Masayuki Nakagawa, Department of Urology, Kagoshima University, Faculty of Medicine, 8-35-1 Sakuragaoka, Kagoshima 890-8520, Japan. Email: email@example.com
Abstract We report on a rare case of urinary silica calculi in a 10-month-old boy. The boy showed acute pyelonephritis with left hydronephrosis. Ultrasonography and computed tomography revealed a calculus at the left ureteropelvic junction and three additional calculi in the left renal pelvis. Because his acute pyelonephritis was refractory to conventional chemotherapy, the patient underwent successful left percutaneous nephrostomy followed by percutaneous nephrolithotripsy for the renal calculi. All stones disappeared and his postoperative course was uneventful. On infrared spectrophotometry, the wavelength pattern of the stones exhibited two peaks at 1100 and 1650 cm−1, consistent with the determination that the calculi consisted of a mixture of silicate (78%) and calcium oxalate (22%). We consider that the etiology of the calculi in this child can be ascribed to the silicate-rich water used to dilute milk. In Japan, 46 adult patients with urinary silicate calculi have been reported in the literature; however, there is no report of the disease in an infant in Japan.
Urinary calculi are rare in humans, with an incidence of 0.2% of all urinary calculi.1 There is a relationship between silicate ingestion and silicate stone formation. There are several reports1–3 showing that the long-term administration of magnesium trisilicate induces silica urinary calculi in adult patients with gastric and duodenal ulcers. However, renal silica calculi in an infant is extremely rare. To our knowledge, this is the first case report of renal silica calculi in an infant in Japan. We report this unusual case and discuss the etiology of the disease.
A 10-month-old boy was referred to our hospital for the evaluation and treatment of acute pyelonephritis with left hydronephrosis. He had been receiving some antibiotics, including cefotaxim and imipenem; however, his condition had not improved. On admission, the boy's height was 75 cm, bodyweight was 10 kg and body temperature 37.6°C. He was growing and developing normally. Physical examination was unremarkable except for the child being slightly irritable and grouchy. Peripheral blood count was as follows: white blood cells (WBC) 18 100 /µL, red blood cells (RBC) 397 × 104 /µL, hemoglobin (Hb) 9.6 g/dL, hematocrit (Ht) 30.2% and platelet count 58.1 × 104 /µL. Blood chemistry was unremarkable. Urinalysis revealed a pH of 7.5 and 70–80 WBC and 40–50 RBC per high-power field. Mild proteinuria was also observed in the urine. Urine culture revealed urinary tract infection with Escherichia coli (105 /mL). Ultrasonography revealed a calculus at the left ureteropelvic junction and three additional calculi in the left renal pelvis. An excretory pyelogram and plain computed tomography (CT) confirmed these findings (Fig. 1).
Because the boy's acute pyelonephritis was refractory to conventional chemotherapy, he underwent successful left percutaneous nephrostomy followed by percutaneous nephrolithotripsy for the renal calculi. All stones disappeared and his postoperative course was uneventful.
On infrared spectrophotometry, the wavelength pattern of the stones exhibited two peaks at 1100 and 1650 cm−1, consistent with the determination that the calculi consisted of a mixture of silicate (78%) and calcium oxalate (22%; Fig. 2). We found no metabolic abnormalities in the urine, such as hypercalciuria, hyperuricosuria, hypocitraturia and cystinuria.
The infant had been fed for 8 months on milk powder dissolved in water from a silicate-rich mineral water. The concentration of representative constituents of the mineral water is as follows: Na+ 61 mg/L, K+ 20.2 mg/L, Ca2+ 20.4 mg/L, Fe2+ <0.05 mg/L, Cl– 11.0 mg/L, HCO3– 238 mg/L, silica 172 mg/L, arsenate <0.005 mg/L and cadmium <0.005 mg/L.
Urinary silicate calculi are rare, with an incidence of 0.2% of all urinary calculi in humans.1 In Japan, 46 patients with urinary silicate calculi have been reported in the literature.4–7 However, all patients reported were adults aged between 24 and 77 years. It appears that our report is the first of urinary silicate calculi in an infant in Japan. As shown in the literature, urinary silicate calculi tend to occur in patients taking large amounts of antacids containing silicate, such as magnesium trisilicate.1,2 When a silicate reacts with acid in the alimentary tube, especially in the stomach, part of the silica is precipitated as a gel and part remains as a solution in the form of a colloid. The breakdown products, including various silicic acids, such as orthosilicic acid (H4SiO2), metasilicic acid (H2SiO3), trisilicic acid (H4Si3O8) and disilicic acid (H2Si2O5), can be readily absorbed across the intestinal wall and excreted rapidly in the urine. Alkalization by the gut fluid changes a silica colloid into a more soluble and absorbable compound.2,3 Urinary excretion rises markedly in proportion to the increase in silicate intake.
In the present patient, investigation of the etiology of silicate calculi found that the infant had been fed for 8 months on milk powder dissolved in water from a silicate-rich mineral spring. There is a relationship between silicate ingestion and silicate stone formation. A previous report has demonstrated that the urinary excretion of silicate is normally less than 10 mg/day but approaches 500 mg/day in adult patients taking magnesium trisilicate.8 It is difficult to determine the exact amount of silicate intake or silicate-rich water in our patient. However, we estimated that the amount of silicate-rich water intake was approximately 1000–1200 mL/day between 2 and 6 months of age. Therefore, the estimated silicate intake was approximately 172–206 mg/day, because the concentration of silicate in the spring water was 172 mg/L. We failed to the measure urinary concentration of silicate in our infant; however, the concentration of silicate in the spring water is between seven- and 34-fold higher than the average silicate concentration (5–25 mg/L) in tap water in other Japanese prefectures. No other foods containing silicate had been given to the infant. Taken together with these findings, we consider that the etiology of the calculi in the infant is ascribable to the silicate-rich water used to dilute his milk.
In terms of the treatment of silicate stones, in most cases the stones had been discharged spontaneously, although some recent cases have been treated by extracorporeal shock wave lithotripsy monotherapy. Our patient was treated by percutaneous nephrolithotripsy following percutaneous nephrostomy because he had been suffering from acute pyelonephroritis with hydronephrosis. We consider that the treatment for the disease should be chosen on the basis of the patient's condition.