and magnetic During the respiratory cycle, due to the negative in- resonance (MR) venography (MRV). Cerebral venous trathoracic pressure during inspiration, central venous system can be displayed by selective venography, cere- pressure decreases, thereby increasing VR. Negative bral CTV, cerebral MRV, and specialized extracranial intrathoracic pressure is transmitted to the great tho- and transcranial Doppler sonography. racic veins, and as the diaphragm moves downward, Selective venography is an invasive procedure in which the venogram is taken only after a special dye the intra-abdominal pressure increases, thereby help- has been injected via a catheter into the vein. ing move blood toward the heart. When intrathoracic CTV reliably reveals all cerebral veins and sinuses pressure increases, these mechanisms are reversed. when they are seen with MR. Cerebral CTV is supe- Venous tone affects VR by modifying the capaci- rior to MRV in the identification of cerebral veins and tance of veins and is primarily regulated by the auto- dural sinuses and is at least equivalent in the diagno- nomic system. sis of dural sinus thrombosis venography. In addition, From the right ventricle, the blood is pumped out CTV more frequently visualizes sinuses or smaller into the pulmonary circulation. When the ventricle cerebral veins with low flow as compared with MRV. contracts, it moves down and pushes blood out, and The high-flow draining veins of cerebral and dural -ar because the great vessels hold the heart in place, a teriovenous malformations, vein of Galen malforma- mechanism of “cardiac suction” ensues, drawing blood tion and carotid cavernous fistula are better seen on into the atria. As blood fills the atria, the atrial walls 2,3 contrast-enhanced three-dimensional gradient-echo stretch and atrial pressure decreases . 20 MRV . Gravity affects VR by establishing a gradient be- Venous system can also be presented by using spe- tween the intrathoracic venous compartment and the cialized extracranial and transcranial Doppler sonog- lower or dependent extremities. For each centimeter 11,13 raphy . CCSVI was first found using these meth- below the right atrium, venous pressure increases by ods. about 0.75-0.8 mm Hg. The effect of gravity on venous pressure is such that it causes blood pooling in Chronic Cerebrospinal Venous Insufficiency the legs, and if a person stands quietly for a prolonged period, fainting may occur despite compensatory Chronic cerebrospinal venous insufficiency (CCS- mechanisms. This effect is due to a reduction in the VI) describes compromised blood flow in the veins perfusion pressure of the brain. Venous pressure above draining the central nervous system. It is hypoth- the right atrium decreases in the upright position. The esized that it plays a role in the cause of multiple scle- 11-14 pressure in the neck veins is close to 0 mm Hg, and rosis (MS) . Zamboni et al. claimed that in MS pa- this low pressure causes them to collapse. However, tients diagnosed with CCSVI, the azygos and IJV are the dural sinuses have rigid walls that prevent their stenotic in around 90% of cases. They theorize that

Acta Clin Croat, Vol. 52, No. 2, 2013 205 Iris Zavoreo et al. Ultrasound of brain venous circulation malformed blood vessels cause increased deposition of Neurovascular Disease held a meeting in Bologna in iron in the brain, which in turn triggers autoimmunity March 2011, where experts discussed the techniques and degeneration of the nerve myelin sheath11. Most and criteria for CCSVI. There was a consensus opin- of the venous problems in MS patients have been re- ion that intracranial and extracranial venous circula- ported to be truncular venous malformations, includ- tion can be evaluated by any vascular ultrasound ma- ing azygous stenosis, defective jugular valves and jug- chine through standard transtemporal approach or ular vein aneurysms. Problems with the innominate pterygoidal approach, as suggested by Zamboni et al.; vein and superior vena cava have also been reported the specially created Quality Doppler Profile (QDP) to contribute to CCSVI14. The proposed consequenc- available on Esaote-Biosound machines is helpful in 11,23 es of CCSVI syndrome include intracranial hypoxia, the evaluation of CCSVI, but it is mandatory . delayed perfusion, reduced drainage of catabolites, Each subject has to be investigated first in supine increased transmural pressure15-17, and iron deposits position and then in sitting position (with tilt chair around cerebral veins18,19. Multiple sclerosis and other if possible), to detect the following five parameters of 25 neurodegenerative diseases have been proposed as an the Zamboni protocol : outcome of CCSVI. Iron is needed by all living be- 1. Reflux in the internal jugular veins (IJVs) and/or ings. In addition to maintaining cellular balance and vertebral veins (VVs) in sitting and supine posture enabling nerve cells to perform routine functions, iron (Figs. 1 and 2a, 2b). forms tissues and blood vessels; it transports oxygen 2. Reflux in the intracranial veins. Reflux is defined through the body via blood circulation; it enables as a reversal of flow direction during the inspira- nerve impulses to be transmitted; and it is essential tory and expiratory phase during normal breathing to the development of myelin and oligodendrocytes with mouth closed. The transcranial color-coded (which produce and maintain healthy myelin). Iron is duplex sonography (TCCD) studies were carried deposited in varying amounts in different cells within out using one of two different approaches: the the body, according to their specific need for proper classic transtemporal window or the transcondylar functioning. While the benefits of iron in normal window (Figs. 3 and 4). levels are clear, and even critical for bodily function, 3. B-mode evidence of abnormalities in the IJVs, conversely, too much stored iron can cause problems. such as stenoses, malformed valve, annulus, septa, For instance, as people age, iron is more likely to ac- etc. (Fig. 5). cumulate in the brain. Conditions such as Alzheimer’s disease and Parkinson’s disease can also occur in con- 4. Flow not Doppler-detectable in IJVs and/or VVs nection with iron stores20. despite numerous deep breaths (Fig. 6). A randomized controlled study in 499 patients 5. Reverted postural control of the main cerebral ve- confirmed the prevalence of CCSVI in MS patients nous outflow pathways, detected by measuring the that was twice as high as in healthy controls, but this difference in IJV cross-sectional area (CSA) between prevalence was also increased, to a lesser extent, in the supine and upright positions (Fig. 7a, 7b). 21 patients with other neurologic diseases . If there is a Two of the criteria are considered sufficient for the relationship between CCSVI and MS, it is expected diagnosis of CCSVI11,13,24,25. 22-24 to be a complex one . Further investigations are Venous hemodynamics insufficiency severity score undergoing. (VHISS) is an ordinal measure of the overall extent and number of venous hemodynamics (VH) flow pat- Doppler techniques for evaluation of CCSVI tern anomalies. A higher value of VHISS indicates Cerebral venous circulation can be examined using greater severity of VH flow pattern anomalies. For echo-color Doppler equipped with 2.5 and 7.5 MHz each of the five VH criteria, the “VHISS contribu- transducers. Usually, physicians evaluate intracranial tion score” can be calculated. These scores combined circulation using transtemporal window. In search gave an overall severity measure, i.e. the VHISS. The for better correlation of the results among different minimum possible VHISS value is 0 and the maxi- centers and evaluators, the International Society for mum is 16.

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 Fig. 1. Reflux (red part of the hemodynamic spectrum in internal jugular vein – blue coded vessel on the right). Red coded vessel on the left is common carotid artery.



Fig. 3. Transcranial color Doppler of venous circulation, transtemporal approach (Rosenthal vein).

  Fig. 2a. Left panel: quality Doppler profile spectrum showing retrograde flow in internal jugular vein (blue  coded; white arrow) and anterograde flow in common carotid artery (red coded; yellow arrow). Fig. 2b. Right panel: separation of the quality Doppler profile for internal jugular vein with separation of the color coded flow (white arrow); normal flow in common  carotid artery (yellow arrow).

As regards criterion VH1, there are eight venous segments that can potentially exhibit reflux in the two  postures, and one point was assigned for each one at which reflux was found to be present. VH1 had a  VHISS contribution score that could range from a minimum of 0 to a maximum of 8.

 Criterion VH2 was assigned a VHISS contribution score of 1 if reflux was present in the intracranial veins in only one posture and a VHISS contribution score of 2 if it was present in both postures. The VHISS contribution score for this criterion was ad- ditionally weighted with a factor of 2 if reflux toward

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Fig. 4. Quality Doppler profile of cerebral venous sinuses through transcondylar approach (petrosal sinuses).



Fig. 5. Left panel: lumen of the vein without any wall defects. Right panel: valve (closed position – yellow arrow). the subcortical grey matter could be detected. VHISS The scoring scheme for the contribution of VH4 contribution score for VH2 could range from a mini- to the VHISS was the same as that for VH1, with mum of 0 to a maximum of 4. the difference being that only blocks were considered. The VHISS contribution score for VH3 ranged No points were assigned for segments and postures from 0 to 2, depending on whether B-mode anomalies in which reflux had previously been detected under disturbing outflow were present in none, one or both VH1. of the IJVs, respectively. VH3 was assigned a contri- The VH5 criterion had an overall VHISS contribution score of 0 if either VH1 or VH4 was positive bution score between 0 and 4, calculated by assigning for the presence in either posture of reflux or obstruc- 0 to 2 points for each IJV. A -ΔCSA value was as- tion in the IJV of interest. signed a score of 2, whereas a ΔCSA value <7 mm2,

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Fig. 6. Absence of color flow and collapsed lumen of internal jugular vein (yellow arrow) and absence of Doppler spectra (white arrow) despite numerous deep breaths. 

 corresponding to the 25th percentile of ΔCSA distribution in healthy controls, was assigned a score of 1. ΔCSA >7 mm2 was assigned a score of 0. The overall VHISS score was defined as a weighted sum of the scores contributed by each individual abnormal venous hemodynamics criterion. It is still not clear whether MRV, venous angiography, or Doppler sonography should be considered the gold standard for the diagnosis of CCSVI21. The use of MRV for the diagnosis of CCSVI in MS patients has been proposed by some to have limited value, and should be used  only in combination with other techniques26. Others have stated that MRV has advantages over Doppler since results are more operator- independent27. Evaluation of cerebral venous circulation by means of ultrasound has advantages in correlation with other methods; it is a reproducible, real- time method that provides information on vessel wall morphology and function, as well as on flow (a) characteristics and velocities.

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Fig. 7. Differences in the internal jugular vein cross section area in supine (a) and sitting (b) position. (b)

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References 16. Bašić Kes V, Zavoreo I, Šerić V, Vargek Solt- er V, Cesarik M, Hajnšek S, Bošnjak Pašić M, 1. Cornenwett JL, Gloviczki P, Johnston KV, Gabelić T, Silvio B, Soldo Butković S, Lusić Kempczinski RF, Krupski WC, Freishlag JA, I, Dežmalj Grbelja L, Vladić A, Bielen I, et al. Venous disease: an overview. In: Rutherford RB, Antončić I, Demarin V. Recommendations for diag- editor. Rutherford vascular surgery. Philadelphia: WB Saun- nosis and management of multiple sclerosis. Acta Clin Croat ders Co., 2000:1907-19. 2012;51(1):117-35. 2. Koeppen BM, Stanton BA. Overview of circulation. 17. Bašić Kes V, Cesarik M, Ćorić L, Zavoreo I, In: Berne RM, Levy MN, editors. Physiology, 6th edn. Rotim K, Beroš V, Pažanin L, Drnasin S, De- Philadelphia: Mosby Elsevier, 2009:289-291. marin V. Tumor-like multiple sclerosis. Acta Clin Croat 3. Sutton D, Stevens J. Vascular imaging in neuroradiol- 2012;51(1):113-6 ogy. In: SUTTON D, editor. Textbook of radiology and imag- 18. Singh AV, Zamboni P. Anomalous venous blood flow ing, Vol. 2. New York: Churchill Livingstone, 2003:1682-7. and iron deposition in multiple sclerosis. J Cereb Blood Flow 4. Ryan SP, Mc Nicholas MMJ. Central nervous system Metab 2009;29(12):1867-78. in anatomy for diagnostic imaging. London: WB Saunders 19. Zamboni P. The big idea: iron-dependent inflammation in Company Ltd., 1998:77-80. venous disease and proposed parallels in multiple sclerosis. J 5. Kido DK, Baker RA, Rumbaugh Calvin L. R Soc Med 2006;99(11):589-93. Normal cerebral vascular anatomy. In: Abrams HL, edi- 20. Levenson CW, Tassabehji NM. Iron and ageing; an tor. Abrams angiography, vascular and interventional radi- introduction to iron regulatory mechanisms. Ageing Res Rev ology, 3rd edn. Boston, USA: Little, Brown and Company, 2004;3(3):251-63. 1983:257-68. 21. žIVADINOV R, MARR K, CUTTER G, et al. Prevalence, 6. Einhaupl KM, Masuhr F. Cerebral venous and sinus sensitivity, and specificity of chronic cerebrospinal venous in- thrombosis – an update. Eur J Neurol 1994;1:109-26. sufficiency in MS. Neurology 2011;77(2):138-44. 7. Wolf BS, Huang YP, Newman CM. The superficial 22. Ghezzi A, Comi G, Federico A. Chronic cerebro- sylvian venous drainage system. Am J Radiol 1963;89:398. spinal venous insufficiency (CCSVI) and multiple sclerosis. 8. Parkash C, Bansal BC. Cerebral venous thrombosis. J Neurol Sci 2010;32(1):17-21. Indian Acad Clin Med 2000;5:55-61. 23. Ozsvath RR, CASEY SO, LUSTRIN ES, et al. Cerebral 9. Wasay M, Azeemuddin M. Neuroimaging of cerebral venography: comparison of CT and MR projection venogra- venous thrombosis. J Neuroimaging 2005;15:118-28. phy. AJR Am J Roentgenol 1997;169:1699-707. 10. Koeppen BM, Stanton BA. Properties of the vascula- 24. Bastianello S, ROMANI A, VISELNER G, et al. ture. In: Berne RM, Levy MN, editors. Physiology, 6th Chronic cerebrospinal venous insufficiency in multiple scle- edn. Philadelphia: Mosby Elsevier, 2009:330-69. rosis: clinical correlates from a multicentre study. BMC Neu- rology 2011;11:132. 11. Zamboni P, Galeotti R, Menegatti E, et al. Chronic cerebrospinal venous insufficiency in patients 25. Simka M, Kostecki J, Zaniewski M, Majewski with multiple sclerosis. J Neurol Neurosurg Psychiatry E, Hartel M. Extracranial Doppler sonographic criteria 2009;80(4):392-9. of chronic cerebrospinal venous insufficiency in the patients 12. BARTOLOMEI I, SALVI F, GALEOTTI R, et al. Haemody- with multiple sclerosis. Int Angiol 2010;29(2):109-14. namic patterns in chronic cerebrospinal venous insufficiency 26. Hojnacki D, Zamboni P, Lopez-Soriano A, in multiple sclerosis. Correlation of symptoms at onset and et al. Use of neck magnetic resonance venography, Dop- clinical course. Int Angiol 2010;29(2):183-8. pler sonography and selective venography for diagnosis of chronic cerebrospinal venous insufficiency: a pilot study in 13. Khan O, Filippi M, Freedman MS, et al. Chronic multiple sclerosis patients and healthy controls. Int Angiol cerebrospinal venous insufficiency and multiple sclerosis. Ann 2010;29(2):127-39. Neurol 2010;67(3):286-90. 27. Wattjes MP, van Oosten BW, de Graaf WL, et 14. Lee AB, Laredo J, Neville R. Embryological back- al. No association of abnormal cranial venous drainage with ground of truncular venous malformation in the extracranial multiple sclerosis: a magnetic resonance venography and venous pathways as the cause of chronic cerebrospinal venous flow-quantification study. J Neurol Neurosurg Psychiatry insufficiency. Int Angiol 2010;29(2):95-108. 2010;82(4):429-35. 15. Franceschi C. The unsolved puzzle of multiple sclerosis and venous function. J Neurol Neurosurg Psychiatry 2009;80(4):358.

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Sažetak

PROCJENA MOŽDANE VENSKE CIRKULACIJE ULTRAZVUKOM

I. Zavoreo, V. Bašić-Kes, L. Zadro-Matovina, M. Lisak, L. Ćorić, T. Cvjetičanin, D. Ciliga i T. Trošt Bobić

Venska cirkulacija obuhvaća plućne vene, sistemske vene i venske sinuse prisutne isključivo u lubanji. Cerebralni venski sustav dijeli se u dva glavna dijela, površinski i dubinski cerebralni venski sustav. Glavna zadaća venske cirkulacije je uklanjanje deoksigenirane krvi i štetnih tvari iz tkiva te njihovo odvođenje prema srcu. Vene u usporedbi s arterijama imaju tanju stijenku i veći lumen. U svakom trenu oko 60%-70% ukupnog krvnog volumena u tijelu nalazi se u venama. Glavni čimbenici koji utječu na funkciju venskog sustava su respiracijski ciklus, tonus vena, funkcija desne strane srca, gravitacija te funkcija mišićne pumpe. Venska cirkulacija se, općenito, može prikazati invazivnom metodom selektivne venografije i neinvazivnim metodama dopler sonografije, CT venografijom i MR venografijom. Cerebralni venski sustav prikazuje se selektivnom venografijom, moždanom CT venografijom, moždanom MR venografijom i specijaliziranom intrakranij- skom i ekstrakranijskom dopler sonografijom. Cilj ovoga rada je opisati mogućnosti prikazivanja venske cirkulacije glave i vrata pomoću metoda ultrazvučnog prikaza, naročito kronične venske insuficijencije kao jednog od najčešćih patofiziološ- kih entiteta koji se povezuju s nastankom neurodegenerativnih bolesti. Ključne riječi: Vene – radiografija; Vene – ultrazvuk; Moždane vene – ultrazvuk; Cerebrovaskularni poremećaji; Kronična cerebrospinalna venska insuficijencija; Transkranijska dopler sonografija; Zambonijev protokol

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