Background: The natural history of type B intramural hematomas is little-known. Aneurysmal progression or an aortic dissection occurs in 15 to 20% of the cases. The study of the natural anatomical evolution could help identify the patients at risk of unfavorable evolution. Methods: All the patients monitored for a type B intramural hematoma between 2009 and 2018 were included in this monocentric retrospective study. Computed tomography angiography centerline measurement of diameters was obtained in various points of aortic segmentation on day (D) 0 and at one month (M1). Aortic volumes (lumen, intramural hematoma, and total volume) were calculated. The circulating volume was calculated using the volume rendering method. The volume of the intramural hematoma was measured using a manual section-by-section segmentation tool, and the total volume was obtained by summing up the two preceding volumes. Two groups of patients were compared: group 1 (favorable anatomical evolution) and group 2 (unfavorable anatomical evolution). Results: Between January 2008 and August 2018, 25 patients were managed for a type B intramural hematoma in our center. After an average follow-up of 15.5 months (1-52), 13 patients (52%) presented a favorable evolution and 12 (48%) an unfavorable evolution. At M1, a significant increase of the luminal diameters (37 mm vs. 32 mm; P < 0.01) and a significant reduction in the longitudinal extension (19 mm vs. 26 mm; P < 0.01) were observed. The maximum aortic diameter evolved significantly between D0 and M1 in the unfavorable evolution group (49 mm vs. 44 mm, respectively; P = 0.038). Such a difference was not found in the favorable evolution group (37.4 vs. 37.1, respectively; P = 0.552). An overall significant reduction in the total aortic volume (166 cm3 vs. 219 cm3; P < 0.01), the circulating volume (124 cm3 vs. 145 cm3; P = 0,026), and the volume of the hematoma (42 cm3 vs. 39 cm3; P < 0.01) was observed. The circulating volume decreased significantly between D0 and M1 in the favorable evolution group (110 cm3 vs. 135 cm3; P = 0.05), whereas no difference was noted in the unfavorable group (142 cm3 vs, 157 cm3; P = 0.24). Conclusions: The progression of the maximum aortic diameter and of the circulating volume after one month of follow-up could be predictive factors of the poor long-term evolution of type B intramural hematomas.