Functional aspects of silent ureteral stones investigated with MAG-3 renal scintigraphy

BACKGROUND: To investigate functional aspects of silent ureteral stones with special focus on obstruction and its relationship to renal anatomy. The present study is the first investigation of renal excretory function in patients with silent ureteral stones. METHODS: Patients with primarily asymptomatic ureteral stones underwent a mercapto-acetyltriglycine (MAG-3) renal scintigraphy prior to treatment, in addition to anatomic evaluation of renal units and serum creatinine levels. The primary outcome measure was the presence or absence of obstruction. Secondary outcome measures were kidney anatomy, grade of hydronephrosis, location of stones, stone size, and serum creatinine levels. RESULTS: During a ten-year period, 14 patients (median age 52.6 years; range 37.3 to 80.7 years) were included in the study. The relative frequency of primarily asymptomatic ureteral stones among all patients treated for ureteral stones in the study period was 0.7%. Eleven renal units showed some degree of hydronephrosis while 3 kidneys were not dilated. On the MAG-3 scan, 7 patients had an obstruction of the ureter, 5 had no obstruction, and 2 had dysfunction of the kidney. A statistically significant correlation was established between the grade of obstruction and stone size (p = 0.02). CONCLUSIONS: At the time of presentation, only 64.3% of the patients revealed an obstruction in the stone-bearing renal unit. The degree of hydronephrosis and renal function were very diverse in this subgroup of patients with ureteral stones. The onset of ureterolithiasis and the chronological sequence of obstruction remain unclear in patients who have never experienced symptoms due to their stones.