破裂および未破裂脳動脈瘤のMRA診断

Abstract

Most previous reports have explored the efficacy of magnetic resonance angiography (MRA) as a noninvasive screening method for the detection of unruptured intracranial aneurysms and occlusive vascular disease. The purpose of this study was to assess the accuracy of three-dimensional (3D) time-of-flight (TOF) MRA in the identification of ruptured aneurysms presenting subarachnoid hemorrhage (SAH) as well as unruptured aneurysms. Sixty-two consecutive patients with 36 ruptured and 32 unruptured aneurysms were examined. MR angiograms and conventional contrast angiograms were retrospectively reviewed with regard to the relation between the detectability on MRA and size of aneurysm, location, and influence of subarachnoid hematoma. The size of ruptured aneurysms was significantly larger than that of unruptured aneurysms. Twenty-seven of 29 ruptured aneurysms in acute stage (93%) was detected on MRA, whereas 29 of 36 unruptured aneurysms (81%) and none of 4 ruptured aneurysms in subacute stage (0%) were detectable. Individual vessel visualization and image quality of MRA in patients with acute SAH were satisfactory, although in patients with subacute SAH, MRA showed poor visualization of vessels due to T1-shortening of subacute surrounding hematoma and presence of delayed vasospasm. Main causes of failure to detect aneurysms on MRA included limitation of spatial resolution, limited projections obtainable with maximum-intensity-projection (MIP) techniques and subacute hematoma simulating flow signal on MIP reconstructions. Improvement of present limitation of MRA requires higher spatial resolution, higher contrast resolution and a more adequate reconstruction method. MRA was considered to be a safe and useful examination for intracranial aneurysms especially in patients with acute SAH.