Melamine-induced urinary calculi in infants—sonographic manifestations and outcomes 1 year after exposure

Abstract

In 2008, the melamine-tainted-milk incident started with reports of increased incidence of urolithiasis in infants in China. Affected children were screened for urolithiasis. The purpose of this study was to analyze sonographic characterization of infant melamine-induced urolithiasis. Transabdominal US examination was done in 603 infants with melamine-induced calculi. The imaging characteristics of calculi and hydronephrosis were analyzed. Follow-up US imaging was performed. Comet-tail sign was seen behind the calculus of <4 mm. Calculi of ≥ 4 mm were found in 299 inpatients with clear posterior border and with or without light shadowing. Solitary and multiple stones had similar incidence. Incidence of calculi in the inferior renal calyx was the highest (55.2%) in inpatients. Calculus size in inpatients age 2-3 years was smaller than that of children younger than 2 years old (P < 0.05). Inpatients age 2-3 years had the highest incidence rate (48.0%) of hydronephrosis. Calculi of <4 mm manifested as hyperechoic foci near the renal papillae, while calculi of ≥ 4 mm usually manifested as echogenic foci with visible inferior edge in the renal calyx. Hydronephrosis was a common imaging finding in inpatients ages 2-3 years.