Perinephric fat thickness could aid in preoperative risk assessment in patients undergoing robot-assisted partial nephrectomy (RAPN), according to researchers.

In a study of 53 patients undergoing RAPN, a team at the University of Washington in Seattle led by Jonathan D. Harper, MD, found that increases in perinephric fat, especially medial and posterior fat, were associated with increased estimated blood loss (EBL) and operative time during the procedure. Each 1 mm increment in medial and posterior perinephric fat was associated with a 24 mL and 19 mL increase in EBL, respectively, and 3.3 minute and 3.3 minute increase in operative time, Dr. Harper’s group reported online ahead of print in the Journal of Endourology. Abdominal wall fat was not associated with either EBL or operative time.

“Perinephric fat measurements are independently associated with increased EBL and operative time in patients undergoing RAPN for small renal masses, and, if validated, prospectively, may have a role in development of enhanced clinical prediction tools,” the authors concluded.

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The researchers measured perinephric and abdominal wall fat based on magnetic resonance imaging and computed tomography scans nearest to the date of surgery.

Dr. Harper and his colleagues explained that obesity frequently is categorized by body mass index (BMI), but visceral and abdominal wall fat quantity vary with equivalent BMI. “Because perinephric fat around the kidney impacts the operative field, it is expected to be a superior predictor of complexity.”

Of the 53 patients in the study, 27 had a BMI below 30 kg/m2 and 26 had a BMI of 30 kg/m2 or higher (obese). The mean EBL differed significantly between the obese and non-obese patients (300 vs. 212 mL). Although obese patients had a 37 minute longer operative time on average, this difference did not reach statistical significance.

On multivariate analysis, however, increasing BMI was associated with increased operative time, but was not independently associated with EBL.

The obese patients had significantly greater perirenal fat (anterior, posterior, medial, and lateral) than the non-obese patients.