Background: Along with clinical introduction of non-invasive imaging modalities in daily practice, intramural hematoma (IMH) has been successfully incorporated as a disease entity of acute aortic syndrome (AAS). However, clinical outcome data are limited to determine whether IMH is a just precursor of classic aortic dissection (AD).
Methods and Results: Clinical data of consecutive patients with AAS registered between 1994 and 2015 were analyzed. A total of 1,012 patients (mean age, 59.2 ± 13.7 years; 557 men [55.0%]) were enrolled, which included 671 with AD (66.3%) and 341 with IMH. Type A AD was the most common (n = 395, 39.0%), followed by type B AD (n = 276, 27.3%), type B IMH (n = 200, 19.8%), and type A IMH (n = 141, 13.9%). Patients with AD were younger than those with IMH (56.4±14.1 vs. 64.6±11.3 years, p<0.001). Patients with AD showed more frequent involvement of the ascending aorta (59.0% vs. 40.8%, p<0.001), whereas those with IMH showed higher frequency of distal aorta involvement (40.8% vs. 59.2%, p<0.001). Surgical intervention was performed more frequently in patient with AD than in those with IMH (61.1% vs. 16.7%, p<0.001). The frequency of surgery was significantly higher in patients with type A AD than in those with type A IMH (90.7% vs. 37.4%, p <0.001). Overall in-hospital mortality was 8.6% (87/1,012), and mortality rate showed marked variation according to the underlying disease entity: it was the highest in patients with type A AD (14.9%), followed by type A IMH (7.8%), type B AD (5.1%), and type B IMH (1.9%, p<0.001). The 3-year survival rate was the highest in type B IMH (92.1 ± 2.0%), followed by type A IMH (87.7 ± 2.8%), type B AD (85.5 ± 2.2%), and type A AD (77.3 ± 2.1%, p <0.001).
Conclusions: IMH comprised significant proportion of patients with AAS and showed different clinical features and outcomes compared to classic AD. These findings suggest that IMH should be regarded as an independent disease entity, not just a precursor of classic AD.