Filling defect sign in CT diagnosis of ruptured aneurysm.

We have encountered a ruptured aneurysm as a filling defect in cisternal blood on CT in patients with acute subarachnoid haemorrhage (SAH), as high-attenuation blood can act as a contrast medium. We term this finding the "filling defect sign". To evaluate the usefulness of the sign in the diagnosis of a ruptured aneurysm, we retrospectively analysed CT with 10-mm-thick slices obtained within 2 days of onset of SAH in 100 consecutive patients. The sign was observed in 30 of the 100 patients, and in 13 (68%) of 19 patients with a ruptured aneurysm more than 10 mm in diameter. The filling defect sign is useful in predicting the site of rupture.