# Volumetric Analysis of Aortic Changes after TEVAR Using Three-Dimensional Virtual Modeling
## 4 Discussion
They showed that an 11.6% increase in aneurysm volume between pre-operative and follow-up CTA was associated with the development of a type I endoleak, while a pre-operative thrombus volume of 11.3% of the total aneurysm was associated with a type II endoleak. They concluded that for predicting the presence of a high-pressure endoleak after TEVAR, volume change analysis performed better than diameter change analysis. Differently from [PERSON] et al., our study had a fixed range of CTA follow-up time after TEVAR (12 months instead of 6 months as a minimum), with a long clinical follow-up time (55.3 \(\pm\) 26.6 months). Compared to [PERSON] et al., our study specifically compared the diameters and volumes of the descending aorta between discharge and the 12-month follow-up after TEVAR, using the stent graft as a reference. In contrast, [PERSON]'s study compared the pre-operative volumes with those from the last available follow-up, which was at least six months post-TEVAR. Moreover, we analyzed both the diameters and volume changes in five different descending aortic segments, and not only at the level of the DTAA, for a more precise evaluation of the complex phenomenon of aortic remodeling after TEVAR, which may impact not only the aneurysmal sac but also other portions of the descending aorta, such as the stent graft landing zones and aortic necks. Nevertheless, we similarly observed that in patients who developed TEVAR-related complications, there was a net increase in the volume of the descending aorta, aneurysm, distal landing zone, and both the proximal and distal necks, and a relative increase (10%) in the global descending thoracic aorta volume at 12 months after CTA compared to the substantial stability of the same volume in the no-complication group. As far as segmental analysis is concerned, it is interesting to note that the greatest relative changes in volume were identified at the level of the distal landing zone and aortic neck, suggesting that these segments may be the most susceptible to pathologic remodeling and dilatation after TEVAR. This confirms what has already been expressed in the literature regarding the importance of the optimal selection of the distal landing zone for TEVAR [31; 32]. When comparing the results of both the diameter and volume changes, the diameter evaluations showed significant changes only at the distal landing zone of the stent graft, while volume analysis seemed to be more appropriate for identifying even small volume changes that occurred after TEVAR in all segments of the descending aorta, which may have been underestimated by the manual diameter measurements. Except for the identification of endoleaks or stent graft migration, the CTA follow-up using diameters in patients with TEVAR was based on the same principles of follow-up of native DTAA, with an aneurysm growth threshold of \(>\)5 mm/year identified as a feature of high-risk for a rupture aneurysm [33]. Still, there is no consensus on when to treat patients with re-TEVAR, as it is usually a multidisciplinary decision. Our results show a particularly high AUC score (0.906) for the net volume changes of the descending thoracic aorta (Figure 5, Table 4). Meanwhile, considering the volumetric variables for every single portion of the aorta (1, 2, 3, 4, 5), lower AUC scores were obtained. This indicates that a volume measurement considered as a whole (i.e., the entire descending thoracic aorta volume change) is more predictive than the volumetric changes in the single portions. In general, the AUC and the sensitivity/specificity scores were higher for volumetric parameters (especially for the net volume changes) than for the standard diameter evaluations, as shown in Table 4. In our study, 40 mL increases in the global descending thoracic aorta volumes after 12 months seemed to be predictive of TEVAR-related complications with high specificity (94%) and good sensibility (75%).