The role of MR angiography in the pretreatment assessment of intracranial aneurysms: A comparative study

BACKGROUND AND PURPOSE: With developments in coil technology, intracranial aneurysms are being treated increasingly by the endovascular route. Endovas cular treatment of aneurysms requires an accurate depiction of the aneurysm neck and its relation to parent and branch vessels preoperatively. Our goa l was to estimate the clinical efficacy of MR angiography (MRA) in the pret reatment assessment of ruptured and unruptured intracranial aneurysms. We c ompared MRA source data (axial acquired partitions), multiplanar reconstruc tion (MPR) of these data, as well as maximum intensity projection (MIP) and 3D-isosurface images with intraarterial digital subtraction angiography (I A-DSA). METHODS: The study was performed in 29 patients with 42 intracerebral aneur ysms. The MRA data mere examined in four different forms-as axial source da ta, MPR images of the source data, and MIP and 3D isosurface-rendered image s. A composite standard of reference for each aneurysm was then constructed using this information together with the HA-DSA findings by looking at ane urysm detection rate, aneurysm morphology, neck interpretation, and branch vessel relationship to the aneurysm. All techniques, including conventional IA-DSA, were then scored independently on a five-point scale from 1 (non d iagnostic) to 5 (excellent correlation with the standard of reference) for each of the aneurysm components as compared with the composite picture. An overall score for each technique was also obtained. RESULTS: Of the 42 aneurysms examined, 34 mere small (<10 mm), six mere lar ge (10-25 mm), and two were giant (>25 mm). Three aneurysms were not detect ed with MRA. These were smaller than 3 mm and either in an anatomically dif ficult location (middle cerebral artery bifurcation) or obscured by adjacen t hematoma. Two large aneurysms were depicted as undersized by IA-DSA owing to the presence of intramural thrombus shown by MRA axial source data. IA- DSA received the highest scores overall and in three of the four subgroups. Three-dimensional isosurface reconstructions scored higher than did IA-DSA for depiction of the aneurysm neck, although this difference was not signi ficant. The MPR and 3D-isosurface images mere comparable to those of IA-DSA in all categories. MPR images were particularly useful for defining branch vessels and the aneurysm neck. MIP images scored poorly in all subgroups ( P < .005) compared with IA-DSA findings, except for in aneurysm detection. Source data images were significantly inferior to those of IA-DSA in all ca tegories (P < .005). CONCLUSION: MRA is currently inferior to IA-DSA in pretreatment assessment of intracranial aneurysms, and can miss small lesions (<3 mm). It can, howe ver, provide complementary information to IA-DSA, particularly in anatomica lly complex areas or in the presence of intramural thrombus. If MRA is used in aneurysm assessment, a meticulous technique with reference to both axia l source data and MPR is mandatory. The axial source data should not be int erpreted in isolation. Three-dimensional isosurface images are comparable t o those of IA-DSA and are more reliable than are MIP images, which should b e interpreted with caution.