Detection of cerebral aneurysms in nonenhanced CT images of patients with subarachnoid hemorrhage using the filling defect sign

<b>Purpose:</b> Non- traumatic subarachnoid hemorrhage (SAH) constitutes a life-threatening event, which is caused in 85% by ruptured aneurysms. Identifying those aneurysms as the bleeding cause is essential for further therapy. This study explores whether relatively hypodense sparing of aneurysms in the blood-filled subarachnoid space (filling defect sign = FD) on nonenhanced CT scans (NECT) can help estimate aneurysm location and size. <b>Methods:</b> NECT of fifty patients with aneurysmal SAH, who were also examined with a catheter angiography, were retrospectively analyzed by three neuroradiologically experienced radiologists. They rated the aneurysm location and size by applying the FD. Logistic regression analysis was performed to determine if a correlation between aneurysm location, aneurysm size, Fisher score and the detectability of a FD exists. For quantitative analysis the average densities of the aneurysm were compared to that of surrounding structures. <b>Results:</b> In 75% of the cases, the aneurysm was identified correctly by using the FD. The highest detection rate was given for MCA (90%) and BA aneurysms (90%). Aneurysm location (<i>p</i> = .019), size (<i>p</i> = .020), and the Fisher score (<i>p</i> = .008) significantly influenced aneurysm detection using the FD. The aneurysm size measured in correctly identified aneurysms correlated significantly with the sizes measured in the catheter angiography (<i>p</i> < .001). A cut-off point of 51 HU could be determined to distinguish aneurysm from surrounding SAH with a specificity of 92% and a sensitivity of 86%. <b>Conclusions:</b> In three-fourths aneurysm location and size can be determined on NECT using the FD. An additional quantitative analysis can support the diagnosis with a high specificity and sensitivity.