Sharp peaks in the downslope phase of the diuresis renogram

GAMUTS Edited by Robert C. Stadalnik

Sharp Peaks in the Downslope Phase of the Diuresis Renogram R. Valkema, C.N. Boot, and E.K.J. Pauwels

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16-YEAR-OLD GIRL was referred for evaluation of renal parenchymal function and possible obstruction of the right system. At 2 years of age she had undergone reimplantation of both ureters for bilateral reflux and recurrent urinary tract infections. At 10 years of age urethrotomy had been performed because of stenosis and recurrent infections. At that time no reflux could be shown with contrast cystography or radionuclide cystography. Serial ultrasound studies during follow-up after urethrotomy suggested some dilation of the left and progressive dilation of the right ureter. Renography was requested for the evaluation of possible obstruction and concurrent functional impairment. Scintigraphy was performed 30 minutes after ingestion of 400 mL water. The patient was supine during the study. After intravenous (IV) injection of a bolus of 70 MBq (1.9 mCi) [99mTc]mercaptoacetyltriglycine ([99mTc]MAG3) in a left antecubital vein, posterior images of 1 minute were obtained over 25 minutes with an analog gamma camera (GCA 40A, Toshiba, Japan). The camera was connected to a generalpurpose nuclear medicine computer system (Medical Data Systems A 2, Ann Arbor, MI). Dynamic acquisition started with 120 frames of 1 second immediately after injection, followed by 90 frames of 20 seconds. Total study duration was thus 32 minutes. Renography curves were generated for the entire 32 minutes of the study and for the first 2 minutes separately. Curves over the cortical regions of the kidneys also

From the Department of Diagnostic Radiology and Nuclear Medicine. University Hospital Leiden. The Netherlands. Address reprint requests to Professor Dr E.K.J. Pauwels. Department of Diagnostic Radiology and Nuclear Medicine, University Hospital Building 1. C4Q, PO Box 9600, 2300 RC Leiden, The Netherlands. Copyright 9 1994 by W..B. Saunders Company 0001-2998/94/2404-0006505. 00/0 350

were generated. In the 17th minute, 20 mg furosemide was administered IV in a right antecubital vein after attempting to administer it in the same vein that was used for injection of the radiopharmaceutical. The serial images showed normal function of both kidneys without signs of obstruction. The right kidney was smaller than the left, without specific defects. On the images obtained after 15 minutes postinjection, increased activity in the parenchyma of both kidneys was noted, with a maximal intensity in the 18th minute, followed by increased excretion afterward (Fig 1). The renography curves were normal for both kidneys until 15 minutes. Thereafter, the curves started to increase sharply and simultaneously, with a second peak at 18 minutes followed by a rapid decline. A similar pattern was seen on the cortex curves (Fig 2). DISCUSSION

The serial images suggested that a second amount of [99mTc]MAG3 had entered the circulation, with extraction by the renal parenchyma and subsequent excretion. The patterns of the curves resemble a second (normal) renogram superimposed on the first. Furthermore, the start of the second peak occurred at the time of attempted IV administration of furosemide in the left antecubital region. Therefore, we concluded that initially a considerable amount of [99mTc]MAG3 remained at the site of injection. It must have entered the circulation rapidly while the left elbow was manipulated. This hypothesis implies that the remaining amount of radiopharmaceutical was already in the vein when the elbow was manipulated, presumably since the first injection. It is our routine to put a gauze bandage firmly over the injection site immediately after the injection. Intravenous stasis may be explained by the presence of a valve distal to the compressed

Seminars in Nuclear Medicine, Vol XXIV, No 4 (October), 1994: pp 350-353

SHARP PEAKS IN THE RENOGRAM

Fig 1. Posterior 20-second images taken 14 (left) and 16 minutes (right) after injection of 70 MBq [~mTc]MAG3 IV in a left antecubital vein. At 14 minutes, residual activity in the left elbow region is just visible on the edge of the image. After manipulation at 16 minutes this activity has disappeared, whereas increased activity can be seen in the parenchyma of both kidneys and in the background.

injection site so that a part of the injected bolus remained there. An extravascular depot could not have entered the circulation rapidly enough to cause this pattern. Occasionally, a transient small increase in activity is observed immediately after furosemide administration, probably caused by diuresis-induced accumulation of activity (double hump). ] This normal variant is seen with good renal parenchymal function. In the present case, both the shape and size of the second peak as well as the findings on the serial images (Fig 1) were inconsistent with this normal variant. Diuresis renography is applied in patients with hydronephrosis or hydroureteronephrosis to distinguish dilation without obstruction from significant mechanical obstruction. 1-5 The usual renogram patterns of dilation without obstruction and of moderate or significant mechanical obstruction have been described before 1,3,6 and are well known. Occasionally, the renograms contain abnormalities in the downslope phase, which may reflect a pathologic condition or may be caused by an artifact. The shape of the abnormalities in the curves and whether the findings are unilateral or bilateral and asymmetric or symmetric are important clues in assisting in the differential diagnosis. Often close examination of the serial images is vital for the correct diagnosis. Movements of the patient during the study can cause sudden steep changes in the curves of both kidneys simultaneously. These artifacts can be recognized from the serial images and

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corrected either by manual or automatic methods. 7 Sudden increases in abdominal pressure using the Valsalva maneuver may cause sharp bilateral spikes on the curves. Coughing can cause a combination of motion and pressure artifacts. Vesicoureteric reflux of grade II and higher 8 can cause sawtooth waves on the downslope part o f the renogram. 9 The condition is generally unilateral, but it can be bilateral in 44% of cases. I~ In cases of bilateral vesicoureteric reflux the abnormal waves in the curves are likely asymmetric. Inspection of the serial images or a time-activity curve over the bladder can identify vesicoureteric reflux as the cause of these waves in indiVidual patients. This phenomenon is the basis of indirect radionuclide cystography for t h e diagnosis of vesicoureteric reflux.~1With incomplete duplication of the ureters from one kidney, reflux from one system into

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Fig 2. Renogram curves over the kidney regions (left) and cortex regions (right). The curves rise simultaneously after manipulation of the left elbow in the 16th minute of the study.

VALKEMA, BOOT, AND PAUWELS

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the other can occur. Separate renograms over the upper-and t e w ~ ~ e t i c s - e f the ~ a l kidney can show small complementary sawtooth waves in the curves. 11 A gradual secondary increase or subtle waves in the renogram curve can be caused by several conditions, especially with low urinary flow rates. Sudden hypotension during the procedure is a rare cause of bilateral decrease of urinary flow. Stepwise elimination9 from the kidney can be seen with dehydration; the abnormalities in the curves will likely be bilateral but asymmetric. Increased resistance in any part of the collecting system and ureters may result in a mismatch between tracer influx and capacity, causing temporary increases in the renogram curve. A full and distended bladder may slow the emptying of the collecting system, even in the absence of reflux,5A2 with bilateral but generally asymmetric abnormalities in the renogram. Voiding before the study is required, and sometimes catheterization will be necessary. Collecting system abnormalities generally are unilateral. Pyelonephritis, secondary scarring after passage of calculi, and neoplasms are a few of the possible causes. Extrinsic pathology such as retroperitoneal fibrosis or lymph nodes may compromise passage through one or both ureters. Passage can be impaired depending on position. An obstructive renogram may show drainage after change of position (eg, from supine to prone or sitting). 5,13 This has been reported for severe hydroureteronephrosis (prune-belly syndrome and posterior urethral valves). 13 Recently, Rossleigh et al advocated the use of an additional image after gravityassisted drainage in selected cases. 14With intermittent hydronephrosis, the ureteropelvic junc-

tion can become self-obstructing with forced dkiresis, resulting in a eharaete~tie secondary gradual peak in the renogram, designated the "double peak sign" by Homsy et al. 4,6 Patients in whom this sign is shown have a tendency for progression to frank obstruction within a few months to a few years.6 Following are the conditions associated with a rising renogram curve after the normal peak: COMMON

1. Movement artifacts (sharp, bilateral, symmetric) 7 2. Dehydration with stepwise elimination (gradual, mostly bilateral, asymmetric)9 3. Vesicoureteric reflux (sharp, predominantly unilateral) 9,u UNCOMMON OR RARE

1. Furosemide accentuated diuresis, "double hump" (small, bilateral, symmetric)1 2. Ureteroureteric reflux (sharp, mostly unilateral) 11 3. Postural (unilateral or bilateral, asymmetric)5,13 4. Collecting system abnormalities (mostly unilateral) 5: Intermittent hydronephrosis (mostly unilateral, gradual) 4,6 6. Sudden hypotension during procedure (bilateral, symmetric) 7. Valsalva maneuver (sharp, bilateral, symmetric) 8. Artifact from second bolus (sharp, bilateral, symmetric)* *The present case.

REFERENCES 1. Thrall JT, Koff SA, Keyes JWi Diuretic radionuclide renography and scintigraphy in the differential diagnosis of hydroureteronephrosis. Semin Nucl Med 11:89-114, 1981 2. Kass EJ, Fink-Bennet D: Contemporary techniques for the radioisotopic evaluation of the dilated urinary tract. Uroi Clin North Am 17:273-289, 1990 3. O'Reilly PH, Lupton EW: Obstructive uropathy, in O'Reilly PH, Shields RA, Testa HJ (eds): Nuclear Medicine in Urology and Nephrology (ed 2). London, Butterworths, 1986, pp 91-108 4. O'Reilly PH: Diuresis renography. Recent advances and recommended protocols. Br J Urol 69:i13-120, 1992

5. Sakar SD: Diuretic renography: Concepts and controversies. Urol Radiol 14:79-84, 1992 6. Homsy YL, Mehta PJ, Huot D, et al: Intermittent hydronephrosis. A diagnostic challenge. J Uroi 140:12221226, 1988 7. De Agostini A, Moretti R, Bellett! S, et al: A motion correction algorithm for an image realignment programme useful for sequential radionuclide renography. Eur J Nucl Med 19:476-483, 1992 8. Lebowitz RL, Olbing H, Parkkulainen KV, et al: International system of radiographic grading of vesicoureteric reflux. Pediatr Radiol 15:105-109, 1985

SHARP PEAKS IN THE RENOGRAM

9. O'Reilly PH, Shields RA, Testa HJ: Renography, in O'Reilly PH, Shields RA, Testa HJ (eds): Nuclear Medicine in Urology and Nephrology (ed 2). London, Butterworths, 1986, pp 9-25 10. van den Abbeele AD, Treves ST, Lebowitz RL, et al: Vesicoureteral reflux in asymptomatic siblings of patients with known reflux: Radionuclide cystography. Pediatrics 79:147-153, 1987 11. Bevis CRA: Reflux studies, in O'Reilly PH, Shields RA, Testa HJ (eds): Nuclear Medicine in Urology and Nephrology (ed 2). London, UK, Butterworths, 1986,pp 37-48

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12. Berdon WE, Baker DH: The significance of a distended bladder in the interpretation of intravenous pyelograms obtained on patients with "hydronephrosis." Am J Roentgenol 120:402-409, 1974 13. Shore RM, Uehling DT, Bruskewitz R, et al: Evaluation of obstructive uropathy with diuretic renography. Am J Dis Child 137:236-240, 1983 14. Rossleigh MA, Leighton DM, Farnsworth RH: Diuresis renography. The need for an additional view after gravity-assisted drainage. Clin Nucl Med 18:210-213, 1993