BACKGROUND: Aortic intramural hematoma (IMH) evolves very dynamically in the 
short-term to regression, dissection, or aortic rupture. The aim of the present 
study was to assess the long-term clinical and morphological evolution of 
medically treated IMH.
METHODS AND RESULTS: Fifty of 68 consecutive patients with aortic IMH monitored 
clinically and by imaging techniques at 3, 6, and 12 months and annually 
thereafter were prospectively studied. Mean follow-up was 45+/-31 months. In the 
first 6 months, total IMH regression was observed in 14 and progression to 
aortic dissection in 18 patients; in 14 of these, the dissection was localized, 
and 12 later developed pseudoaneurysm. At the end of follow-up, the IMH had 
regressed completely without dilatation in 17 patients (34%), progressed to 
classical dissection in 6 (12%), evolved to fusiform aneurysm in 11 (22%), 
evolved to saccular aneurysm in 4 (8%), and evolved to pseudoaneurysm in 12 
(24%). Evolution to dissection was related to echolucency (P<0.02) and to 
longitudinal extension of IMH (P<0.01). Multivariate analysis showed an 
independent association between regression and smaller maximum aortic diameter 
and between aneurysm formation and atherosclerotic ulcerated plaque and absence 
of echolucent areas in IMH.
CONCLUSIONS: The most frequent long-term evolution of IMH is to aortic aneurysm 
or pseudoaneurysm. Complete regression without changes in aorta size is observed 
in one third of cases, and progression to classical dissection is less common. A 
normal aortic diameter in the acute phase is the best predictor of IMH 
regression without complications, and absence of echolucent areas and 
atherosclerotic ulcerated plaque are associated with evolution to aortic 
aneurysm.