Figure 2b. Aneurysm in a 78-year-old woman with subarachnoid hemorrhage (Hunt and Hess grade II). (a) Coronal MIP image from multi-detector row CT angiography shows bilobed anterior communicating artery aneurysm (arrows), absent right A1 segment of the anterior cerebral artery, and enlarged left A1 segment (arrowheads). The hyperattenuating tubular structure is a ventriculostomy catheter. (b) Frontal projection from DSA performed with contrast material injection into the right common carotid artery does not depict aneurysm. (c) Frontal projection from DSA performed with contrast material injection into the left common carotid artery depicts the same aneurysm as in a (arrow). The bilobed structure of the aneurysm is not as visible in the frontal view, but note the contrast material filling in both the right and the left A2 segments (arrowheads).