STENOSIS OF THE CAROTID BIFURCATION - SUBJECTIVE ASSESSMENT COMPARED WITH STRICT MEASUREMENT GUIDELINES

Preliminary results of the North American Symptomatic Carotid Endarter ectomy Trial (NASCET) have shown that endarterectomy is highly effecti ve in preventing stroke in patients with 70% to 99% stenosis of the ca rotid bifurcation. These results are based on specific linear measurem ent criteria comparing the residual diameter of the lumen with that of the normal carotid beyond the bulb. These criteria may differ from su bjective assessments of the severity of stenosis. Angiograms from 125 NASCET patients were analysed independently by three groups of reviewe rs. The first group consisted of three neuroradiologists, the second o f two neurologists and one neurosurgeon and the third of three radiolo gists with neuroradiologic experience. The degree of stenosis was esti mated, without measurement, as mild (1% to 29%), moderate (30% to 69%) or severe (70% to 99%), or the vessel was said to be occluded. These assessments were compared with the degree of stenosis as determined by the NASCET neuroradiologist on the basis of measurement. The subjecti ve assessment of stenosis produced false-positive rates (for assessing stenosis of less than 70% as severe) ranging from 5% among the neuror adiologists to 16% among the radiologists. The false-negative rates (f or assessing stenosis of 70% or more as less than severe) ranged from 12% to 22%. Therefore, a subjective rating of carotid stenosis may lea d to erroneous estimation of the severity of disease. This problem has therapeutic implications, because carotid endarterectomy has been sho wn to benefit only patients with stenosis of greater than 70%, as asse ssed according to strict measurement guidelines.