Natural History and Long-Term Outcomes of Medically Managed Type B Intramural Hematoma

Type B intramural hematoma (IMH) if often managed medically yet may progress to dissection, aneurysmal dilation, or rupture. The aim of this study was to report the natural history of medically managed type B IMH and factors associated with progression. We reviewed patients with medically managed type B IMH between January 1995 and December 2022 at a single center. Any patients with immediate surgical or endovascular intervention were excluded. Demographic profiles, comorbidities, imaging, and follow-up details were reviewed. Patients were divided into two groups: group 1 had isolated IMH and group 2 had IMH along with aneurysm or dissection at the time of presentation. On follow-up, progression was defined as degeneration to aneurysm/dissection or an increase in the thickness of IMH in group 1. In group 2, progression was an increase in the size of aneurysm or development of new dissection. Of 104 patients with type B IMH during the study period, 92 were medically managed. The median age was 77 years, and 45 (48.9%) were female. Comorbidities included hypertension (83.7%), hypercholesterolemia (44.6%), and active smoking (47.8%). The mean SVS comorbidity score was 6.3. The mean IMH thickness and aortic diameter at presentation were 8.9 mm and 38.3 mm, respectively. The median follow-up was 55 months. Overall survival at 1 year and 5 years was 85.8% and 61.9%, respectively. During follow-up, 19 patients (20.7%) required intervention, more common in group 2 (8/66, 12.3% group 1 vs 11/26, 42.3% group 2, P = .001). This resulted in higher freedom from intervention in group 1 at 1 year (93.5% vs 62.7%) and 5 years (87.5% vs 51.1%, P < .001, Fig 1). Indication for intervention was dissection (N = 4), aneurysm (N = 12), and progression of IMH (N = 3). In group 1, progression was seen in 25 (37.9%), 3 (4.5%) remained stable, 29 (43.9%) had complete resolution of IMH, and nine patients were lost to follow-up (Fig 2). In group 2, 11 (42.3%) patients had progression, 7 (26.9%) remained stable, and eight were lost to follow-up. In group 1, IMH thickness at presentation >7.2 mm is associated with increased odds of progression (odds ratio = 6.01, 95% confidence interval = 1.9-22.3) and intervention (odds ratio = 6.6, 95% confidence interval = 1.1-130) during the follow-up. Although many patients with type B IMH managed medically stabilize or regress, progression or need for intervention can occur in up to 40% of cases. This is associated with the presence of aneurysm, dissection, and IMH thickness. Long-term follow-up is mandatory as late interventions occur, particularly for higher risk patients.