The impact of hydration on renal measurements and on cortical echogenicity in children

Kidney ultrasonography is frequently performed in children; to date there are no specific guidelines regarding hydration before the examination. Because certain renal measurements can be indicative of pathology, we used sequential US images to investigate the effect of standardised hydration in children relative to renal size, echogenicity and pelvic expansion. Thirty-one children (7 years to 14 years old) underwent US examinations before hydration (T0) and at 30 min (T30) and 60 min (T60) after ingesting water. We measured bladder volume, inter-polar kidney size, renal volume and anterior-posterior diameter of the pelvis. Cortical echogenicity was compared to that of the liver and spleen. On the right side the increase in average inter-polar renal size was 2.5% at T30 and 2.6% at T60 (P < 0.05) compared to T0. On the left the increase was 3.8% at T30 and 4.3% at T60 (P < 0.05). Volume expansion for the right kidney was 16.8% at T30 and 14.0% at T60 (P < 0.05). On the left it was 12.9% at T30 and 10.2% at T60 (P < 0.05). Cortical echogenicity progressed from hypoechogenicity to isoechogenicity (P < 0.05). The percentage of expanded pelves increased with hydration (T0: 3.2%, T30: 9.7%, T60: 22.6%). Oral hydration influences renal length, volume and echogenicity in children. Hydration results in expansion of the pelvis. We recommend standardisation of hydration before US examination.