Ultrasound-Based Prediction of Skin-to-Renal Pelvis Distance for Percutaneous Renal Access.

BACKGROUND

Studies examining anatomical changes in the prone position during endourological procedures lack predictive formulas for estimating the renal pelvis-to-skin distance (KSD). Furthermore, existing equations for renal depth-an important parameter for accurate glomerular filtration rate (GFR) assessment-are based on supine measurements. This study aimed to develop predictive formulas for estimating renal depth in the prone position for patients undergoing percutaneous renal access.

METHODS

A total of 86 healthy volunteers (46 men, 40 women) were enrolled in a prospective study conducted at the 2nd Department of Urology, Papageorgiou General Hospital between June and September 2020. Participants completed a questionnaire on medical history, demographic, and somatometric characteristics. Renal KSD was measured ultrasonographically in the prone position using a convex probe placed parallel and 1 cm below the 12th rib, with the posterior axillary line as a landmark. The biopsy line targeted the midpoint of the renal pelvis. Distances were analyzed in relation to clinical and anthropometric variables, and predictive equations were generated for each kidney.

RESULTS

The following equations were derived: left kidney: distance = 1.5 + 0.272 × body mass index (BMI) - 0.452 × gender; right kidney: distance = 1.619 + 0.259 × BMI - 0.457 × gender (BMI: gender coded as 0 = male, 1 = female). Mean renal depth was 7.81 cm for the right kidney and 8.23 ± 1.47 cm for the left. Distances were significantly greater in men (p = 0.004 right; p = 0.005 left). A strong positive correlation was observed between right and left kidney depths (r = 0.859, p < 0.001), as well as with body weight and waist circumference. In men, greater right kidney depth was associated with hypertension, low high-density lipoprotein (HDL), and metabolic syndrome (p < 0.05).

CONCLUSIONS

These formulas provide a simple and reliable method for estimating renal depth in the prone position, potentially improving procedural accuracy and patient safety during percutaneous renal access.