Quantifying unruptured giant intracranial aneurysms by measuring diameter and volume—a comparative analysis of 69 cases

Background: Intracranial aneurysms (IA) are usually quantified according to their largest diameter. However, volumetry has recently been increasingly conducted as well, especially in giant intracranial aneurysms (GIAs). Since so far the true value of GIA volumetry is unknown, we designed a trial to examine correlations between GIA diameter and volume with special focus on clinical implications.Methods: Magnetic resonance imaging of 69 unruptured GIAs in 66 patients was retrospectively evaluated. The largest diameter and volume were measured. Also, potential associations to the patients’ clinical conditions were examined.Results: Comparing GIA sizes of our patient cohort produced different results depending on whether GIA diameter or volume was measured. Measuring the diameter identified posterior circulation GIAs as the largest ones (39.2 mm, IQR 37.3–48.3), while measuring the volume found GIAs of the MCA to be the largest ones (12.3 cm3, IQR 7.2–27.8). A correlation of GIA diameter and volume was only found in anterior circulation GIAs, which were predominantly saccular in shape, but not in those of the posterior circulation, of which most were fusiform. Neither GIA diameter nor GIA volume but only GIA location was associated with neurological deficits.Conclusion: Diameter and volume measurements are not interchangeable modes of GIA quantification. Our data suggest that the idea of distinguishing different sizes of GIA may be clinically less relevant than examining their location, shape or mass effect.