Type A

Significant controversy exists over natural evolution of type A IMH. The mortality rate of the medically treated groups in European and American series is very high, while in the Asian series it is very low10-12,17,18,32-34. A European multicenter study32 of 66 IMH showed a global mortality rate of 20%. In this study, a high incidence of type A IMH (58%) was observed. Surgery was indicated in 84% of type A cases, and early mortality was 8% with swift surgery versus 55% without surgery. These results suggest that the short-term prognosis is poor in IMH involving the ascending aorta, and surgical repair should be considered. The high risk of "wait and see" in type A IMH, however, is reflected in 55% early mortality with medical treatment compared to 8% with surgical repair (P = 0.004). However, the study was retrospective, and the reasons from four different centers for choosing medical treatment

Figure 14.4. In left images, TEE in transverse (A) and longitudinal (A') views show minimal thickening of the ascending aorta wall, which was not diagnosed as abnormal. B. CMR performed 72 hours latter shows hyperintense signal in ascending aorta wall diagnosed as type AIMH. C. CT performed the same day as CMR discloses a small thickening of the aorta wall. The diagnosis of INH was only considered definitive in the CMR study.

Figure 14.4. In left images, TEE in transverse (A) and longitudinal (A') views show minimal thickening of the ascending aorta wall, which was not diagnosed as abnormal. B. CMR performed 72 hours latter shows hyperintense signal in ascending aorta wall diagnosed as type AIMH. C. CT performed the same day as CMR discloses a small thickening of the aorta wall. The diagnosis of INH was only considered definitive in the CMR study.

were not described. In the IRAD series, IMH of the ascending aorta carried an in-hospital mortality of 39%, a value not statistically different from the 30% in type A dissection. Mortality was a function of the presumed site of the origin for IMH; the more proximal the IMH, the greater mortality observed21.

Studies from Japanese and Korean groups showed that medically treated patients with IMH have low mortality, regardless of whether they are type A or g10,16-18,20. In Korean patients with type A IMH treated medically, only 1 out of 18 died, but 4 patients required pericardiocentesis or surgery for proximal dissection35. There are some reasons to justify these discrepancies: most Western studies are multicenter, and in them IMH comprises less than 10% of AAS21,32. Therefore, it is possible that most cases included represent the most complicated spectrum. On the other hand, most Asian reports are based on serial observations from a single center experience, and the relative incidence of IMH in AAS is 30%16-18,20. Based on these reasons, it seems that rather than a geographical or racial difference, the discrepancies in the results might be explained by a different severity in the IMH spectrum assessed.

Some studies have shown IMH reabsorption to be related to smaller aortic diameter5,16,24,30. In 22 patients with type A IMH, Kaji et al.34 showed that the group in which IMH regressed had a significantly smaller aortic diameter than the group in which IMH progressed or evolved to dissection or aortic rupture (47 ± 3 vs. 55 ± 6 mm), which suggested an optimum cutoff value of 50 mm, identical to that obtained in our series12 (Figure 14.5). Ide et al.36 observed that evolution to classical dissection was seen only in IMH with aorta diameter >50 mm. However, 54% of cases with aortic diameters <50 mm eventually progressed to dissection or rupture, challenging the Asian experience that IMH in a normal-size aorta precludes complications.

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