Small, patent cerebral aneurysms: atypical appearances at 1.5-T MR imaging.

Abstract

To determine the frequency and characteristics of small cerebral aneurysms with atypical appearances on magnetic resonance (MR) images. MR imaging studies (n = 117) obtained at 1.5 T of small aneurysms (< 1 cm diameter) were prospectively and retrospectively analyzed. Signal intensity characteristics and gadolinium-enhancement patterns in 84 aneurysms (62 patients) were evaluated. The patency of all aneurysms was confirmed at angiography or at the time of surgery. A characteristic signal void was seen on 62 (53%) of 117 studies. On the remaining 55 (47%) studies, aneurysms had atypical signal intensity that was isointense, heterogeneous, or hyperintense. Contrast-enhanced aneurysms were seen on 27 (53%) of 51 gadolinium-enhanced studies. Atypical MR imaging characteristics were seen in roughly half of cases. These atypical-appearing aneurysms may erroneously be considered to be thrombosed or be mistaken for other common lesions such as small tumors and be dismissed as nonvascular.