Evaluation of carotid artery stenosis with magnetic resonance imaging: Comparison with conventional anjiyography and ultrasonography

Cerebrovascular accidents have been a major reason of mortality and morbidity for older patients. Atherosclerosis is a degenerative process leading to plaque formation on vascular walls. In this process lipid and cholesterol granules, necrotic cell collection or bleeding could be detected inside the plaque. Plaque can lead to emboli, thrombosis or stenosis that might cause stroke which is the third major reason of death in the world. The type of plaque rather than degree of stenosis, indicates the risk of embli. In our study we aimed to evaluate the structure of atherosclerotic plaque with MRI. MATERIALS AND METHODS In this study, we evaluated retrospectively procedures of 37 (29 male, 8 Female) patients applied to our clinic with cerebrovascular symptoms or early diagnosis of carotid artery stenosis between August 2011 and May 2013. The MRI of patients with symptoms or corresponding findings with plaques which led to 50 percent or more narrowing of the vascular lumen on ultrasound or Conventional angiography, evaluated retrospectively and compared to US and DSA findings. The plaque structure and stenosis rates detected on MRI and Ultrasound of patients that have underwent conventional carotid artery angiography procedure and found to be asymptomatic or symptomatic with %70 or more stenosis or symptomatic with %50-70 stenosis retrospectively evaluated and compared with each other. The images with high motion artifacts were not evaluated ,asymptomatic patients with %50-70 stenosis and or those who could not undergo DSA or MRI due to contrast agent allergy were kept out of study. RESULTS For data analysis we used SPSS (Statistical Package for Social Sciences) for Windows 15.0'' software. We studied 36 patients, 9 female (%25) and 27 male (%75) with age between 25 and 81 (mean 65.86±9.91). According to the Fischer-exact test there was no significant relation between plaque type, intra-plaque bleeding or fibrous cap rupture and accompanying hypertension, DM or smoking history. The association between stenosis rate detected with angiography and intra-plaque bleeding or fibrous cap rupture evaluated with Fischer-exact test. 19 patients with fibrous cap rupture and 17 of 20 patients with intra-plaque bleeding showed %70 or more stenosis. This association was statistically significant (p<0.05). But there was no significant association between plaque type detected in Ultrasound and stenosis ratio. 14 of plaques detected in stenotic area had Type 1 and 2 (group 1), 23 were type 3 (group2), 19 were type 4 (group 3) characteristics. On axial MRI images we detected cap irregularity related to fibrous cap rupture in 19 plaques (%42.2), signal alterations associated with intra-plaque bleeding in 20 plaques. 6 of fibrous cap rupture findings were seen in type 1 and 2 plaques (%21.1), 13 in type 3(%55). Cerebral hemispheres ipsilateral to plaques with intra-plaque bleeding and fibrous cap rupture, showed acute infarction findings in 7 patients, chronic infarction and acute lacunar infarction finding in 13 patients. In all axial MRI sequences, these calcifications were seen as linear hypo-intense spots. Fischer-exact test showed no association between amount of calcification and acute infarction (p>0.05). In all patients with MRI findings associated with encephalomalasic alterations that in diffusion MRI showed no alteraions related to acute infarction, we detected linear hypo-intense spots associated with preserved fibrous cap in different thicknesses and fatty rich necrotic core. There was a significant association between lipid core of Type 1 hypo-echogenic plaques and chronic ischemic alterations (p<0.05). Also according to the Fischer-exact test there was a significant association between intra-plaque bleeding or fibrous cap rupture and acute infarction (p<0.05). CONCLUSIONS New developments in treatment of carotid artery stenoses , have arisen the necessity for revision and improvement of diagnostic methods for more efficient usage. Due to low sensitivity of ultrasound in detection of intra-plaque bleeding and fibrous cap rupture, MRI has become prominent as a possible new modality for plaque classification.