Pitfalls in the preoperative evaluation of subarachnoid hemorrhage without digital subtraction angiography: report on 2 cases

BACKGROUND: Digital subtraction angiography has been used in the diagnosis of aneurysmal SAH and as a preoperative imaging method. However, new methods such as MRA and CTA are now deemed by many institutions to provide sufficient information to allow surgery to go ahead without a preliminary DSA scan. We report on 2 cases of SAH in which there were additional lesions that were difficult to evaluate because of the lack of DSA information. CASE DESCRIPTIONS: The fist patient demonstrated SAH with IVH. Computed tomographic angiography revealed an ACoA aneurysm with a bleb. We first thought that the SAH and IVH were both caused by a ruptured ACoA aneurysm but noted that hemorrhage pattern was inconsistent with the location and orientation of the aneurysm. A DSA scan revealed a dural arteriovenous fistula in the region of the craniocervical junction, supplied by the right occipital artery. We surmised that the SAH and IVH were caused by a large varix of DAVF and that the ACoA aneurysm would be unruptured. The second patient presented with a 1-week history of headaches and nausea and was diagnosed to have an SAH caused by a ruptured MCA aneurysm. We suspected vasospasm in the second portion of the MCA on CTA, but could not precisely evaluate the affected lesions. A diffusion-weighted MRI scan 4 days after surgery revealed a high-intensity area in the region of the right MCA. The MCA had already seemed to be affected at admission because vasospasm rarely develops within 4 days of the onset of SAH. CONCLUSIONS: As long as the CTA scan is of adequate quality and shows the aneurysm clearly, we consider that an additional DSA provides little useful information for surgery. However, in such cases, the information from a DSA scan is needed for the evaluation of secondary factors that are not directly associated with the aneurysm.