CT Analysis of the Growth Rate of Aortic Diameter Affected by Acute Type B Intramural Hematoma

Abstract

OBJECTIVE: The purpose of this study was to evaluate the growth rate of aortic diameter affected by acute type B intramural hematoma and the factors that influence its enlargement. MATERIALS AND METHODS: Fifty-four patients were entered into this study, and regular follow-up CT studies (mean +/- SD, 46.9 +/- 27.2 months; range, 5-136 months) were performed. The affected aortas and iliac arteries were divided into five segments. A total of 127 segments were evaluated (aortic arch, n = 47; descending thoracic aorta, n = 51; suprarenal abdominal aorta, n = 24; infrarenal abdominal aorta, n = 3; and iliac artery, n = 2). The growth rate of each segment was obtained on CT. The factors influencing increase in the diameter and growth rate--age, sex, diabetes mellitus, atherosclerotic disease, history of smoking 20 years, chronic renal failure, blood pressure, initial diameter of the lumen, the presence of blood flow in the false lumen--were evaluated by univariate analysis and a multivariate logistic regression model. RESULTS: Twenty (37.0%) of 54 patients had one or more segments that increased in size during the follow-up period. Of a total of 127 segments, 35 (27.6%) increased in size, and for all, the mean growth rate was -0.5 +/- 2.9 mm/year. This negative growth rate represents shrinkage. The mean growth rates within the first year and after 1 year from onset were -2.2 +/- 5.7 and 0.4 +/- 3.2 mm/year, respectively, and a significant difference was observed between them (p < 0.0001). An initial diameter of 40 mm or greater and the presence of blood flow in the false lumen were significant risk factors for an increase in the diameter, as confirmed by univariate and multivariate analyses. CONCLUSION: In patients with type B intramural hematoma, the affected aortas did not show a high incidence of enlargement during the follow-up period, but the affected aortas tended to increase in size after 1 year from onset. An initial diameter of 40 mm or greater and the presence of blood flow in the false lumen were important risk factors for enlargement during the follow-up period.