Renal parenchymal injury after standard and mini percutaneous nephrostolithotomy

Purpose: Mini percutaneous nephrostolithotomy was developed for use in chil dren and in adults with a reduced renal reserve to minimize the morbidity a nd renal parenchymal damage presumed to occur with traditional percutaneous nephrostolithotomy. We compared the extent of renal injury incurred by dif ferent sized nephrostomy tracts in female farm pigs undergoing 11 or 30Fr p ercutaneous nephrostomy. Materials and Methods: Bilateral percutaneous nephrostomy was attempted via a mid or lower pole calix under fluoroscopic guidance in 6 pigs. In 2 pigs the procedure was unsuccessful on 1 side, leaving 5 successfully establish ed nephrostomy tracts on each side. In each pig the right percutaneous trac t was dilated with a 28Fr dilating balloon and a 30Fr Amplatz working sheat h (Cook Urological, Spencer, Indiana) was positioned in the collecting syst em. On the left side an 11Fr sheath (Cook Urological) was placed. The sheat hs were removed after 1 hour and nephrostomy tubes (22Fr on the right and 8 Fr on the left side) were left in place overnight and then removed. Six wee ks later the pigs were sacrificed and the kidneys were harvested. The nephr ostomy tracts were identified grossly and examined microscopically, and the fibrotic scar was measured using digital analysis. The volume of scar was estimated using the calculated volume of a cylinder. Results: At kidney harvest all 10 kidneys appeared grossly normal. No intra -abdominal urine collection or perirenal hematoma was noted. Mean estimated scar volume of the 30 and 11Fr tracts was 0.29 and 0.40 cc, which translat es into a mean fractional loss of parenchyma of 0.63% and 0.91%, respective ly (p not significant). Conclusions: Renal parenchymal damage resulting from the creation of a neph rostomy tract is small compared to overall renal volume regardless of the s ize of the nephrostomy tract. Consequently there is no advantage to the use of a small access sheath based on renal scarring alone.