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 criteria to assess percent stenosis of a major intracranial artery (carotid, middle cerebral, vertebral, basilar) and determined the interobserver/intraobserver agreements and interclass/intraclass correlations of these measurements. 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(normal) = the diameter of the proximal normal artery. If the proximal segment was diseased, contingency sites were chosen to measure D(normal): distal artery (second choice), feeding artery (third choice). Using a hand-held digital caliper, three neuroradiologists independently measured D(stenosis) and D(normal) of 24 stenotic intracranial arteries. Each observer repeated the readings 4 weeks later. We determined how frequently two observers' measurements 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% (observer 1 versus observer 2), 100% (observer 1 versus observer 3), and 71% (observer 2 versus observer 3) for the second reading. Intraobserver agreement for 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 agreements for the measurement of intracranial stenosis of a major artery. If validated in subsequent studies, this method may serve as a standard for the measurement of percent stenosis of an intracranial artery.