[A critical appraisal of diagnostic imaging techniques in asymptomatic carotid stenosis]

Asymptomatic carotid artery plaques: use of magnetic resonance imaging to characterize vulnerable plaques in 6 cases

BACKGROUND

Echography is a convenient and noninvasive method of characterizing carotid artery plaques. However, recent reports suggest that multisequential MR imaging may yield better data regarding the instability of asymptomatic carotid artery plaques. Therefore, the goal of the present study was to show the useful information for asymptomatic carotid artery plaque.

METHODS

A total of 6 patients (5 men, 1 woman; age range, 62-76 years; mean age, 69.2 years) with carotid artery plaques, which were detected during medical check-up using carotid MR angiography and/or echography, underwent MR imaging. Two-dimensional TOF MR angiography, T1WI, and fat-suppressed, cardiac-gated, black-blood proton density image, and T2WI were obtained with a 1.5-T MR imager. All plaques underwent carotid endarterectomy and histological examination.

RESULTS

The MR imaging demonstrated high signals in at least one modality in 4 of 7 plaques. In the remaining 3 patients, MR imaging detected partial-high signals, which corresponded to histologically confirmed partial lipid core or hemorrhagic components in the fibrous tissues The TOF MR imaging showed 2 cases of thin fibrous caps, and MR imaging also showed a large mural thrombus in 1 patient.

CONCLUSIONS

Magnetic resonance imaging was useful in characterizing factors associated with plaque instability in patients with asymptomatic carotid artery plaques and may help guide therapeutic strategies for asymptomatic carotid artery plaques.

Gadolinium-Enhanced Versus Time-of-Flight Magnetic Resonance Angiography: What Is the Benefit of Contrast Enhancement in Evaluating Carotid Stenosis?

Accurate patient selection based on preoperative imaging is imperative to good risk reduction in patients undergoing carotid endarterectomy (CEA). The goal of this study was to assess the accuracy of gadolinium-enhanced magnetic resonance angiography (GE MRA) versus time-of-flight (TOF) MRA in the work-up of patients undergoing CEA. Patients undergoing CEA between 1999 and 2001 were identified from a prospectively maintained institutional database. GE or TOF MRA was obtained on extracranial carotid arteries (n = 319) in patients undergoing CEA. Stenosis on MRA images was graded as moderate (n = 76) or severe (n = 243) by an attending radiologist who was blind to duplex results. Duplex imaging was performed in an Intersocietal Commission for the Accreditation of Vascular Labs (ICAVL) accredited lab, and stenosis was stratified as moderate (50-79%, n = 76) or high (80-99%, n = 243) grade using University of Washington criteria. For each patient, the degree of stenosis as determined by MRA (GE versus TOF) was compared to percent stenosis on duplex. For moderate-grade lesions, GE MRA concurred with duplex in 11.1% (4/36), underestimated in 2.8% (1/36), and overestimated in 86.1% (31/36) of carotid arteries imaged. TOF MRA concurred with duplex in 35% (14/40), underestimated in 0% (0/40), and overestimated in 65% (26/40) of carotid arteries. High-grade lesions demonstrated improved concordance between MRA and duplex. For these lesions, GE MRA concurred with duplex in 95.6% (130/136) of carotid arteries imaged, never overestimated stenosis (0/136), and underestimated in 4.4% (6/136). TOF MRA concurred with duplex 96.3% (103/107), overestimated stenosis as an occlusion in 0.9% (1/107), and underestimated in 2.8% (3/107). In addition to neck visualization, the GE technique allowed simultaneous aortic arch imaging. This was accomplished in 79.1% (136/172) of all GE MRAs. Simultaneous aortic arch imaging was not technically feasible with TOF MRA. For moderate-grade lesions, both MR techniques are inaccurate predictors of degree of carotid stenosis and result in a significant overestimation of stenosis. Each technique demonstrates improved concordance with duplex ultrasound in the setting of severe carotid artery stenoses. The ability of GE MRA to simultaneously image the aortic arch and the neck may allow for detection of occult tandem lesions and other anatomic variations, which may be particularly important in preoperative planning for carotid artery stenting.