Contrast-enhanced MR angiography is not more accurate than unenhanced 2D time-of-flight MR angiography for determining > or = 70% internal carotid artery stenosis

Abstract

Background and purpose: Internal carotid artery (ICA) atheromatous disease is an important cause of ischemic stroke, and endarterectomy or stent placement is typically indicated for symptomatic patients with > or = 70% stenosis. Our purpose was to compare contrast-enhanced MR angiography (CE-MRA) with unenhanced 2D time-of-flight MR angiography (2D TOF MRA) in detecting hemodynamically significant ICA stenosis, by using CT angiography (CTA) as the reference standard.

Materials and methods: This was an institutional review board-approved retrospective study. We identified 177 consecutive patients (354 ICAs) who received correlative CE-MRA, 2D TOF MRA, and CTA. Two neuroradiologists blinded to the CTA data graded the degree of ICA stenosis according to a 5-point scale. Additionally, luminal signal-intensity characteristics including 1) signal intensity drop-out, 2) distal-vessel narrowing, and 3) distal-vessel signal-intensity reduction were recorded. MRA results were correlated with those of CTA, and receiver-operating-characteristic (ROC) curves were constructed.

Results: On CTA, there were 55 ICAs with and 299 without > or = 70% stenosis. CE-MRA was 84% sensitive and 96% specific for detecting > or = 70% stenosis; 2D TOF MRA was 80% sensitive and 95% specific. The area under the ROC curve was 0.97 for CE-MRA and 0.95 for 2D TOF MRA (P = .51, not significant). For both MRA studies, each of the luminal signal-intensity characteristics had high specificity (> 98%) but poor-to-mild sensitivity (35%-66%) in detecting > or = 70% stenosis.

Conclusions: Although it is established that CE-MRA more accurately delineates neurovascular anatomy than does unenhanced 2D TOF MRA, the administration of gadolinium did not offer a significant advantage in distinguishing surgically treatable ICA stenosis. This conclusion may be important in patients with contraindications to gadolinium.

Fig 1.

This ICA origin was rated by the observers to have severe (70%–95%) stenosis when imaged by all 3 techniques: 2D TOF MRA (A), CEMRA (B), and CTA (C–E). A and B, Signal-intensity drop-out is noted (arrow), but no distal narrowing or distal signal-intensity reduction is observed on MRA images. C, Curved reformatted CTA view of the left ICA demonstrating a severe stenosis (arrow). D, An axial image at the level of greatest narrowing (arrow). E, At the level of the NASCET reference diameter (arrow).

Fig 2.

A scatterplot of stenosis scores on CE-MRA and 2D TOF MRA (A) and ROC curves for CE-MRA versus 2D TOF MRA (B). The size of the marker on the scatterplot represents the relative frequency of stenosis scores.

Fig 3.

A, MRA of the neck with gadolinium demonstrating signal-intensity drop-out in the proximal left ICA (solid arrow), with decreased signal intensity and vessel narrowing (slim sign) in the distal ICA (dashed arrows), which is significantly smaller compared with the ipsilateral vertebral artery (double-tailed arrow). B, 2D TOF MRA image of the neck vasculature exemplifies distal-vessel narrowing/irregularity and distal-vessel signal-intensity reduction (white arrows).