PURPOSE: To analyze the CT findings of aortic intramural hematoma (IMH) with or without associated penetrating aortic ulcer (PAUH), as seen on initial and follow-up CT scans. MATERIALS AND METHODS: We retrospectively analyzed the CT findings of 36 cases diagnosed clinically and radiologically as IMH (n=7) and PAUH (n=29) after initial and follow-up CT scanning. The period between initial and follow-up scanning-which was performed between two and four times-ranged from 1 week to 91 months (mean: IMH, 18.4 months;PAUH, 16.2 months). RESULTS: With regard to maximal thickness and extension of IMH, maximal diameter of the involved aorta, inward displacement of intimal calcification, Stanford type of IMH, and pleural and pericardial effusion between IMH & PAUH, the results were not statistically significant, but PAUH tends to develop in older patients and shows a more frequent incidence of aortic atherosclerosis. Only PAUH involved abdominal aortic a-neurysm and focal right renal infarction, each in one case. Penetrating aortic ulcers (PAU) were more frequently found in the proximal descending thoracic aorta (n=24) than in the mid(n=11) to distal(n=10) descending thoracic aorta. Among 53 cases of PAU, seven could not be detected on initial CT scans; this was due to excessive scan thickness (n=4) and masking of the aortic ulcer by IMH(n=3), circumstances which were visualized after resolution of IMH. Follow-up CT scanning showed that PAU progressed to fusiform or saccular aortic dilatation (n=15) or localized aortic dissection (n=4), and that in 34 cases, there was no interval change. Follow-up CT findings of IMH in cases of PAUH were as follows: Type A (n=8), with four resolutions after surgery and four after conservative treatment; Type B (n=21), with 21 resolutions after conservative treatment. Follow-up CT findings of IMH were as follows: Type A (n=2), with one resolution after surgery and one after conservative treatment; Type B (n=5), with progression of typical aortic dissection in two cases, and three resolutions after conservative treatment. CONCLUSION: PAUH is characterized by its occurrence in older patients, a more frequent incidence of aortic atherosclerosis and abdominal aortic aneurysm, but no difference in the extension of IMH and other CT findings between PAUH and IMH. Branch vessel involvement was noted in one case of PAUH but not in cases of IMH. Follow-up CT scanning showed that in the absence of surgery, IMH progressed to aortic dissection or resolution. In all patients who did not undergo surgery, PAU progressed to saccular or fusiform aortic dilatation, localized aortic dissection and no interval change, with resolution of IMH after conservative treatment. Initial and follow-up thin-slice spiral CT scanning can provide correct diagnosis and treatment planning (especially ascending aorta is involved), and permit differentiation between PAUH and IMH.