The relation of cerebral vasospasm to the extent and location of subarachnoid blood visualized by CT scan: a prospective study.

In 41 cases of verified ruptured saccular aneurysm, we prospectively predicted the presence or absence of delayed symptomatic cerebral vasospasm. CT criteria quantifying the extent and location of subarachnoid blood (developed in our previous retrospective study) were used in this prospective series of patients. Twenty-two patients had recognizable subarachnoid clots larger than 3 X 5 mm or layers of blood more than 1 mm thick (measured on reproduced images). In 20 of the 22 patients with severe significant clot or thick layer, severe vasospasm was correctly predicted and localized (2 false positives). In 19 patients with no blood, or diffuse blood, or blood outside the subarachnoid space, the absence of severe vasospasm was correctly predicted in 14 (5 false negatives). All of the false-positive and false-negative cases could be explained by inadequate CT technique. The data indicate that the extent and location of blood in the subarachnoid space determine the severity and location of vasospasm and that patients in jeopardy of developing symptomatic cerebral vasospasm can now be identified. Early preventive measures may now be assessed more accurately.