Reply to “Crista aortae ascendentis, ascending aortic fold or Rindfleisch's fold—an enigma”

We are indebted to Mr. John for highlighting some important articles describing the anatomy and function of the crista aortae ascendentis, the aortic fold or ridge, and have studied them carefully. We concur that probably the first published report of this structure was by von Rindfleisch in 1884 and that it has been described subsequently by others. We note that the most recent account was the gross analysis by Lebona (1993) and, in this letter, are adopting the term aortic fold in deference to his study. Our histological identification of nerves within the fold is, we believe, an original finding (Morrison et al., 2003). We share Mr. John’s interest in the significance of the aortic fold. He refers to the studies by Gross (1921) and Robertson (1930). Gross (1921) made detailed radiological studies of age changes in the coronary circulation and reported the development of “fatvessels” or “arteriae telae adiposae” from the second decade onwards. These vessels are particularly well represented by the seventh decade and in specimens with atherosclerosis. Gross suggested that they represent a developing compensatory system between the right and left coronary arteries. Gross, however, described these fat-vessels as a general phenomenon, and although certainly present on the anterior surface of the ascending aorta, they were also reported throughout the fat of the epicardium. Robertson (1930) drew similar conclusions. The studies by Gross (1921) and Robertson (1930) almost certainly involved the aortic fold, yet did not examine it specifically. Although we accept the likelihood of the blood vessels of the aortic fold enlarging with age, we agree with our colleague that the concept of the fold forming to provide a collateral circulation can almost certainly be excluded on account of the size of the vessels involved, even in advanced coronary artery disease. The presence of the fold in fetal life and infants also weighs heavily against this view. Parke and Michels (1966) were able to study the development of the ridge that first became visible by the 16th week of gestation and reached its definitive shape and size relative to the aorta by the 8th month of fetal life. Their study is probably the first specific description of the aortic fold. A mechanical function seems more likely. It remains to be determined, however, whether the ridge develops through active or passive processes. Von Rindfleisch (1884) suggests that the fold appeared as a consequence of the perpetual expansion and contraction of the aorta. Because the elastic media under the ridge does not show any defect, however, it is unlikely that ridge develops from forces in the wall of the aorta. More realistically, Parke and Michels (1966) suggested that it provides protection from the friction of the movement of the right atrial appendage. We, in contrast, are more of the opinion that the ridge is the result of the movement of the right atrial appendage against the ascending aorta rather than being formed to aid its contact. The structure is visible in the neonate (Parke and Michels, 1966), however, as the heart starts beating between the 4th and 5th week of gestation (Impey, 1999), this is not surprising. We have made the following observations in our patients at surgery. In the presence of normal cardiac anatomy, the aortic fold is 2–3 cm long, 0.5 cm wide, and lies obliquely across the anterior aspect of the ascending aorta. The right atrial appendage is a blunt, triangular structure with one apex pointing superiorly, in contact with the ascending aorta. During systole, as the ventricles contract, the apex of the appendage moves briskly in an arc, along the length of the aortic fold from the anatomical right to left. As the ventricles relax during diastole and the atria fill, the tip of the appendage moves in the reverse direction back to its neutral position. The movement is not forceful, but elegant, as if the tip glides along the line of the fold. We suggest that this constant gentle rubbing of the ascending aorta leads to the accumulation of soft tis-