SEASONAL AND LATITUDINAL OCCURRENCE OF CEREBRAL VASOSPASM AND SUBARACHNOID HEMORRHAGE IN THE NORTHERN-HEMISPHERE

Using patient data obtained from the International Cooperative Aneurys m Study that evaluated clinical records from 68 neurosurgical centers in 14 countries, we evaluated the data as to the monthly occurrence of cerebral vasospasm and subarachnoid hemorrhage relative to the latitu de of the medical center where the data were gathered. Using the Edwar ds analysis for cyclic patterns, we examined peak to trough ratios and months of peak to assess the strength and nature of the cyclic variat ions between December 1980 and July 1983. Of the 3,521 subarachnoid he morrhage patient records examined, 685 developed some grade of vasospa sm as defined symptomatically, angiographically, and by the Fisher Gra ding Scale. Cyclic analysis demonstrated a strong seasonal occurrence for the incidence of subarachnoid hemorrhage, with a peak in February, in the northern hemisphere. Cerebral vasospasm incidence, after contr olling for subarachnoid hemorrhage occurrence, exhibited only a small peak to trough ratio (1.15) relative to the larger ratio (1.74) seen w ith unadjusted vasospasm data. Age was related to both incidence and l ocation. In populations at. high risk for cerebrovascular diseases, cl imatic conditions may act as syn chronizers of pathologic vascular eve nts.