SMALL, PATENT CEREBRAL ANEURYSMS - ATYPICAL APPEARANCES AT 1.5-T MR-IMAGING

PURPOSE: To determine the frequency and characteristics of small cereb ral aneurysms with atypical appearances on magnetic resonance (MR) ima ges. MATERIALS AND METHODS: MR imaging studies (n = 117) obtained at 1 .5 T of small aneurysms (<1 cm diameter) were prospectively and retros pectively analyzed. Signal intensity characteristics and gadolinium-en hancement patterns in 84 aneurysms (62 patients) were evaluated. The p atency of all aneuryms was confirmed at angiography or at the time of surgery. RESULTS: A characteristic signal void was seen on 62 (53%) of 117 studies. On the remaining 55 (47%) studies, aneurysms had atypica l signal intensity that was isointense, heterogeneous, or hyperintense . Contrast-enhanced aneurysms were seen on 27 (53%) of 51 gadolinium-e nhanced studies. CONCLUSION: Atypical MR imaging characteristics were seen in roughly half of cases. These atypical-appearing aneuryms may e rroneously be considered to be thrombosed or be mistaken for other com mon lesions such as small tumours and be dismissed as nonvascular.