Evaluation of painful hydronephrosis in pregnancy: Magnetic resonance urographic patterns in physiological dilatation versus calculous obstruction

Purpose: We evaluated magnetic resonance urography (MRU) appearances in symptomatic hydronephrosis in pregnancy and compared urographic patterns in physiological and calculous disease. Materials and Methods: A total of 24 consecutive pregnant women with symptomatic hydronephrosis underwent MRU, comprising an overview fast T2-weighted examination of the abdomen and pelvis, and thick slab, heavily T2-weighted MRU images, followed by focused, high resolution T2-weighted sequences obtained in an axial and coronal oblique plane through the level of ureteral caliber change. Results: Of these 24 pregnant women 15 were found to have physiological hydronephrosis, 7 had calculous disease and 2 had preexisting urinary anomalies. MRU findings in physiological hydronephrosis cases were extrinsic compression of the middle third of the ureter, no filling defect and a collapsed ureter below it. Obstruction by ureteral calculi was seen at points of ureteral narrowing in the ureter, that is at the vesicoureteral junction in 2 cases, in the compressed mid ureter in 3 and at the pelviureteral junction in 1. Nonobstructive renal calculi were seen in another patient. Calculi presented throughout pregnancy but physiological hydronephrosis presented only in the late second and third trimesters. With distal calculi the MRU appearance was the double kink sign with constriction at the pelvic brim and the vesicoureteral junction with a standing column of urine in the pelvic ureter. There was renal edema and perirenal extravasation. Small calculi were only identified using high resolution T2-weighted magnetic resonance imaging. Conclusions: MRU is a valuable and well tolerated investigation for evaluating painful hydronephrosis in pregnancy. There are characteristic and differing urographic appearances in physiological and calculous obstruction.