The differences and similarities between intramural hematoma of the descending aorta and acute type B dissection

Aortic intramural hematoma type B (IMHB) is a variant of acute aortic syndrome, which presents with symptoms similar to classic type B aortic dissection (ABAD). However, the natural history of IMHB is not well understood. The purpose of this study was to better characterize IMHB, comparing its clinical characteristics, treatment, and in-hospital and long-term outcomes to those with classic ABAD.

A total of 107 IMHB and 790 ABAD patients enrolled in the International Registry of Acute Aortic Dissection (IRAD) between January 1996 and June 2012 were analyzed. Accordingly, differences in presentation, diagnostics, therapeutic management, and outcomes were assessed.

As compared with the ABAD, IMHB presented predominantly in males (62% vs 33%; P < .001) at older age (69 ± 12 vs 63 ± 14; P < .001). IMHB patients more often had chest pain (80% vs 69%; P = .020) and periaortic hematoma (22% vs 13%; P = .020) and were more often treated medically (88% vs 62%; P < .001), with surgical/endovascular interventions being reserved for more complicated patients. Overall in-hospital mortality was 10% (IMHB, 7% vs ABAD, 11%; P = NS). Six out of seven IMHB deaths occurred during medical treatment, two due to aortic rupture. During follow-up in IMHB, patient mortality was 7%, and no adverse events, including progression to an aortic dissection or aortic rupture, were observed. Imaging showed significantly more aortic enlargement at the level of the descending aorta in ABAD patients (39% vs 61%; P = .034).

Most IMHB patients can be treated medically, and aortic enlargement is less common during follow-up, which may suggest that IMHB may have a slightly more benign course compared with classic ABAD in the acute setting.