Figure 843

Diagnosis of obstructive nephropathy. A, Diuresis renography. B, Doppler ultrasonography. C, D, Magnetic resonance urogram utilizing a single shot fast spin echo technique with anterior-posterior projection (C) and left posterior oblique projection (D). Images demonstrate a widely patent right ureteropelvic junction in a patient with abdominal pain and suspected ureteropelvic junction obstruction. Administration of gadolinium is not required for this technique. Note also the urine in the bladder, cerebrospinal fluid in the spinal canal, and fluid in the small bowel.

Ultrasonography is the procedure of choice to determine the presence or absence of a dilated renal pelvis or calices and to assess the degree of associated parenchymal atrophy.

Nevertheless, obstruction rarely can occur without hydronephrosis, when the ureter and renal pelvis are encased in a fibrotic process and unable to expand. In contrast, mild dilation of the collecting system of no functional significance is not unusual. Even obvious hydronephrosis in some cases may not be associated with functional obstruction [70]. Diuresis renography is helpful when the functional significance of the dilation of the collecting system is in question [71,72]. Renal Doppler ultrasonogra-phy before and after administration of normal saline and furosemide also has been used to differentiate obstructive from nonobstructive pyelocaliectasis [73]. Other techniques such as excretory urography, computed tomography, and retrograde or antegrade ureteropyelography are helpful to determine the cause of the urinary tract obstruction. The utility of excretory urog-raphy is limited in patients with advanced renal insufficiency. In these cases magnetic resonance urography can provide coronal imaging of the renal collecting systems and ureters similar to that of conventional urography without the use of iodinated contrast. RI— resistive index. (C, D, Courtesy of B. F. King, MD.)

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