Commonly 6 − 0 to 8 − 0 gauge are used for ureteral suture in felines [1–11], whose outside diameter is equivalent to that of New Zealand rabbits, corresponding to 1 mm [20]. The thickness of the 6 − 0, 8 − 0 and 10 − 0 sutures represents, respectively, 20 mµ, 40 mµ and 70 to 99 mµ [21], and although the three diameters are considered thin for general surgical procedures, it is noted that, for millimeter structures such as the ureter, this difference is an important characteristic regarding to the non-compromise of the lumen. Using thicker sutures, coupled with traumatic needles and with the inappropriate aid of magnification, makes ureterorrhaphy a challenging procedure [11], corroborating the high rates of complications described so far [4, 6, 7, 11].
Due to the widespread use of rabbits in experimental research, some studies [22–24] describe and compare the measurements and sonographic characteristics of healthy animals. They all point to a positive correlation between kidney measurements and animal weight, which can also be observed in this study, because, despite the measures of renal length and width of the control group, consisting of the non-operated contralateral kidney and ureter, being smaller than those described for white New Zealand rabbits [24], the animals used here had a lower average weight, justifying the difference found. In addition, another study [23], obtained similar renal measurements in 21 mixed breed animals, having an average weight equivalent to that reported in this study.
Changes in kidney size have been correlated with kidney disease and some specific pathological processes, such as hydronephrosis, are involved in increasing length and width [25]. In the first ultrasound assessment, all groups obtained differences with the control group, but not between them when comparing renal length. The width obtained more discreet increases, showing no difference with the control. Considering that acute changes result in larger kidneys, it is possible to correlate the increase in these measures with inflammation and ureteral edema resulting from the surgical procedure [11], causing luminal narrowing and urine accumulation in the kidney in different proportions. These results are reinforced by comparing the data obtained in the second ultrasound assessment, where the difference significant length and width were no longer with the control group but with the N6, due to the loss of experimental plots.
The remodeling and the repairing of the operated tissue is directly related to the diameter of the suture material [26], so, with the exception of the renal width at the 30th day, it is possible to observe that, in the two ultrasound evaluations, the renal measurements developed largest changes according to the greater caliber of the suture used. In relation to the renal pelvis, when there is no dilation, this structure is not normally seen on ultrasound and subtle dilations may also go unnoticed [23, 27]. The dilation indices obtained in this study corresponded to the ureteral dilation seen in the ultrasound exams, in which the N8 had the largest ureteral diameters in the first exam and all animals in this group presented the pelvis dilated. The other two groups showed decreasing changes for pelvic dilation and ureteral diameter, according to the thickness of the suture material used (4 animals in N6 and 3 in N10). At 30 days, these two parameters decreased in all groups, particularly in N6 due to the loss of experimental plots, reaffirming that the increase in measurements occurs mainly due to acute changes [11, 27].
The ureters follow the pattern of the renal pelvis and are only seen on ultrasound when they are dilated [3, 7, 27, 28] and the group operated with 8.0 suture was the only one that developed a significant increase in diameter in the first ultrasound assessment. The animals in this group also had high scores for ureteral inflammation, presence of stenosis and dilation at the suture site, in addition to macroscopic renal changes in greater numbers. Although widely used to perform ureterorrhaphy [1–11], 8 − 0 sutures are associated with high rates of postoperative complications, making them unsuitable for this procedure in ureters of rabbits, or other species with similar ureteral diameter. Although the 10 − 0 obtained slight increases in ureteral diameter in the first and second exams, these were not significant and reduced considerably between the two evaluations. These results suggest that the use of a thinner material in the ureteral suture is more appropriate [11].
The non-dilation of the ureters of group N6 is associated with urinary leakage into the abdominal cavity and consequent uroabdomen, since the majority of animals operated with this gauge of suture died between the two evaluations and a substantial amount of exudate on necropsy exams, associated with severe peritonitis was found. The uroabdomen is the most frequently described postoperative complication in association with ureterotomies [1, 3, 4, 7–10, 19, 29]. However, confirmatory tests comparing serum creatinine and that present in free abdominal fluid were not performed.
Although non-absorbable suture materials are not recommended for use in urinary tract surgeries due to the greater probability of acting as a starting point for the stones formation [17], a recent study [26] evaluated the behavior of 3 synthetic absorbable suture materials in urinary vesicles of rabbits in 2 phases and the formation of lithiasis was observed between the 3rd and 6th week in two of the groups evaluated. Thus, the formation of lithiasis seems to be associated with the contact of the suture with the urine, and the tissue response is directly related to the diameter used or to the presence of inflammation, infection, urinary pH and longevity of the material [17, 30]. In the present study, the group operated with 8 − 0 was the only one to present formation of lithiasis in the 4th week after surgery, a similar time to the study mentioned above, and it is likely that, because it has a thicker caliber, this suture has come into contact with the urothelium. The non-formation of stones in the N6 group may be associated with the early death of the animals. Microscopically, in the N6 group, areas of necrosis were observed, validating the blackened areas found in macroscopy. Even though this group presented the same amount of alterations in the 10 − 0 caliber renal form, this can be explained by the early death of the animals due to extravasation and peritonitis. This fact is also associated with the non-occurrence of fibrosis in this group, since this response results from prolonged inflammatory processes [7, 11].
Any ureteral surgical intervention can cause a disturbance in the healing remodeling phase, resulting in fibrosis, obstruction in various degrees and consequent hydronephrosis [12]. Therefore, despite presenting hydronephrosis and renal and ureteral inflammatory changes, according to the results presented, it is noted that these numbers are lower with the 10.0 suture and that these changes occur mainly acutely, in the immediate postoperative period, reducing with the progression of ureteral healing. The limitations of this study include not performing tests for serum creatinine and abdominal fluid to confirm urinary leakage in one of the groups, as previously discussed, and not performing a histopathological evaluation at 5 days postoperatively, to ascertain the changes caused acutely by sutures, this was not done in order to reduce the number of animals used, since it would be necessary to have a larger number of samples in each group for the histopathological evaluation in two stages.