Objective To evaluate the application value of prone-position ultrasound in assessing retrorenal colon among patients scheduled for percutaneous nephrolithotomy (PCNL).

Methods A total of 651 patients scheduled for PCNL were enrolled. All patients underwent preoperative supine-position computed tomography (CT) and prone-position ultrasound to assess retrorenal colon. Retrorenal colon was defined as segment of the colon located posterior to the kidney, with its inferior margin extending beyond the lower pole of the kidney. The degree of coverage was classified as mild (≤3.0 cm), moderate (>3.0 cm without extending beyond the renal hilum) and severe (extending beyond the renal hilum). Patients diagnosed with retrorenal colon by ultrasound underwent further evaluation using prone-position CT. Concordance between ultrasound and supine-position or prone-position CT in diagnosing and classifying retrorenal colon was compared, and the impact on puncture pathway selection and surgical approach was analyzed.

Results Among 651 patients, prone-position ultrasound identified retrorenal colon in 57 patients, including 43 mild cases, 11 moderate cases, and 3 severe cases. Prone-position CT identified retrorenal colon in 55 patients, including 42 mild cases, 10 moderate cases, and 3 severe cases. Supine CT identified retrorenal colon in 26 patients, including 23 mild cases, 2 moderate cases, and 1 severe case. The detection rate of retrorenal colon by supine CT was significantly lower than that by prone-position ultrasound (P < 0.05). In 12 patients (4 mild cases, 7 moderate cases, 1 severe case), the puncture pathway was modified based on ultrasound diagnosis, and 2 patients with severe involvement underwent a change in surgical approach.

Conclusion Prone-position ultrasound demonstrates good agreement with prone-position CT in the assessment of retrorenal colon.