RESULTS
Phase one: Reliability assessment
We analysed the measurements from 15 patients (Group 1), including 30 observations for inter-rater variability and another 30 for intra-rater variability (Figure 1). The measurements from all three anatomical locations showed good correlation, agreement, and concordance.
Inter-rater agreement
We found a strong linear correlation between the two observers for all three readings (Figure 2b), and SAD at the umbilicus showed the best inter-rater concordance (ρc = 0.96, 95% CI 0.94–0.98) (Table S2). Bland-Altman plots also show that umbilical SAD had the best agreement (Figure 2c).
Intra-rater agreement
The first and second measurements of the observers were nearly identical. There was a strong linear correlation for all three measurements (r > 0.98). Concordance and Bland-Altman plots revealed a high agreement for all sagittal abdominal diameters (ρc>0.98) (Table S3).
Given the superior reliability of umbilical SAD, we tested its diagnostic accuracy to predict surgical morbidity in group 2.
Phase two: Evaluation of diagnostic accuracy and subgroup analysis
Thirty-five patients (20.4%) were excluded because of missing data. A total of 136 patients was analysed (Figure 1).
We found that umbilical SAD (u-SAD) was normally distributed in our sample (mean 239 ± 40 mm SD) (Table 1). Patients who encountered surgical morbidity had a significantly higher u-SAD compared with those without surgical morbidity (mean 243 ± 39 mm vs. 230 ± 36 mm,p =0.03).
In the univariate analysis, only the waist-hip ratio (WHR) and u-SAD showed a significant association with the main outcome measure (p <0.05). Despite these findings, when we assessed their diagnostic accuracy as a single measurement, neither of them proved to be clinically useful to predict surgical morbidity (AUC<0.70).
We found that nearly half of intraoperative complications occurred during the para-aortic lymph node dissection (6/14). A higher measurement of u-SAD was significantly associated with an incomplete lymphadenectomy (p <0.001). We also found a strong positive correlation between the conversion rate and the u-SAD measurement, although this was not statistically significant (Figure S1). The rest of the surgical morbidity variables were not independently associated with the u-SAD measurement.
The vast majority of patients in group 2 (Table S4) underwent a hysterectomy, bilateral salpingo-oophorectomy, pelvic and para-aortic lymphadenectomy (85.3%); only eight patients underwent exclusively para-aortic lymphadenectomy. The most frequent histopathology was endometrioid (53.7%) followed by serous (21.3%) neoplasia. Previous surgery, either open or laparoscopic, was not associated with the primary end-point. The median follow-up was 31 months (IQR 15–52).
We observed 17 deaths, but only two of them were grade V operative complications (both within 30 days of the surgery). One of them was directly associated with the procedure (bowel perforation), and the other one was a patient who suffered a stroke 5 days after surgery. Thirteen patients died from disease progression and the remaining three from other metastatic malignancies (breast cancer and multiple endocrine neoplasia).
Subgroup analysis
All subgroups were uniformly distributed (Figure 1), even though patients were originally randomized only to the para-aortic lymphadenectomy technique.
Intraoperative complications were more frequent in the transperitoneal vs. extraperitoneal subgroup (9 vs. 5), but this difference was not statistically significant (p =0.173). We found a significant negative correlation between u-SAD and aortic lymph node yield in the transperitoneal group (p <0.001), but no correlation was observed in the extraperitoneal subgroup (p =0.115) (Figure S2).
In the transperitoneal subgroup, BMI and u-SAD showed a significant independent association with the primary end-point (p <0.05). In this same subgroup, u-SAD was significantly higher in patients who encountered surgical morbidity (Figure 3a). In contrast, in the extraperitoneal subgroup, the main outcome was independent of the u-SAD measurement (Figure 3b).
We compared the diagnostic accuracy of u-SAD with the other anthropometric measurements of obesity in the transperitoneal subgroup, and u-SAD outperformed the others (Figure 3c). The discriminatory power was good in the transperitoneal subgroup, but poor in the extraperitoneal one (Figure 3d). In the subgroup of patients who underwent transperitoneal para-aortic lymphadenectomy by conventional laparoscopy, the diagnostic accuracy was higher (n=34, AUC=0.78).
In patients who underwent staging by the extraperitoneal technique, surgical morbidity was more frequently observed in those operated by conventional vs. robotic-assisted laparoscopy (52.6% vs. 28%,p =0.05) (Table S4).
Optimal cut-off point estimation
For patients undergoing para-aortic lymphadenectomy by the transperitoneal technique, we determined that 246 mm was the optimal cut-off point for u-SAD as a predictor of surgical morbidity. Using this value, the sensitivity and specificity were 0.56 and 0.80 respectively (NPV 0.69, PPV 0.70).