Within the spectrum of acute aortic syndromes, intramural hematoma (IMH) is a 
distinct lesion that is characterized by crescentic or circumferential 
thickening of the aortic wall in the absence of an intimal defect. The reported 
incidence of IMH among all type A acute aortic syndromes ranges from 3.5% to 
28.3%. As compared with acute aortic dissection, IMH is a disease of the 
elderly, and it tends to have reduced rates of malperfusion syndromes, aortic 
insufficiency, and root dilation, yet also tends to have increased rates of 
pericardial effusion, cardiac tamponade, and periaortic hematoma. With respect 
to natural history, IMH may progress to classic dissection, frank rupture, or 
aneurysmal dilation; yet, IMH may also regress and be completely resorbed. 
However, studies disagree over the rates of progression or regression; as such, 
few studies agree on the short-term and long-term prognosis associated with IMH. 
American and European guidelines advocate emergent surgery for all acutely 
presenting type A IMH. At a minimum, supracoronary replacement of the aorta with 
hemiarch reconstruction is the preferred extent of operative repair to reduce 
rates of long-term reintervention for disease progression. However, valve and/or 
root procedures may be necessary proximally, while total arch reconstruction or 
hybrid procedures for the descending aorta may be necessary distally. Much 
remains unknown for IMH, including the ideal extent of aortic repair, 
risk-stratification for elderly patients, and the optimal treatment paradigm for 
stable, uncomplicated IMH. As such, IMH remains a diagnostic and therapeutic 
challenge for the cardiovascular surgeon.