Joint Program in Nuclear Medicine

Diuresis Renogram

Chandra Dass, MD 
Finn Mannting, MD PhD

November 26, 1996

Presentation

A 28 year old female with a six year history of left flank pain occuring mostly while lying down, was discovered by pelvic ultrasound to have left hydronephrosis. An intravenous urogram revealed normal right kidney and the left kidney revealed mild to moderate dilatation of the intrarenal collecting system upto the level of the UPJ, that was most likely congenital. Blood chemistry was within normal limits.

Imaging Findings

A MAG-3 Lasix Renogram was performed and showed prompt excretion of activity from the right kidney, but an obstructed pattern on the left side (shown on time-activity curves from a region-of-interest over the collecting system). There was symetric renal function.

Follow Up

The patient underwent a left pyeloplasty, and has been asymptomatic since.

Discussion

Urinary tract obstruction is a very common problem that, if untreated, may lead to progressive renal damage. Acute obstruction is diagnosed clinically and by radiological techniques. Uptake of radioactive tracer varies from no uptake at all to normal uptake depending on the pressure build-up in the obstructed collecting system and time. Radionuclide function measurements have limited prognostic value in acute obstruction. Chronic obstruction leads to the compromise of renal function. Radiologic techniques (excretory and retrograde urogram), CT and US accurately define the anatomy of the involved portion of the urological tract and the pathology of the lesion but not the functional status of the individual kidneys in a simple quantitative manner. The flow, uptake, and excretion of tracers accurately reflect the functional status of each kidney and are used to follow the renal function after therapeutic interventions. Invasive testing often may be necessary to predict the functional recovery (1).

From the use of antegrade perfusion pressure flow test (Whitaker test), it became clear that dilated systems are not always obstructed, and this differentiation is clinically relevent in the further patient management. Whitaker test, though not dependent on renal function, is invasive and provides no information about the functional status of the kidneys. Diuretic renogram is noninvasive, provides functional information, but very poor renal function may invalidate the study since test results depend on tracer uptake followed by diuresis induced washout (2). Tubular agents are preferred and currently Tc99m MAG - 3 is widely used for its high extraction fraction, rapid parenchymal transit, low radiation absorbed dose and excellent imaging properties. The standard acquisition parameters used are LFOV camera with LEAP collimator, 128 x 128 matrix in 10-30 sec / frames, displayed as 2-5 min images. Time activity curves are generated (Renogram Phase: Whole kidney ROI and 2 pixel thick ring around kidney for background; Diuretic Phase: Renal pelvis ROI and infero-lateral ellipse for background) after background subtraction. Differential function is calculated from the 1-2 min interval data with tubular agents.

The recommended dose of furosemide (Lasix) in adults is 40 mg iv. In the standard protocol, Lasix is injected when the collecting system appears to be full (usually 15-20 min after tracer injection, called F +20). In patients with equivocal results, a second study with administration of Lasix 15 min before tracer injection (called F -15) is performed to maximise the diuretic stress which improves the sensitivity, specificity and reduces the chances of equivocal outcome (3,4). Quantitative parameters like time to peak (TTP), 20 min to peak activity ratio (20/MAX), pelvic T1/2 clearance time, parenchymal transit time (PTT) are valuble adjuvants (5).

The significance of the time-activity response patterns is based on correlations with both surgical results and long term clinical-follow-up. The literature is replete with attempts to refine and quantify response patterns. Conservatively, the diuresis renogram should be taken as only one indicator of drainage function. It has limitations. The results of diuretic renogram are affected by several factors: the urine flow rate (depends on renal function & level of hydration), large volume collecting system, increased pelvic compliance, rigid pelvis, immature kidney, degree of obstruction etc (2). Several attempts are made to standardize these variables in an ongoing effort to improve test accuracy (6,7,8,9).

Presently, diuretic renography is recommended as the initial screening study in patients found on urography or US to have dilated upper urinary tract without obvious cause (equivocal obstruction). It is also used in patients to determine the clinical significance of a known partial obstruction. It is well tolerated, easily repeatable, and appropriate for pediatric patients also. In patients with very poor renal function, patients with very dilated upper urinary tract or patients with equivocal diuretic renogram, Whitaker test can be useful and these tests should be regarded as complementary rather than competitive in evaluating equivocal obstruction (10).

References

1. Dubovsky E, Russell C. In Principles of Nuclear Medicine. Wagner H, Szabo Z, Buchanan J (eds), W.B Saunders Company, Philadelphia, PA, 1995. pp 977-978.

2. McBiles II M, Lambert A, Cote M, et al. Diuretic scintigraphy. Past, Present and Future. Nucl Med Ann 1995;pp185-216.

3. Upsdell SM, Testa HJ, Lawson RS, et al. Diuretic induced urinary flow rateat varying clearances and their relevance to the performance and interpretation of diuresis renography. Br J Urol 1988;61:14-18.

4. English PJ, Testa HJ, Lawson RS, et al. Modified method of diuresis renography for assesment of equivocal pelviureteric junction obstruction . Br J Urol 1987;59:10-14.

5. Britton KE, Nawaz MK, Whitfield HN, et al. Obstructive uropathy: Comparision between parenchymal transit time index and frusemide diuresis. Br J Urol 1987; 59: 127-132.

6. Conway JJ: Well-tempered diuresis renography: Its historical development, physiologic and thechnical pitfalls, and standardized technique protocol. Semin Nucl Med 1992;22:74-84.

7. Society of Nuclear Medicine. The "Well tempered" diuretic renogram: A standard method to examine the asymptomatic neonate with hydronephrosis or hydroureteronephrosis. J Nucl Med 1992;33:2047-2051.

8. O'Reilly PH. Diuresis renography. Recent advances and recommended protocols. Br J Urol.1992;69:113-120.

9. Consensus on Diuresis Renography for investigating the dilated upper urinary tract. O'Reilly PH, Aurell M, Britton K, et al. J Nucl Med 1996; 37:1872-1876.

10. O'Reilly PH, George, Weiss (eds). In Diagnostic Techniques in Urology. W.B. Saunders Company;1990:pp 401-425.

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J. Anthony Parker, MD PhD, Tony_Parker@bidmc.harvard.edu