Emerging Concepts in Intramural Hematoma Imaging

Intramural hematoma (IMH) is included in the spectrum of acute aortic syndrome and appears as an area of hyperattenuating crescentic thickening in the aortic wall that is best seen at nonenhanced computed tomography. IMH is historically believed to originate from ruptured vasa vasorum in the aortic media without an intimal tear, but there are reports of small intimomedial tears identified prospectively at imaging or found at surgery in some cases of IMH. These reports have blurred the distinction between aortic dissection and IMH and raise questions about what truly distinguishes the entities that compose acute aortic syndrome. The pathophysiology of these subgroups and the controversies surrounding their differentiation are discussed. The natural history of IMH is highly variable; it may resolve or progress to aneurysm, dissection, or rupture. The authors review various imaging prognostic factors that should be reported by the radiologist, including Stanford classification, maximum aortic diameter, maximum IMH thickness, focal contrast enhancement (including ulcerlike projection and intramural blood pool), and pleural or pericardial effusion. Medical (nonsurgical) versus surgical treatment strategies depend primarily on the Stanford classification, although more recent studies of Asian cohorts report success of initial medical treatment in patients with Stanford type A IMH, with timed (delayed) surgery for patients who develop complications. Understanding the imaging appearance and prognostic factors of IMH helps the radiologist and surgeon identify patients at greatest risk for complications to ensure appropriate treatment and improve patient outcomes. (C) RSNA, 2016