Renal measurements, including length, parenchymal thickness, and medullary pyramid thickness, in healthy children: what are the normative ultrasound values?

OBJECTIVE: The objective of our study was to develop, by use of ultrasound, nomograms of renal parenchymal thickness, medullary pyramid thickness (height), renal length, and the ratio of medullary pyramid thickness to parenchymal thickness in healthy children. SUBJECTS AND METHODS: This prospective study included 292 consecutive children (136 boys and 156 girls) who were referred between October 2008 and March 2009 for problems other than urinary tract symptoms or underlying kidney disorders. The children were between 1 month and 18 years old (mean age, 6.1 +/- 5.9 years). Real-time gray-scale sonography was performed with a linear or curved array transducer. All examinations were performed by the same experienced radiologist (16 years of experience in pediatric sonography at the time the study began). All the children were well hydrated and had full bladders at the time of examination. Renal length measurements were performed in the sagittal view, and the maximum length of each kidney was measured. Measurements of parenchymal thickness and medullary pyramid thickness were performed on the same image on which length measurements were made. Parenchymal thickness and medullary pyramid thickness were measured at the middle third portion of the kidney. The Wilcoxon's signed rank test was used for statistical analysis.
RESULTS: Nomograms of renal parenchymal thickness, medullary pyramid thickness, renal length, and the ratio of medullary pyramid thickness to parenchymal thickness were developed. When all age groups were pooled together, statistically significant differences were observed between right and left kidneys in terms of parenchymal thickness (p < 0.001), medullary pyramid thickness (p < 0.001), and renal length (left kidneys were longer, with thicker medullary pyramids and parenchyma; p < 0.001). A slight but significant difference in the ratio of medullary pyramid thickness to parenchymal thickness was observed (p = 0.045).
CONCLUSION: By use of renal sonography, nomograms of renal parenchymal thickness, medullary pyramid thickness, renal length, and the ratio of medullary pyramid thickness to parenchymal thickness were established in healthy children.