A patient presents with acute renal failure (ARF) and complete anuria. The USG is normal. Which of the following investigation will give best information regarding renal function.
D i.e. DTPA scan Antegrade pyelography (AP) & retrograde pyelography (RP) are invasive techniques. Percutaneous AP done by puncturing the collecting system & injecting contrast is rarely performed for diagnostic imaging purpose as ultrasound or CT may be used to visualize the ureter even in presence of abnormal renal function. However the indications of AP may be percutaneous nephrostomy (Whitaker test), to obtain renal urine for cyto/bactero-logical examination, to pinpoint obstruction level in dialated urinary system not adequately opacified by IVU/or after failed RP. Retrograde ureteropyelography (RP) is valuable when (IVU/IVP) is suboptimal owing to poor renal function & in cases where IV contrast administration is contraindicated. Intravenous urography/pyelography (IVU/IVP) is intravenous administration of iodinated contrast and taking renal x-rays. It is initial technique in evaluation of possible urinary obstruction. For taking additional radiographs rule of 8 (i.e. if no contrast appears in collecting system by 15 min after injection, there is a little reason to obtain next film until 2 hours (=15x8) later) prevent multiple exposure. There has been a significant decline in use of IVU as dominant imaging technique in obstruction d/ t fear of contrast induced nephrotoxicity and d/ t growth of renal sonography & low dose CT. The main draw back of IVU is that it is time consuming. Conventional gray scale sonography is good screening method for detecting subacute and chronic obstruction as demonstrated by pyelocaliectasis however, in acute obstruction pyelocaliectasis is minimal or absent. Another drawback is its inability to realibly distinguish mild hydronephrosis from normal or prominent extrarenal pelvis. Duplex & color Doppler ultrasound have yielded advances in: - distinguishing mild pyelectasis from prominent central renal blood vessels. - detecting high grade acute ureteric obstruction through analysis of ureteral jets (normal ureteral jets i.e. ejection of urine from ureter into urinary bladder are bilaterally symmetrical). - estabilishing renal resistive index (RI) as an independent hemodynamic measure of urinary obstruction. CT scan has emerged as an effective imaging tool in evaluation of acute renal obstruction esp in screening patients with acute flank pain / azotemia who are strongly suspected as having obstruction and in establishing the etiology of ureteral obstruction when other investigations have failed. Non contrast low dose CT is very quick & useful in determining the presence or absence of obstruction and have higher sensitivity for detection of ureteric stones as compared to IVU. The radionale for CT urography is that high risk patients or patients with hematuria can be fully investigated by a single imaging technique with a high degree of sensitivity & specificity. The major disadvantage is the radiation dose of CTU which is upto 5 times higher than IVU. Radionuclide renography has limited role in evaluation of acute obstruction as it lacks precise anatomical delineation of obstruction as well as ability to define the cause of obstruction. Its major use is in differentiation of a dilated non obstructed system from a paially obstructed system. When IVU demonstrates a dilated collecting system and there is doubt about the presence or absence of obstruction diuresis (frusemide) renography with Tc99 DTPA or MAG-3 will usually help to distinguish obstructive from non-obstructive dilatation & will localize the site of obstruction. The collecting system activity washes out with in 10minutes in non obstructive after diuresis challenge but no or paial response is seen in obstructive cases. Measurement of differential renal function can be made during diuresis renography or as a separate procedure using Tc99 DMSA examinationQ. MR urography is an ideal technique in pregnancy, where there is contrast allergy, renal failure patients & if radiation dose is an issue. The level of obstruction is always identified however ureteric abnormalities (if < 4mm) are poorly defined & that includes stones.
Intravenous Pyelogram
Retrograde Pyelography
Antegrade Pyelography
DTPA scan (Radiorenogram)