Ultrasonographic features of nephrocalcinosis in preterm neonates

Nephrocalcinosis (NC) in preterm neonates has been reported frequently and small studies suggest an unfavourable effect on renal function. Data on ultrasonic features are limited and the reproducibility of ultrasonography (US) in detecting NC in preterm neonates is unknown. In this study, interobserver and intraobserver agreement of US was determined through videotape recordings of US examinations of preterm neonates. Furthermore, a prospective US study was performed in 215 preterm neonates (gestational age < 32 weeks) to evaluate ultrasonic characteristics, incidence, time course and effect on kidney length of NC. Patients were studied at 4 weeks after birth and at term. Patients with NC were followed for 2 years. NC was defined as bright reflections in the medulla or cortex seen in both transverse and longitudinal direction. The length of the kidneys was noted. The kappa value was 0.84 for intraobserver and 0.46 for interobserver agreement, whereas the overall agreement was 73%. NC was found in 50 of 150 (33%) patients at 4 weeks and in 83 of 201 patients (41%) at term. NC was localized mainly in the medulla. At 1 and 2 years, NC had persisted in 36% and 26%, respectively, of the patients with NC at term. Kidney length was comparable with normal values. In conclusion, US has a very good intraobserver agreement but a moderate interobserver agreement in detecting NC. Medullary NC is common among preterm neonates. During the first 2 years of life, the incidence decreases spontaneously and NC does not influence kidney length.