Location of the False Lumen Within the Medial Layer in Acute Intramural Hematoma.

Background: We compared the location of the false lumen within the medial layer between acute intramural hematoma (AIH) and acute aortic dissection (AAD) using microscopic images of aortic specimens and examined the associations with patient characteristics, CT findings, and late outcomes.

Methods and results: Among 293 patients undergoing surgery for Stanford type A acute aortic syndrome between 2008 and 2018, 45 patients had neither an identifiable intimal tear, flow to the false lumen on preoperative CT or intimal tear by intraoperative observation (AIH group), and 98 patients with patent false lumen were enrolled (AAD group). The AIH group had a significantly thinner outer media thickness (OMT) than the AAD group. The AIH group showed more pericardial effusion, but distal progression of dissection and branch vessel involvement were limited. The change in aortic diameter after surgery was insignificant in the AIH group, whereas in the AAD group it continued to increase. Cumulative incidence of aortic adverse events was significantly higher among AAD patients, but no significant difference was observed in survival between groups.

Conclusions: The AIH group had a significantly thinner OMT than the AAD group, which was significantly associated with a large amount of pericardial effusion, greater false lumen diameter, and limited progression of aortic dissection.