Although the same treatment strategy has been applied for patients with aortic intramural hematoma (AIH) as typical aortic dissection (AD), the natural history of AIH with medical treatment is not known clearly. The purposes of this study were to test the hypothesis that absence of direct flow communication through intimal tear in AIH has different impact on clinical course compared with typical AD and to clarify the natural history of AIH.

Total 181 patients of acute aortic pathology (AD / AIH=57 / 124) were enrolled from 5 institutions. Patients received medical treatment without surgical intervention regardless of the affected site in acute stage, and follow-up imaging studies (FUIS) were performed in 105 patients with AIH. Clinical data of these patients were retrospectively analyzed.

Fifty-four patients showed involvement of the ascending aorta (AD / AIH=13 / 41) and 127 revealed distal pathology (AD / AIH=44 / 83). Compared to the patients with AD, those with AIH were older regardless of the type and showed higher incidence of pleural effusion and mediastinal hemorrhage. In-hospital mortality of proximal AIH was 7 %, which was significantly lower than that of proximal AD (62 %); mortality of distal AIH was also lower than that of distal AD (1.2 Vs 9 %, p < 0.05). In proximal AIH, FUIS confirmed resorption of AIH in 67 %(24/36) and development of AD in 25 %(9/36). In distal AIH, resorption was confirmed in 78 %(54/69) and development of AD in 16 %(11/69).

Patients with AIH showed excellent clinical course and high rate of resorption with medical treatment regardless of the affected site; typical AD developed only in limited cases. Absence of direct flow communication through intimal tear in AIH might explain more favorable response to medical treatment than typical AD.