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Radiological Test


Radiologic test

Vital points:


IVU define the site of obstruction.

In the presence of obstruction, the appearance time of the nephrogram is delayed. Eventually the renal image becomes more dense than normal because of slow tubular fluid flow rate, which results in greater concentration of contrast medium. The kidney involved by an acute obstructive process is usually slightly enlarged, and there is dilatation of the calyces, renal pelvis, and ureter above the obstruction. The ureter is not tortuous as in chronic obstruction.

In comparison with the nephrogram, the urogram may be faint, especially if the dilated renal pelvis is voluminous, causing dilution of the contrast medium. The radiographic study should be continued until the site of obstruction is determined or the contrast medium is excreted.

Retrograde or antegrade urography (RGP and AGP)

To facilitate visualization of a suspected lesion in a ureter or renal pelvis, retrograde or antegrade urography should be attempted. These diagnostic studies may be preferable to the intravenous urogram in the azotemic patient, in whom poor excretory function precludes adequate visualization of the collecting system. Furthermore, intravenous urography carries the risk of contrast-induced acute renal failure in patients with proteinuria, renal insufficiency, diabetes mellitus, or multiple myeloma, particularly if they are dehydrated. The retrograde approach involves catheterization of the involved ureter under cystoscopic control, while the antegrade technique necessitates placement of a catheter into the renal pelvis via a needle inserted percutaneously under ultrasonic or fluoroscopic guidance. While the antegrade approach may provide immediate decompression of a unilateral obstructing lesion, many urologists initially attempt the retrograde approach unless the catheterization is unsuccessful or general anesthesia is contraindicated.

Voiding cystourethrography (VCUG)

VCUG is of value in the diagnosis of vesicoureteral reflux and bladder neck and urethral obstructions. Patients with obstruction at or below the level of the bladder exhibit thickening, trabeculation, and diverticula of the bladder wall. Postvoiding films reveal residual urine. If these radiographic studies fail to provide adequate information for diagnosis, endoscopic visualization by the urologist often permits precise identification of lesions involving the urethra, prostate, bladder, and ureteral orifices.


is useful in the diagnosis of specific intraabdominal and retroperitoneal causes of obstruction. The unenhanced helical CT is the preferred study to image obstructing urinary calculi in the patient with colic, and it is also useful in imaging nonobstructing calculi in the patient with hematuria.

Radionuclide scan

though sensitive for the detection of obstruction, define less anatomic detail than intravenous urography and, like the urogram, are of limited value when renal function is poor. They have a role in patients at high risk for reaction to intravenous contrast. Patients suspected of having intermittent ureteropelvic obstruction should have radiologic evaluation while in pain, since a normal urogram is commonly seen during asymptomatic periods. Hydration often helps to provoke a symptomatic attack.


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