Significant unfavorable geometrical changes in ascending aorta despite stable diameter at follow-up

The clinical importance of following up on the ascending aortic diameter lies in the fundamental presumption that wall pathology eventually manifests as a change in shape. However, the diameter describes the vessel locally, and the 55 mm criterion fails to prevent most dissections. We hypothesized that geometric changes across the ascending aorta are not necessarily imprinted on its diameter; i.e. the maximum diameter correlates weakly and insignificantly with elongation, surface stretching, engorgement, and tortuosity.

Two databases were interrogated for patients who had undergone at least 2 ECG-gated CT scans. The absence of motion artifacts permitted the generation of exact copies of the ascending aorta which then underwent three-dimensional analysis producing objective and accurate measurements of the centreline length, surface, volume, and tortuosity. The correlations of these global variables with the diameter were explored.

Twenty-two patients, 13 male and 9 female, were included. The mean age at the first and last scan was 63.7 and 67.1 y, respectively. The mean diameter increase was approximately 1 mm/y. There were no dissections, while 7 patients underwent preemptive surgery. The yearly change rate of the global variables, normalized to height if applicable, showed statistically insignificant, weak, or negligible correlation with diameter increments at follow-up. Most characteristically, a patient's aorta maintained its diameter, while undergoing 1 mm/y elongation, 151 mm²/(y·m) stretching, 2366 mm³/(y·m) engorgement, and 0.02/y tortuosity.

Maximum diameter provides a local description of the ascending aorta and cannot fully portray the pathological process across this vessel. Following up the diameter is not suggestive of length, surface, volume, and tortuosity changes.