Ultrasonographic characteristics of urolithiasis in children exposed to melamine-tainted powdered formula.

BACKGROUND: Since the outbreak of renal diseases among children who had consumed melamine-tainted powdered formula in 2008, urinary system ultrasound examination was carried out for these children at our hospital. This study aimed to investigate the ultrasonographic characteristics of urolithiasis caused by melamine-tainted powdered formula.
METHODS: From September 12 to October 9, 2008, urinary system ultrasound examination for children after consumption of melamine-tainted powdered formula was carried out at the Children's Hospital of Zhejiang University, China. A total of 15,577 infants and children were subjected to the examination. A questionnaire with items including demographic characteristics, history of exposure and clinical symptoms were completed before examination.
RESULTS: Among the 15,577 children, 7988 were boys and 7,589 girls with age ranging from 1 month to 15 years (mean age, 22 months). Urolithiasis was found in 562 patients with an identification rate of 3.6%. Urolithiasis was identified mainly in the children aged 36 months or younger (88.6%). Unilateral kidney calculi were found in 431 children and bilateral kidney calculi in 131 children. Eleven of these children also had ureteric calculi, 1 had bladder calculi, 2 had urethral calculi, and 2 had gallbladder calculi. Fifteen children had urinary tract obstruction. Ultrasonographic characteristics of these melamine calculi were different from the calcium oxalate calculi, i.e., the lesions were less echogenic, had a more "sandy" appearance and were less dense. The posterior portion of the calculi could be observed and was accompanied with a feeble or absent acoustic shadow.
CONCLUSIONS: Melamine-induced calculi were ultrasonographically less echogenic, sand-like and discrete; the posterior portion of the calculi was accompanied with a feeble or absent acoustic shadow. It might be a new type of urolithiasis in children.