Scholarly article on topic 'Magnetic resonance angiography in evaluation of acute intracranial steno-occlusive arterial disease'

Magnetic resonance angiography in evaluation of acute intracranial steno-occlusive arterial disease Academic research paper on "Clinical medicine"

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{"Intracranial MRA" / "Steno-occlusive arterial diseases" / Stroke}

Abstract of research paper on Clinical medicine, author of scientific article — Moustafa E.M. Radwan, Khaled O. Aboshaera

Abstract Objectives Assessment of the diagnostic usefulness of MRA in evaluation of patients with acute intra cranial steno-occlusive arterial disease. Patients and methods 84 patients with acute intracranial steno-occlusive arterial disease were subjected to the following brain MRI protocol: Axials DWI, T1WI, T2WI, FLAIR, T2∗ Gradient Echo Imaging and 3D TOF MRA. Results Eighty four patients (M/F=49/35) aged between 28 and 86years. MRA findings of arterial segments correlated with location of the ischemic lesions described by different MRI sequences including the DWI in all cases (100%). MRA of the intracranial vessels revealed 60 arterial segments with occlusions/absent flow. Occlusions were most common in MCAs (n =45) followed by PCAs (n =9). 31 arterial segments with stenosis were seen, and they were mainly affecting arterial territories of PCAs (n =16). Atheromatous plaques were identified at the Lt. ICA in 3 cases and in Rt. ICA in 2 cases, absent A1 segment of Rt. ACA (n =12), absent A1 segment of Lt. ACA (n =2), dominant Rt. VA (n =6), dominant Lt. VA (n =4) and Dolichoectasia of BA (n =4). Conclusions MRA provides early detailed diagnosis of occlusive intracranial arterial disease through detection of exact site of arterial affection.

Academic research paper on topic "Magnetic resonance angiography in evaluation of acute intracranial steno-occlusive arterial disease"

The Egyptian Journal of Radiology and Nuclear Medicine (2016) 47, 903-908

Egyptian Society of Radiology and Nuclear Medicine The Egyptian Journal of Radiology and Nuclear Medicine

www.elsevier.com/locate/ejrnm www.sciencedirect.com

ORIGINAL ARTICLE

Magnetic resonance angiography in evaluation of c^Ma* acute intracranial steno-occlusive arterial disease

Moustafa E.M. Radwana,c*, Khaled O. Aboshaerab

a Department of Radiodiagnosis, Assiut University, Egypt b Departments of Neurology and Psychiatry, Assiut University, Egypt

c Department of Radiodiagnosis, Taibah University, Al-Madinah Al Munwarah, Saudi Arabia

Received 29 April 2016; accepted 31 May 2016 Available online 24 June 2016

KEYWORDS

Intracranial MRA; Steno-occlusive arterial diseases; Stroke

Abstract Objectives: Assessment of the diagnostic usefulness of MRA in evaluation of patients with acute intra cranial steno-occlusive arterial disease.

Patients and methods: 84 patients with acute intracranial steno-occlusive arterial disease were subjected to the following brain MRI protocol: Axials DWI, T1WI, T2WI, FLAIR, T2* Gradient Echo Imaging and 3D TOF MRA.

Results: Eighty fourpatients (M/F = 49/35) aged between 28 and 86 years. MRA findings of arterial segments correlated with location of the ischemic lesions described by different MRI sequences including the DWI in all cases (100%). MRA of the intracranial vessels revealed 60 arterial segments with occlusions/absent flow. Occlusions were most common in MCAs (n = 45) followed by PCAs (n = 9). 31 arterial segments with stenosis were seen, and they were mainly affecting arterial territories of PCAs (n = 16). Atheromatous plaques were identified at the Lt. ICA in 3 cases and in Rt. ICA in 2 cases, absent A1 segment of Rt. ACA (n = 12), absent A1 segment of Lt. ACA (n = 2), dominant Rt. VA (n = 6), dominant Lt. VA (n = 4) and Dolichoectasia of BA (n = 4).

Conclusions: MRA provides early detailed diagnosis of occlusive intracranial arterial disease through detection of exact site of arterial affection.

© 2016 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-

nd/4.0/).

1. Introduction

Steno-occlusive arterial disease is the commonest cause of ischemic stroke all over the world where the thromboembolic

* Corresponding author at: Department of Radiodiagnosis, Faculty of

Medicine, Assiut University, Assiut, Egypt.

E-mail address: ezeldienmos@yahoo.com (M.E.M. Radwan).

Peer review under responsibility of The Egyptian Society of Radiology

and Nuclear Medicine.

causes account for about 85% of stroke cases (1). A high incidence of the disease was reported in African and Asian populations (2,3). Proper and accurate assessment of arterial diseases that underlie development of stroke is essential in patient management and follow-up (4).

Previously, assessment of atherosclerotic disease within intracranial vessels was not well-appreciated clinically. This might be due to the inability to visualize intracranial vessels non invasively or due to the greater emphasis on the more easily imaged carotid arteries (5). It was reported that intracranial

http://dx.doi.org/10.1016/j.ejrnm.2016.05.023

0378-603X © 2016 The Egyptian Society of Radiology and Nuclear Medicine. Production and hosting by Elsevier. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

vessel diseases may precede extracranial atherosclerosis. This sequence was suggested after noticing that substantial carotid stenosis is absent in a group of patients with intracranial atherosclerosis, while nearly all those with extracranial stenosis also had concomitant intracranial stenosis. Examining extracranial arteries without assessment of intracranial arteries will diagnose the arterial atherosclerosis in its advanced stages, while examining the intra cranial arteries will diagnose the disease in its early stages enabling the clinicians to intervene earlier (6,7).

The protocols of MR imaging in stroke patients are not standard across institutions (8). Adding magnetic resonance angiography (MRA) to the imaging protocol improves both diagnosis and clinical management (9,10). The sequence, however is not routinely done in stroke imaging in all centers. MRA can track the changes in the vessel lumen with time (11). Imaging of the vessels can reliably answer questions about the mechanism of the stroke, whether it is thrombotic, embolic or homodynamic. It also assesses the risk of future events by identifying whether there is occlusive arterial disease, localizing the exact site of occlusion and by determining the pathology underlying the stroke such as atherosclerosis or dissection (12). MRA can also identify other vascular lesions such as malformation, aneurysms and arterial compression (9).

Time of flight (TOF) MRA technique gives the managing physician an idea of the overall cerebral vascular channel morphology and thus has an important prognostic and prophylactic value in the patient's management (13). Moreover, MRA has a potentially important role in appropriate patient selection for intra-arterial fibrinolysis, in patient's follow-up and monitoring of therapeutic efficacy (8,14). A normal or near-normal MRA of the intra cranial arteries can effectively exclude the possibility of a high-grade arterial stenosis (15,16).

The aim of the current study was to assess the diagnostic usefulness of MRA in evaluation of patients with intra cranial steno-occlusive disease.

2. Patients and methods

2.1. Patients

Overall 112 patients with symptoms indicative of acute ischemic cerebrovascular insult were originally enrolled into this study; Inclusion Criteria were patients who were imaged with MRI and MRA within 2 days of symptom onset. Exclusion criteria were patients who did not have MRA in their MRI protocol of examination (n = 22) and patients with a non-diagnostic MRA due to major artifacts (n = 6). Image and data analyses were done for 84 patients who fulfilled the criteria of acute intracranial steno-occlusive arterial disease. This prospective study was conducted in the University Hospital between March 2012 and September 2015 after approval of institutional board of ethics and obtaining informed consent.

2.2. Methods of examinations

All patients were subjected to the following:

(1) Full history taking and clinical examination: History was taken from the patients or informant. Neurological clinical examination was conducted to define the cerebral artery territory affected.

(2) Radiological and Imaging Investigations: Brain MRI was acquired within 2 days of onset, using 1.5-Tesla Philips Superconducting Magnet System (Gyroscan ACS-NT) power track 6000 at Assiut University Hospital according to the following protocol: Axials: Diffusion Weighted Imaging (DWI), T1 Weighted Imaging (T1WI), T2 Weighted Imaging (T2WI), Fluid Attenuated Inversion Recovery technique (FLAIR), T2* Gradient Echo Imaging and Three dimensional time of flight intra cranial MRA (3D TOF MRA).

2.2.1. Axial intracranial (3D TOF MRA)

Intra cranial MRA was performed for the vertebro-basilar system including the posterior cerebral arteries, the intracranial internal carotid system, including the middle cerebral and the anterior cerebral arteries, at level of circle of Willis, with settings of TR35, TE 7.2, Flip angle 20°, images interpolated to 1.5-mm slice thickness, matrix 200 x 512, field of view 20, scan time 6.18 min and superior saturation band. MRA images were processed with a maximum intensity projection 3 dimensional time-of-flight technique. Review of the source images with the post processing images (maximum intensity projection, MIP) was done to overcome any overestimation of the degree of stenosis or any possible artifacts from MIP images.

2.2.2. Image analysis

Assessment was done for the intracranial vessels: middle cerebral arteries (MCAs), anterior cerebral arteries (ACAs), intracranial internal carotid arteries (ICAs), posterior cerebral arteries (PCAs), vertebral arteries (VAs), and the basilar artery (BA). MRA findings which signify affection of intra cranial arteries were recorded as stenosis (segmental flow gap or lumi-nal stenosis >50%), occlusion (non-visualized vessel segment with absent distal flow), atherosclerotic changes of the vessels and presence of plaques.

MRA findings were recorded and correlated with distribution of signal abnormalities seen in the MRI sequences. Arterial lesions corresponding to the location/territory of the recent infarcts on DWI were considered symptomatic.

2.3. Statistical methods

Descriptive statistical analysis was done with IBM SPSS Statistics software release 21, SPSS Inc., for windows (Microsoft). Data were collected, checked, coded and entered. Statistical methods included descriptive analysis such as mean ± standard deviation, number and percentage, frequencies, sensitivity and significant tests.

3. Results

Intracranial vessels of 84 patients with findings of acute intracranial steno-occlusive arterial disease were assessed using MRA. Forty-nine (58.3%) of patients were males and the remaining 35 (41.7%) were females, and their age ranged from 28 to 86 year with a mean age of 59.9 ± 9.7 year.

Sixty arterial segments with occlusions/absent flow within the arterial territories were detected. Occlusions were most common in Lt. MCA (n = 26); (absent flow at M1 segment (n = 11), M2 segment (n = 8) and M3 segment (n = 7), Rt.

Table 1 MRA findings in each of the examined arterial segments.

Rt. side Lt. side BA

Rt. ICA Rt. ACA Rt. MCA Rt. PCA Rt. VA Lt. ICA Lt. ACA Lt. MCA Lt. PCA Lt. VA

Occlusion (Absent Flow) 1 0 M1 13 5 0 1 3 M1 11 4 0 1

M2 4 M2 8

M3 2 M3 7

Stenotic Segment 0 1 0 6 1 0 1 M1 2 10 3 7

Mild atherosclerotic changes 47 38 51 54 46 51 47 48 53 46 47

Plaque 2 0 0 0 0 3 0 0 0 0 0

ICA indicate intracranial internal carotid artery; ACA, anterior cerebral artery; MCA, middle cerebral artery; M1, M2 and M3 = segments of MCA; PCA, posterior cerebral artery; BA, Basilar artery and VA, vertebral artery.

MCA (n = 19) (absent flow at M1 segment (n = 13), at M2 segment (n = 4) cases and at M3 segment (n = 2); Rt. PCA (n = 5), Lt. PCA (n = 4), Lt. ACA (n = 3), Rt. ICA, Lt. ICA and basilar artery in one case.

Thirty-one arterial segments with stenosis were seen. Steno-tic segment within the arterial territories was mainly seen in the Lt. PCA (n = 10), BA (n = 7), Rt. PCA (n = 6); Lt VA (n = 3); M1 segment of Lt. MCA (n = 2), Rt. ACA, Lt. ACA and Rt. VA in one case.

Mild atherosclerotic changes were detected in multiple arterial segments. Definite atheromatous plaques were detected at the left ICA in 3 cases and in Rt. ICA in 2 cases (Table 1).

Hypertension and Diabetes Mellitus are the common risk factors implicated in most atherosclerotic disease processes. In the studied patients, hypertension was present in 44% (n = 37 patients); 30 out of those 37 hypertensive patients had atherosclerotic changes in their intra cranial arteries. Diabetes Mellitus was present in 14.2% (n = 12 patients); 11 out of those 12 diabetic patients had atherosclerotic changes in

Table 2 Distribution of single arterial segments affection in the examined cases.

Arterial territory affected No. of patients

Right MCA distribution 11

Left MCA distribution 16

Right PCA distribution 6

Left PCA distribution 5

Basilar artery distribution 5

their intra cranial arteries and those 11 patients were hypertensive and diabetic at the same time.

In this study, single arterial segment affection was seen in 46 patients mainly affecting the MCAs (n = 27); Lt. MCA (n =16) and Rt. MCA (n = 11), followed by PCAs (n = 11); Rt. PCA (n = 6) and Lt. PCA (n = 5) and BA (n = 5) (Table 2). Simultaneous multiple arterial territorial affection (affection of P2 arterial segments in the same patient) was seen in 38 patients.

MRA steno-occlusive findings of arterial segments correlated with the location of the ischemic lesions described by MRI sequences including the DWI in all cases (100%). The sites of infarction were cortical infarcts (n = 7) and territorial infarcts (n = 66). These locations of infarcts signify that the cause of the infarction is more likely to be due to cardioem-bolism or extra cranial carotid artery disease. While lacunar infarcts (n = 33) and border zone infarcts (MCA/PCA) (n = 6) signify that the cause of the lesions is most probably due to atherosclerotic changes of intra cranial vessels.

Different MRA variants were detected in our patients, absent A1 segment of Rt. ACA was detected in 12 patients, absent A1 segment of Lt. ACA was detected in 2 patients, dominant Rt. VA in 6 patients, and dominant Lt. VA in 4 patients. Dolichoectasia of basilar artery was defined in 4 patients. Examples of the MRA findings are seen in Figs. 1-3.

4. Discussion

The present study examined intracranial vasculature affection in patients presented with acute intracranial steno-occlusive arterial disease. The total number of arterial segments

Fig. 1 (a) DWI b1000 shows bright signal of acute infarction in the left basal ganglia. (b and c) 3D TOF MRA shows occlusion of Lt. MCA at the junction of M1 and M2 segments, associated Dolichoectasia of basilar artery.

Fig. 2 (a) DWI b1000 shows bright signal of acute infarction in the left middle cerebral peduncle, (b and c) 3D TOF MRA shows stenotic segment at the M1 segment of the left MCA, atherosclerotic changes of the posterior circulation with multiple stenotic segments detected at the basilar, posterior cerebral arteries more on the left PCA. NB: associated dominance of Rt. Vertebral artery.

affection with occlusion or with stenosis was mostly seen in MCAs followed by affection of arterial segments of PCAs. The least intra cranial arterial segments affection was seen in the ACAs. All affection of ACA was multiple simultaneous arterial territorial affection with no isolated ACA affection. These results go with the reported findings of studies by Anne et al. (17) and Moustafa et al. (18) where the majority of strokes was found to be due to affection of the MCA territory followed by the PCA territory. This is probably reflecting the relative distribution of total brain blood supply. The ACA usually possesses good collateral flow through its paired contralateral vessel, and thus isolated ACA infarcts are rare (17,18). In another study done by Kim et al. (19), MCA stenosis was found to be the most common type of atherosclerotic lesions in approximately one-third of stroke patients. Authors explained these results by that MCA is the largest and the most direct branch of the ICA and is therefore the most one subjected to embolism.

Multiple arterial territorial affection was seen in 45.2% and these findings correspond to the results of a study by Roh et al. (20) who suggested that the source of affection of the arterial territories may be proximal than the carotid arteries.

MRA findings of arterial segments that were seen in this study correlated with location of the ischemic lesions described by different MRI sequences including the DWI in all cases. These results match those reported by Moustafa et al. (18). These results also correspond to a similar study by Johnson et al. (21) who found the distribution of stenotic or occlusive vascular lesions correlated with the location of infarction in 56 of the 60 positive cases (93%).

Fourteen (16.6%) of the patients examined in this study showed absent A1 segment of ACAs; 12 showed absent A1 segment of the Rt. ACA and 2 showed absent A1 segment of the left ACA. It was reported that a normal variation of ACA anatomy does occur in 10% of individuals in the form of hypoplasia or aplasia of one of the A1 segments with supply to the ipsilateral A2 segment via the anterior communicating branch from the contralateral ACA (22). This variant increases the risk and extent of neural tissue ischemia in the frontal lobe region during intravascular procedures performed in the area of anterior communicating artery or during ischemic episodes (22). As the ACA usually possesses good collateral flow through its paired contralateral vessel, isolated ACA infarcts are rare (19).

In our patients, dominance of Rt. VA was seen in 19% of the patients while dominance of Lt.VA artery was seen in 4.7%. This corresponds to the findings of Akgun et al. (23)

where left VAs were dominant in 19.3% of the cases while right VAs were dominant in 3% of the cases. Unequal VA flow is an important hemodynamic contributor of development of peri-vertebrobasilar junctional infarcts (24).

Vertebrobasilar dolichoectasia (VBD) is a condition characterized by ectasia, elongation and tortuosity of the basilar artery. It may be presented clinically by compression of the

Fig. 3 (a) Diffusion b1000 and (b) T2WI showing large acute Rt. Parietal cortical and subcortical infarction bright in DWI and T2WI, extending from the Rt. Sylvian fissure to the right parieto-occipital region, old infarction (hypo intense in Diffusion b1000 with hyperintense signal in T2WI and encephalomalacia in the Rt). Parieto-occipital region, involving also the right forceps major bright in T2WI. (c) 3D TOF MRA revealed occlusion at the junction of M1 and M2 segments of Rt. MCA, petrous portion of Rt. ICA shows inhomogeneous flow suggesting Rt. ICA plaque. NB: associated finding is absent A1 segment of Rt. ACA (normal variant).

cranial nerves or ischemic symptoms. In the current study, VBD was seen in 4.7% and this corresponds to the study by Ubogu et al. (25) who detected VBD in 3.2% of cases.

Because patients with acute cerebral ischemia may be critically ill, and examination time should also be kept within reasonable limits. Therefore the initial imaging evaluation should be limited to the acquisition of truly useful information only, taking into account the available therapeutic options at a given place at any given time (10). In this current study adding 3D TOF MRA to the MRI imaging protocol added 6.18 more minutes to the 7 min protocol which is reasonable time compared to the benefits gained by adding it to the usual protocol especially in acute phase of stroke as MRA provides early positive diagnosis of occlusive intracranial arterial disease that has a potentially important role in appropriate patient selection for intra-arterial fibrinolysis, by providing a relatively easy, non-invasive, time-efficient and straightforward screening procedure for the determination of the site of intracranial occlusion at the same time as routine MRI evaluation of the brain is performed.

In the current study MRA was the only used imaging modality for studying intra cranial vasculature with no data from other imaging modalities to be compared with. According to information published in the literature in comparing MRA with the other imaging modalities in examination of intra cranial vasculature, the following can be concluded. CT angiography can readily define intra cranial vascular map in a few seconds. However the major disadvantages of this technique are requirement for ionizing radiation and iodinated contrast media that have potential nephrotoxic effects (8-10). On the other hand, 3D TOF MRA was performed without contrast medium and did not require ionizing radiation. In previous studies, TOF MR Angiography was reported to be more sensitive than CT angiography in demonstrating intrac-erebral arteries especially in equipment with high magnetic field (11). Some of the potential disadvantages of the MR angiography are relatively longer imaging time, susceptibility to motion artifacts, and the same contraindications for any MRI examination (23). Detection of vessel occlusion with Doppler sonography is time consuming, highly dependent on examiner experience, and may technically not be possible, whereas a short fast MR angiography sequence offers this information. MRA is not an operator dependent technique, unlike conventional angiography and Doppler sonography when used in assessment of cerebral arteries (10).

At present, in evaluation of a stroke patient, not only MRI but also all other imaging modalities cannot define in which patients vessel occlusion will persist and in which patient's vessel recanalization will occur. However MRI can provide very important information about who may profit from recanaliza-tion, in whom recanalization should be tried, and in which patients there is no tissue at risk or no ischemic disease at all but only an excessive risk of hemorrhage due to thrombolytic therapy (26).

5. Conclusions

MRA provides early detailed diagnosis of occlusive intracra-nial arterial disease and vascular lesions demonstrated on intracranial MRA show a high correlation with infarct distribution. MRA has the advantages of not being operator dependent, no radiation or contrast media hazards and provides

important information adjunctive to conventional MRI in appropriate patient selection for intra-arterial thrombolysis, by providing a relatively easy, non-invasive, time-efficient and straightforward screening procedure for the determination of the site of intracranial occlusion at the same time as routine MRI evaluation of the brain is performed.

Conflict of interest

Authors declare no conflict of interest.

Authors' contributions

MR: carried out the design of the study, the acquisition, analysis and interpretation of data, as well as drafting and revising of the manuscript.

KO: clinical assessment of patients, taking part in data interpretation and drafting manuscript.

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