Journal of Non Invasive Vascular Investigation Category: Clinical Type: Review Article
Spontaneous Cervical Arterial Dissection: Several Aspects of Magnetic Resonance Imaging
- Dreval\' Marina Vladimirovna1*, Kalashnikova Lyudmila Andreevna2, Dobrynina Larisa Anatol\'evna2, Sergeeva Anastasiya Nikolaevna2, Doronina Elena Viktorovna2, Krotenkova Marina Viktorovna2, Michael Piradov2
- 1 Department Of Radiology, Research Center Of Neurology, Junior Researcher, Moscow, Russian Federation
- 2 Department Of Radiology, Research Center Of Neurology, Moscow, Russian Federation
*Corresponding Author:Dreval\' Marina Vladimirovna
Department Of Radiology, Research Center Of Neurology, Junior Researcher, Moscow, Russian Federation
Tel:(+7) 495 490 2205,
Received Date: Oct 11, 2016 Accepted Date: Feb 28, 2019 Published Date: Mar 14, 2019
Definition, epidemiology and pathogenesis
SAD incidence is approximately 5 cases per 100,000/year . These numbers are probably undersized since dissection as the cause of ischemic stroke often remains undetected, or it may be associated with subtle clinical symptoms or even no symptoms at all, and may become evident only on neuroimaging study, angiography or ultrasound imaging. SAD rates are similar in men and women, and in vast majority of cases (90%) it affects young people .
According to pathological studies, the cause of SAD may be dysplastic changes of artery wall, and, substantially less often, undifferentiated connective tissue disorders, arteritis, Ehlers-Danlos vascular syndrome, Marfan syndrome, cystic medial necrosis [7,8]. Some authors suggest that arteriopathy underlying SAD may be temporary [3,9]. The provoking factors can be minor injury of head or neck, physical strain, manipulations with neck, long-lasting uncomfortable position of head, preceding infection .
Dissection more often develops in the extra-cranial parts of the vessels, namely in the cervical part of Internal Carotid Artery (ICA) and in V2 and V3 segments of Vertebral Artery (VA). This may be explained by greater mobility of the arteries on these levels and their anatomic proximity to osseous structures (e.g., cervical vertebrae, styloid process) .
MRA includes Time of Flight (TOF), Phase Contrast (PC) and Contrast Enhanced (CE) techniques. Like digital subtraction angiography, all MRA methods allow revealing of typical signs of abnormal changes of artery lumen due to dissection. They include extended regular (“string sign”; Figure 1) or irregular stenosis (“wavy ribbon sign”; Figures 2, ? and b). Narrowing of internal carotid artery usually occurs in its cervical part (on the level of C1 and C2 cervical vertebrae), starts for 2-3 cm more distally than the bulb and ends before the entrance to petrous part of temporal bone. Stenosis of vertebral artery is usually localized in the V2 segment on the level of C3, C4 and C5 cervical vertebrae . More than in 20% cases the VA dissection includes intracranial expansion of the lesion .
In the occlusion of ICA due to the dissection, angiographic signs are less specific; as the similar angiographic presentation is observed in occlusion resulted from atherothrombosis. The typical sign of ICA occlusion due to the dissection that may be seen in some patients is the pre-occlusive tapered stenosis, known as the “candle flame” or “rat tail” sign (Figure 3) .
Other pathognomonic angiographic signs of dissection are formation of dissecting aneurysm (Figures 4, ? and b) and double artery lumen (true and false; Figures 5, ? and b).
Dissecting aneurysm is the local broadening of artery lumen and is often located precranialy in cervical part of ICA or in V2 segment of VA [12; 3]. In our recent study we demonstrated that the most often angiographic signs of dissection of VA and ICA is the irregular prolonged stenosis, while other typical signs are seen significantly less often; e.g., tapered pre-occlusive narrowing of artery was seen only in ICA (28%), and in VA this sign was not detected. Formation of double lumen is characteristic only for VA and it was observed only in 8% of cases .
The advantage of MRA compared to DSA is the opportunity to visualize the arterial wall and to reveal the signs of IMH. For this purpose ?1 fat suppression (f/s) weighted image (WI) and ?2 f/s WI in parallel (coronary) and perpendicular (axial) planes relatively to the path of main arteries of neck are used. Dissection is associated with the increase of outer diameter of artery, decrease of diameter and eccentric positioning of artery lumen. IMH in the axial plane is seen as an area of semi lunar form with sharp contours that surrounds the arterial lumen like a cuff. Intensity of MR-signal from IMH is determined by paramagnetic properties of products of haemoglobin decay, and its changes over time have some common features with the decay of intracerebral haematoma (Figure 6) .
In the acute stage of the dissection (on days from 1 to 3) IMH has is intensive signal on?1WI (Figure 7, ?) and hypo-intensive signal on ?2WI (Figure8, ?), that makes it difficult to distinguish it from surrounding tissues. Then MR-signal from IMH becomes slightly hyper intensive on ?1WI (Figure 7, b) and high intensive on ?2 (Figure 8, b). By the end of the first week signal from IMH becomes hyper intensive on ?2WI as well as on ?1WI sequences (Figure 7, c).
Gradual further decrease of signal intensity in IMH leads to inability to visualize it in 2-3 months after hematoma formation . The issue of differentiating diagnosis of intra-arterial thrombosis and dissection that caused occlusion of artery lumen often arise . Usually intra-arterial thrombosis is caused by white thrombus. To our data, it produces less intensive signal on?1WI (Figure 9, b) compared to IMH (Figure 9, ?), since it contains less haemoglobin and products of haemoglobin decay than IMH . Another distinguishing feature of IMH vs. intra-arterial thrombosis is increase of outer arterial diameter in case of dissection.
Hyper-intensive signal from fat tissue surrounding artery can be falsely identified as IMH. Therefore, imaging sequences with fat suppression are of high importance . Hyper-intensive MR-signal in vertebral venous plexus in transverse openings of cervical vertebrae due to slow blood flow may mimic sub acute IMH in the vertebral artery thus producing false-positive result. One should carefully assess the arterial lumen (it is normal if hyper-intensive signal comes from the venous plexus) and to check if there is a linear area of decreased MR signal intensity between the lumen of artery and IMH corresponding to intima on TOF MRA . Atheromatous plaque may imitate local dissection of artery appearing as hyper-intensive rim on ?2WI. However, this rim usually produces isointensive MR signal on ?1WI by contrast with hyper-intensive sub acute IMH . False-negative results are often in first days after the lesion, when IMH does not produce hyper-intensive signal and blends into surrounding tissues (Figure 7, ?).Therefore, in hyper acute stage of suspected dissection careful estimation of MRA data for the signs of abnormality within arterial lumen is essential .
In addition to aforementioned ?1WI and ?2WI, TOF MRA may be also used for IMH imaging. This MRA technique provides an opportunity to visualize IMH due to lack of signal suppression in surrounding tissues with short T1 time (e.g., methaemoglobin within IMH) (Figure 10) .
Besides assessment of raw TOFMRA data, reconstructed Maximum Intensity Projection (MIP) image analysis is also extremely important. Usually MR signal from blood flow has higher intensity than signal from IMH. Source (raw) data allows visualization of the whole circle (diameter) of artery, and MIP reconstruction allows visualization of length and precise localization of dissection . There are several most common mistakes of TOF MRA image interpretation in suspected dissection. In some cases IMH is not revealed, as hyper-intensive signal from products of haemoglobin decay (methaemoglobin) mimics blood flow on MIP images (Figures 11, ? and b). Moreover, artefact of sensitivity from skull base bones on MIP images sometimes appears as irregularnarrowing of proximal part of petrous segment of internal carotid artery and by mistake, it may be considered as dissection, especially if this narrowing is asymmetrical .
It should be mentioned that another technique of non-contrast MRA, Phase Contrast (PC) ?R?, as well as Contrast-Enhanced (??) MRA depicts only lumen of the artery and does not allow direct IMH detection. PC MRA is used in diagnosis of dissection more rarely than TOFMRA or CE MRA. The drawback of ?? MRA in comparison with DSA is lower spatial and temporal resolution; however, minimal invasiveness, absence of ionizing radiation, availability of the technique in outpatient setting are amongits undeniable advantages. The disadvantage of TOFMRA is low sensitivity to slow blood flow and poor ability to visualize curved portions of blood vessels due to lack of laminar circulation of blood and formation of turbulence. The advantage of ?? MRA and TOFMRA in comparison to DSA is readily available extension of the study with ?2 f/s and ?1 f/s WIs with focus on stenotic portion of the artery to prove or to exclude dissection. Combination of MRI and MRA provides not only effective diagnostics of dissection, but it also can be used as non-invasive approach to monitor IMH regress over time or development of complications .
As the development of dissection is dynamic process, changes of IMH are associated with changing of angiographic picture. Thus, stenosis of internal carotid artery and vertebral artery resolve completely or partially in 2-3 months that is the important sign of dissection (Figures 12, ? and d).
By contrast, occlusions due to dissection resolve only in half of cases , and the level of residual stenos is in all cases is usually does not exceed 20% (Figures 13, ? and d) .
In 1/3 of cases dissecting aneurysms regress completely, about 40% decrease in size. However, the double lumen of artery that developed in the acute period of dissection remains unchanged .
In the Research Center of Neurology we use the following protocol for patients with suspected cerebral artery dissection:
- MRI of brain tissue(?2, ?1, ?2 FLAIR, SWI, DWI with ADC mapping);
- 3D TOFMRA of extra and intracranial arteries;
- ?1 f/s and ?2 f/s WIs of major arteries of head and neck in coronary and axial planes.
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Citation:Vladimirovna DM, Andreevna KL, Anatol'evna DL, Nikolaevna SA, Viktorovna DE, et al. (2019) Spontaneous Cervical Arterial Dissection: Several Aspects of Magnetic Resonance Imaging. J Non Invasive Vasc Invest 4: 014.
Copyright: © 2019 Dreval\' Marina Vladimirovna, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.