Technologic advances in radiographic imaging have radically changed the diagnostic approach to upper urinary obstruction (Smith et al. 1999; Kawashima et al. 2004). For years, the radiographic gold standard in the diagnosis of acute urinary obstruction was plain radiographs (KUB) with or without tomography and excretory urography (EXU) (Hattery et al. 1988; Heidenreich et al. 2002). The KUB would provide important evidence on the presence of radiopaque stone disease. EXU provided both functional and anatomic detail regarding upper tract obstruction. Classic findings of upper urinary obstruction on EXU include a delayed nephrogram, persistent nephrogram, delayed excretion of contrast into the collecting system, and/or failure of contrast to enter the bladder on delayed films. In the setting of upper urinary tract obstruction, other associated findings can include contrast extravasation secondary to forniceal rupture or rarely pyelovenous/ pyelolymphatic backflow (Hattery et al. 1988). EXU can provide excellent detail of the calices, renal pelvis, and ureter, but anatomic detail of the renal parenchyma and surrounding soft tissues is poor in comparison to cross-sectional imaging techniques (Kawashima et al. 2004). EXU is also more time-consuming and labor-intensive than other imaging modalities. In addition, no-nurologic causes of urinary obstruction and flank pain are less optimally evaluated with EXU (Rucker et al. 2004). Performing EXU on patients with renal colic can also be problematic in the setting of ureteral obstruction. In the setting of ureteral obstruction, the osmotic effect of the contrast may result in a forced diuresis and subsequent fornix rupture and resultant urinoma. In the current era, emphasis has been placed on more advanced imaging techniques including ultrasonography (US), magnetic resonance imaging (MRI), and particularly computerized tomography (CT).
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