EVALUATION OF THE CIRCLE OF WILLIS WITH 3-DIMENSIONAL CT ANGIOGRAPHY IN PATIENTS WITH SUSPECTED INTRACRANIAL ANEURYSMS

PURPOSE: To determine the usefulness of CT angiography in the setting of suspected acute subarachnoid hemorrhage or intracranial aneurysm. M ETHODS: We prospectively studied 68 patients suspected of having subar achnoid hemorrhage or an intracranial aneurysm with noncontrast CT of the head followed immediately by contrast-enhanced helical CT of the c ircle of Willis with three-dimensional reconstruction. Twenty-seven pa tients with CT findings positive for subarachnoid hemorrhage or intrac ranial aneurysm were evaluated with digital subtraction angiography or MR angiography within 12 hours of CT angiography. Patients with negat ive CT/CT angiography findings were followed up with lumbar puncture. RESULTS: CT angiography showed 23 of 24 aneurysms and 2 of 2 arteriove nous malformations (sensitivity, 96%; specificity, 100%). Aneurysm siz e ranged from 2 to 40 mm (mean, 7.9 mm). Interobserver variability was 10%. In the 23 cases of subarachnoid hemorrhage, cisternal blood did not limit the three-dimensional reconstruction. Two patients with aneu rysms on CT angiography had normal noncontrast scans. CONCLUSIONS: CT angiography of the circle of Willis is a useful technique for evaluati on of suspected acute subarachnoid hemorrhage and intracranial aneurys m. It provides anatomic display of intracranial aneurysms, allowing fo r planning of conventional angiography and surgical approach. In selec ted cases, CT angiography may eliminate the need for preoperative conv entional angiography.