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EDITORIAL Table of Contents   
Year : 2003  |  Volume : 13  |  Issue : 2  |  Page : 137-138
The carotid confusion


Editor-in-chief, The Indian Journal of Radiology and Imaging, India

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How to cite this article:
Desai SB. The carotid confusion. Indian J Radiol Imaging 2003;13:137-8

How to cite this URL:
Desai SB. The carotid confusion. Indian J Radiol Imaging [serial online] 2003 [cited 2019 Nov 18];13:137-8. Available from: http://www.ijri.org/text.asp?2003/13/2/137/28645
The carotid and vertebrobasilar circulation can be studied by colour Doppler ultrasound (CDUS), CT angiography (CTA), MR angiography (MRA) and catheter angiography. All these modalities have their advantages and disadvantages. The evaluation of the carotid and vertebrobasilar tree has been plagued by a plethora of studies culminating in a lot of confusion that I call the "CAROTID CONFUSION". Every now and then, we encounter a case where we, as one medical team, have faltered and we begin to question our decisions regarding the imaging modality, our confidence level in making the diagnosis and our decisions on patient management. I am so often asked about how I decide which patient should undergo a catheter angiography and which a time-of-flight MRA (TOF MRA) that I decided to address the issue in this editorial.

The current management of atherosclerotic disease of the carotids is based on the NASCET trial which divides the stenosis into four grades, mild (0-29%), moderate (30-69%), severe (70-99%), and occlusion (100%). Symptomatic stenosis of the internal carotid artery 70-99 % correlates with high risk of cerebrovascular accident and benefits with carotid endarterectomy. It is necessary to make the difference between total occlusion and extremely narrowed lumen as the second group may benefit with stent placement or carotid endarterectomy. In about 10% of patients referred with carotid occlusion diagnosed on CDUS and unenhanced MRA, patent vessels above very high-grade stenosis was found on CTA and Revascularisation with endarterectomy could be performed. In the preoperative evaluation of endarterectomy candidates, disease requiring surgery (severe stenosis) must be differentiated from disease that does not require surgery (normal, mild, moderate stenosis and occlusion).

A lot of studies have been performed comparing the sensitivity, specificity, and accuracy of CDUS, CTA, MRA and catheter angiography. In a study by Bruno et al 44 carotid arteries in 22 patients were evaluated by CTA, CE-MRA and catheter angiography. They found that severe internal carotid artery stenosis was detected with a sensitivity and specificity of 100% each with CTA and 93% and 100% respectively with CE-MRA. Luminal surface irregularities were most frequently seen at CT angiography. CT angiography and enhanced MR angiography detected more ulceration than catheter angiography [1]. Nederkoorn et al studied 350 symptomatic patients with duplex ultrasound, MRA and catheter angiography. Catheter angiography being the standard, they found that duplex ultrasound had a sensitivity and specificity of 87.5% and 75.7% respectively and MRA 92.2% and 75.5% respectively for detecting severe (70-99%) stenosis [2]. Lubezky et al found that CTA has a significantly higher positive predictive value (95%) than duplex ultrasound (77%)for diagnosing occlusion[3]. Lev et al found that CTA can distinguish total ICA occlusion from residual hairline lumen with high degree of accuracy[4]. New and Roubin compared the results of CDUS and catheter angiography in 225 patients referred for carotid intervention[5]. They found that mild lesions were diagnosed by ultrasound with a sensitivity of 54%, specificity of 89%, and a positive predictive value of 89% compared with angiography. However for severe lesions ultrasound had a sensitivity of 93%, a specificity of 67%, and a positive predictive value of 45%. They concluded that using ultrasound as the sole diagnostic test to determine the severity of a carotid stenosis may result in a high number of inappropriate operations and a large proportion of patients who may not be offered treatment due to false negative diagnoses.

These four imaging modalities can be broadly classified into two groups; volume dependent imaging in which the vessel is filled with contrast material like CTA, contrast enhanced MRA (CE-MRA) and catheter angiography and flow / velocity dependent imaging that includes CDUS and TOF MRA. CDUS is a good screening tool as it is cost-effective, freely available and has high accuracy in defining the normal and mild stenosis group who would need no aggressive treatment. However it is highly operator dependent. The flow / velocity dependent imaging modalities i.e. CDUS and unenhanced MRA are not accurate in defining the extremely narrowed lumen group separate from total occlusion. It is here that volume dependent imagings like CTA, CE-MRA and catheter angiography have an advantage. CTA has the additional advantage of being fast and detecting plaque morphology better than the other modalities. From analysis of a large number of comparative studies, it appears that as we stand today in 2003 in the era of multislice CT, CTA has a higher accuracy in grading internal carotid artery stenosis and occlusion, convincingly showing the distal flow in apparent totally occluded vessel, diagnosing tandem lesions and studying intracranial circulation in the shortest time and is sometimes even better than gold standard catheter angiography[6].

 
   References Top

1.Randoux B, Marro B. Koskas F et al Carotid artery stenosis: prospective comparison of CT, three-dimensional gadolinium enhanced MR and conventional angiography. Radiology 2001;220:179-185  Back to cited text no. 1    
2.Nederkoorn PJ, Mali WP. Preoperative diagnosis of carotid artery stenosis: accuracy of noninvasive imaging. Stroke Aug 2002;33(8):2003-2008   Back to cited text no. 2    
3.Lubezky N, Fajer S, Barmer E, Karmeli R. Duplex scanning and CT angiography in the diagnosis of carotid artery occlusion: a prospective study. Eur J Endovasc Surg Aug 1998; 16(2):133-6.  Back to cited text no. 3    
4.Lev MH, Romero JM, Goodman DNF et al. Total occlusion versus hairline residual lumen of the internal carotid arteries: accuracy of single section helical CT angiography. AJNR Am J Neuroradiol June/July 2003;24:1123-1129.  Back to cited text no. 4    
5.New G, Roubin GS. Validity of duplex ultrasound as a diagnostic modality for internal carotid artery disease. Cather Cardiovasc Interv. Jan 2001;52(1):9-15  Back to cited text no. 5    
6.2003 Department of Neurosurgery, University of Pittsburgh, Occlusive Vascular Disorders  Back to cited text no. 6    

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Correspondence Address:
Shrinivas B Desai
Editor-in-chief, The Indian Journal of Radiology and Imaging
India
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