Clinicopathological study of intracranial fusiform and dolichoectatic aneurysms - Insight on the mechanism of growth

Background and Purpose-Intracranial fusiform aneurysms can be divided into 2 clinically different subtypes: acute dissecting aneurysms and chronic fus iform or dolichoectatic aneurysms. Of these 2, the natural history and grow th mechanism of chronic fusiform aneurysms remains unknown. Methods-A consecutive series of 16 patients with chronic fusiform aneurysms was studied retrospectively to clarify patient clinical and neuroradiologi cal features. Aneurysm tissues were obtained from 8 cases and were examined to identify histological features that could correspond to the radiologica l findings. Results-Four histological features were found: (1) fragmentation of interna l elastic lamina (TEL), (2) neoangiogenesis within the thickened intima, (3 ) intramural hemorrhage (IMH) and thrombus formation, and (4) repetitive in tramural hemorrhages from the newly formed vessels within thrombus. IEL fra gmentation was found in all cases, which suggests that this change may be o ne of the earliest processes of aneurysm formation. MRI or CT detected IMH, and marked contrast enhancement of the inside of the aneurysm wall (CEI) o n MRI: corresponded well with intimal thickening. Eight of 9 symptomatic ca ses but none of 7 asymptomatic cases presented with both radiological featu res. Conclusions-Data suggest that chronic fusiform aneurysms are progressive le sions that start with TEL fragmentation. Formation of IMH seems to be a cri tical event necessary for lesions to become symptomatic and progress, and t his can be monitored on MRI. Knowledge of this possible mechanism of progre ssion and corresponding MRI characteristics could help determine timing of surgical intervention.