Strengths and Limitations
The main strength of our study is that it is the first one to assess the usefulness of SAD as a predictive tool for surgical morbidity. Few studies examine the role of a minimally invasive approach and the aortic lymphadenectomy technique in surgical morbidity, our study sheds light in this regard.
We believe u-SAD could have clinical applicability because of two reasons: preoperative imaging use is widespread, and u-SAD is reliable, straightforward, and easy to measure.
Also, this measurement is not limited to MRI, it has been described in CT-scans 33.
Research results in surgery are subject to several biases: surgeon volume, experience, and procedure complexity. In our study, these biases were mitigated because the surgeries were carried out in three referral hospitals, by a small group of expert oncologic surgeons; and most patients had the same diagnosis and underwent the same procedure. Since data were collected prospectively, this prevented observer and recall bias. The long-term follow-up helped to reduce underreporting, and the precise measuring of variables (e.g. haematocrit drop instead of estimated blood loss) reduced measurement error or estimator bias.
The major limitation of our study is the lack of validation of the core outcome set. Some variables were defined as percentiles (Table S1), so they are affected by the surgical results of each centre. This requires everyone to determine their cut-off point.
We did not include lymph node count in the composite outcome measure (but it was recorded and analysed), as we found in a previous study that all minimally invasive techniques yielded the same number of aortic nodes 24. Instead, we estimated surgical difficulty by accounting for the completion of the aortic lymphadenectomy.
We did not calculate the sample size for the second phase, and given the limited number of patients, some differences were not statistically significant.