Visceral to total obesity ratio and severe hydronephrosis are independently associated with prolonged pneumoperitoneum operative time in patients undergoing laparoscopic radical nephroureterectomy for upper tract urothelial carcinoma

Patient population

A total of 169 patients diagnosed with UTUC at Keio University Hospital from January
2000 to December 2013 were treated by radical nephroureterectomy. Of these patients,
ORNU was performed in 91 and LRNU in 78. We excluded LRNU patients with a history
of muscle-invasive urothelial carcinoma of the urinary bladder (n = 5) and those who
were treated with neoadjuvant chemotherapy (n = 3). Thus, 70 LRNU patients were finally
included in our study population. No patient underwent endoscopic resection prior
to LRNU in our population. Basically LRNU was performed for clinical T3 or less UTUCs
without positive lymph node or distant metastasis (cTa-3N0M0). Of the 70 patients,
52 (74.3%) were men and 18 (25.7%) were women. The tumor was located in the renal
pelvis in 37 (52.9%) patients and the ureter in 33 (47.1%) patients.

This study was approved by the Institutional Review Board of Keio University School
of Medicine.

Surgical procedure

LRNU was performed according to the standard procedure, in other words, extrafascial
dissection of the kidney with 2/3 of the length of the ureter resected together under
laparoscopic procedure. Under general anesthesia, the patient was placed in the lateral
decubitus 60° flank position. LRNU was performed using either a transperitoneal approach
or retroperitoneal approach for extirpation of the kidney, and a small iliac incision
(Gibson incision) was made to retrieve the kidney and ureter en bloc and to perform
resection of the bladder cuff. The laparoscopic procedures were performed with 3 trocars,
and 1 trocar was added for liver retraction during right LRNU in the transperitoneal
approach. Routine regional lymph node dissection was not performed.

To accurately determine the technical difficulty associated with LRNU, we divided
the total procedure into three categories; extirpation of the kidney, bladder cuff
excision, and total operation. We then measured the operation time in each group and
defined total surgical operative time as the sum of the pneumoperitoneum time and
bladder cuff excision time. Pneumoperitoneum time was defined as the time from infusing
pressurized CO
₂
gas after port insertion to extirpation of the kidney by retrospectively reviewing
the videotapes in each case.

Assessment of obesity related parameters and hydronephrosis

Total fat area (TFA), visceral fat area (VFA), and subcutaneous fat area (SFA) were
measured at the level of the umbilicus using CT according to a procedure described
and validated previously (Kobayashi et al. 2002]; Seidell et al. 1987]). The tomographic attenuation of the adipose tissue was defined to be between ?50
and ?150 Hounsfield Units. As shown in Figure 1, the border of the intra-abdominal cavity was outlined on the CT image, and TFA and
VFA were then quantified using standard software (Advantage Work Station). The SFA
was calculated by subtracting VFA from TFA. In order to estimate the degree of proportional
adipose tissue distribution, we developed the VFA/TFA ratio calculated on the basis
of measured data, as a practical and standard parameter for the type of obesity using
CT scan. Two genitourinary radiologists completed all the measurements and were blinded
to the clinical details of the subjects. BMI was also calculated for all patients.

Figure 1. Graphics showing a method for determining the degree of fat distribution on computed
tomography. a Area inside the red line is total fat area (TFA). b Area inside the red line is visceral fat area (VFA).

For grading the degree of ipsilateral hydronephrosis, preoperative CT images and/or
MRI images were obtained by two genitourinary radiologists who were blinded to the
clinical details. Ipsilateral hydronephrosis was graded from 0 to 4 according to the
classification of Cho et al. (2007]). Cases without calyx or pelvic dilation were classified as grade 0, cases with pelvic
dilation only were classified as grade 1, cases with mild calyx dilation were classified
as grade 2, cases with severe calyx dilation were classified as grade 3, and cases
with calyx dilation accompanied by renal parenchyma atrophy were classified as grade
4 hydronephrosis (Ito et al. 2011]). Furthermore, we reviewed the degree of perinephric stranding, defined as linear
area of soft tissue attenuation in the perinephric space, for each kidney on CT. Stranding
was graded as 0 (no stranding), grade 1 (thin rimlike mild stranding), and grade 2
(diffuse, thick-banded severe stranding) as previously used and described in the literature
(Kim et al. 2013]; Davidiuk et al. 2014]).

Statistical analysis

All variables are expressed as the mean ± standard deviation. Associations between
clinical factors and the related operative parameters were analyzed using the Chi
square test and Mann–Whitney U test for categorical and continuous variables, respectively.
By considering the mean amount of the variables, we defined VFA/TFA ratio ?0.45 as
a dichotomous variable for visceral adipose accumulated group. Similarly, the mean
of each operating time (pneumoperitoneum, bladder cuff excision, and total operative
time) was used as a threshold value in order to discriminate between short and long
operative times. We chose mean operative time as a cut off value discriminating between
short and long operative times since previous studies adopted it as a clinically relevant
value (Hagiwara et al. 2011]; Hattori et al. 2014]). Univariate and multivariate logistic regression analyses were performed to identify
independent predictors for prolonged operative time. To identify the predictive factors
for surgical complexity during LRNU, we included age (?70 vs. 70), gender, BMI (?25 kg/m
²
vs. 25), clinical stage (stage 3 vs. 3), laterality, tumor location (renal pelvis
vs. ureter), tumor size (diameter ?20 mm vs. 20), surgical procedure (retroperitoneal
vs. transperitoneal), perinephric stranding (grade ?1 vs. grade 0), VFA/TFA (?0.45
vs. 0.45), and hydronephrosis grade (grade ?3, vs. grade 3). A 2-sided P value 0.05
was considered to be significant. All statistical analyses were performed using the
SPSS program, version 20.0. (SPSS Inc, Chicago, IL, USA)