A standardized method for measuring intracranial arterial stenosis

BACKGROUND AND PURPOSE: Atherosclerosis of the major intracranial arteries is an important cause of ischemic stroke. We established measurement criter ia to assess percent stenosis of a major intracranial artery (carotid, midd le cerebral, vertebral, basilar) and determined the interobserver/intraobse rver agreements and interclass/intraclass correlations of these measurement s, METHODS: We defined percent stenosis of an intracranial artery as follows: percent stenosis = [(1 - (D-stenosis/D-normal))] x 100, where D-stenosis = the diameter of the artery at the site of the most severe stenosis and D-no rmal = the diameter of the proximal normal artery. If the proximal segment was diseased, contingency sites were chosen to measure D-normal: distal art ery (second choice), feeding artery (third choice). Using a hand-held digit al caliper, three neuroradiologists independently measured D-stenosis and D -normal of 24 stenotic intracranial arteries. Each observer repeated the re adings 4 weeks later, We determined how frequently two observers' measureme nts of percent stenosis of each of the 24 diseased arteries differed by 10% or less. RESULTS: Among the three pairs of observers, interobserver agreements were 88% (observer 1 versus observer 2), 79% (observer 1 versus observer 3), 75% (observer 2 versus observer 3) for the first reading and were 75% (observe r 1 versus observer 2), 100% (observer 1 versus observer 3), and 71% (obser ver 2 versus observer 3) for the second reading. Intraobserver agreement fo r each of the observers was 88%, 83%, and 100%, Interclass correlation was 85% (first reading) and 87% (second reading). Intraclass correlation was 92 % (first and second readings combined). CONCLUSION: This method shows good interobserver and intraobserver agreemen ts for the measurement of intracranial stenosis of a major artery. If valid ated in subsequent studies, this method may serve as a standard for the mea surement of percent stenosis of an intracranial artery.