Nephrocalcinosis (NC) in preterm neonates has been reported frequently and
small studies suggest an unfavourable effect on renal function. Data on ult
rasonic features are limited and the reproducibility of ultrasonography (US
) in detecting NC in preterm neonates is unknown. In this study, interobser
ver and intraobserver agreement of US was determined through videotape reco
rdings of US examinations of preterm neonates. Furthermore, a prospective U
S study was performed in 215 preterm neonates (gestational age <32 weeks) t
o evaluate ultrasonic characteristics, incidence, time course and effect on
kidney length of NC. Patients were studied at 4 weeks after birth and at t
erm. Patients with NC were followed for 2 years. NC was defined as bright r
eflections in the medulla or cortex seen in both transverse and longitudina
l 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 medull
a. 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 in
terobserver agreement in detecting NC. Medullary NC is common among preterm
neonates. During the first 2 years of life, the incidence decreases sponta
neously and NC does not influence kidney length.