The natural history of isolated carotid siphon stenosis.

Between August 1978 and July 1983, 93 patients (71 with unilateral and 22 with bilateral isolated carotid siphon stenosis) were identified from a review of 885 consecutive cerebral arteriograms. This yielded 115 cerebral hemispheres at risk. At the time of arteriography, 93 hemispheres were asymptomatic regarding the hemisphere with siphon stenosis (group I), whereas 22 hemispheres in 22 patients had had neurologic events referable to the hemisphere with siphon stenosis (group II). During follow-up (range 1 to 62 months, mean 22.5 months), 64.5% of initially asymptomatic hemispheres remained asymptomatic, 6.5% experienced transient ischemic attacks (TIAs), and 4.3% developed strokes. During the same follow-up period, 63.6% of initially symptomatic hemispheres became asymptomatic, 9.1% had recurrence of TIAs, and 9.1% developed strokes. Sixteen of 71 group I patients (22.5%) and 5 of 22 group II patients (22.7%) died during follow-up. The overall incidence of nonfatal stroke and TIAs was 6.5% and 8.6%, respectively. Myocardial infarction (MI) and stroke accounted for deaths in 6.5% and 4.3% of patients, respectively. There was no significant difference in the incidence of TIA, stroke, or death between group I and group II. The percentage of siphon stenosis in all patients experiencing stroke or TIA (35.4 +/- 14.4%) was not significantly different from that in patients who remained asymptomatic (32.3 +/- 10.6%). Patients with carotid siphon stenosis are at an increased risk of death, stroke, and TIAs compared with the population at large. However, the risk of stroke is less than the risk of stroke in patients with TIAs assumed to be caused by carotid bifurcation disease.(ABSTRACT TRUNCATED AT 250 WORDS)