Purpose: This prospective study was designed to determine the effect of patient positioning on sonographic measurements of renal length in children. Materials and methods. Two dedicated pediatric ultrasonographers (observers A and B) measured the sonographic lengths of 48 kidneys in 25 children (two had unilateral renal agenesis). Each observer obtained the two "longest possible" measurements for each kidney with the patient in three positions: supine, contralateral decubitus, and prone. Patients with myelomeningocele, hydronephrosis, and renal cysts were excluded.
Results: Both examiners obtained significantly higher values for renal lengths with the children lying supine (observer A P </= 0.0017; observer B P </= 0.0409) or in contralateral decubitus (observer A P </= 0.0001; observer B P </= 0.0419) than with them lying prone. There was no significant difference between the supine and decubitus measurements. The mean difference between the supine and prone measurements for the observers was 3.0 mm for observer A and 1.8 mm for observer B. The mean difference between the contralateral decubitus and prone measurements was 3.0 mm for observer A and 1.6 mm for observer B.
Conclusion: Sonographic measurements of renal length made with the patient lying supine or in contralateral decubitus yield slightly higher values than those made with the patient prone.