British Journal of Radiology (2005) 78, 349-352
© 2005 British Institute of Radiology
doi: 10.1259/bjr/30076658
The absent kidney in 99Tcm-MAG3 renogram: a dramatic reversible consequence of contrast nephrotoxicity superimposed on renal obstruction
I Kayani, FRCR,
A M Groves, FRCR,
R Syed, FRCS,
N Nagabushan, MRCP,
F Pakzad, MRCS,
E M Prvulovich, MSc, MD and
J B Bomanji, MB BS, MSc, PhD
Institute of Nuclear Medicine, Middlesex Hospital, Mortimer Street, London W1T 3AA, UK
Correspondence: Dr Jamshed B Bomanji
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Abstract
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99Tcm-mercaptoacetyltriglycine (MAG3) renogram is a robust imaging technique used to delineate upper urinary tract obstruction. The changes observed on the renogram are often reversible on relief of obstruction. We present two cases illustrating the extreme consequence of contrast nephrotoxicity on pre-existing obstructed kidneys. In one case, this led to severe impairment of perfusion and uptake observed on 99Tcm-MAG3 renogram and in the second case virtual non-visualization of the obstructed kidney. Subsequent treatment of obstruction, led to dramatic improvement in renal function. It is important for clinicians, nuclear medicine physicians and radiologists to be aware of the potential of contrast nephrotoxicity in obstructed kidneys.
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Introduction
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99Tcm-mercaptoacetyltriglycine (MAG3) is an integral part of investigation in patients with suspected upper urinary tract obstruction [1–3]. The 99Tcm-MAG3 renogram helps confirm obstruction, estimate differential renal function and monitor the success of interventional procedures to relieve obstruction. As part of pre-intervention assessment, patients may receive intravenous (IV) contrast, usually for intravenous urogram (IVU) examination or less commonly during CT angiogram for the assessment of pelviureteric junction (PUJ) obstruction. There is a well-documented risk of nephrotoxicity following administration of IV contrast media [4–6]. This is rare (less than 2%) in patients with normal renal function but occurs in up to 25% of patients with predisposing conditions [5, 6]. Contrast nephrotoxicity may be superimposed on changes owing to urinary obstruction in the 99Tcm-MAG3 renogram.
We present two cases where severe but reversible unilateral renal impairment occurred following intravenous contrast administration.
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Case one
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A 73-year-old female was admitted for further investigation and treatment of right pelviureteric obstruction. There was a history of intermittent right loin pain and urinary tract infection but during the course of admission she remained clinically well and asymptomatic. A 99Tcm-MAG3 renogram performed at her referring hospital 1 month prior to admission had demonstrated reduced perfusion of the right kidney compared with the left kidney, with right cortical tracer retention and 37% of total function in right kidney.
Further assessment with a CT angiogram (Siemens Somatom Plus 4 Volume Zoom, Forcheim, Germany) with 130 ml of Iohexol (300 mg Iodine ml–1) was performed. This showed normal cortical thickness but reduced perfusion of the right kidney with the right renal artery stretched over a dilated right renal pelvis (Figure 1
). A 99Tcm-MAG3 scan 4 days later (Figure 2a) showed virtually no tracer activity in the right kidney and a normal left kidney. 2 days later a Doppler ultrasound confirmed perfusion of the right kidney but with an elevated resistive index (RI) of 0.88. A repeat 99Tcm-MAG3 scan (Figure 2b), performed the following day (8 days post CT angiogram) showed tracer uptake in the right kidney with a prolonged nephrogenic phase of activity and a differential function of 17%. A week later, a retrograde ureterogram confirmed a right PUJ obstruction and a ureteric stent was placed. Ureteric brushings were negative for malignancy on cytological examination.
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Figure 1. Case 1: CT arterial phase renal angiogram (Siemens Somatom Plus 4 Volume Zoom, Forcheim, Germany). Coronal multiplanar reconstruction image; there is clear reduction in perfusion (enhancement) of the right kidney and gross dilatation of the renal calyces.
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Figure 2. Case 1: (a) 99Tcm-MAG3 renogram 4 days post CT angiogram. The right kidney appears to be absent, no tracer uptake can be identified in the right kidney. (b) Follow up renogram 2 days later, shows a poorly perfused right kidney with prolonged nephrogenic phase of activity. (c) 99Tcm-MAG3 renogram 6 weeks later following ureteric stent placement shows good perfusion, significant recovery of function and rapid excretion of tracer.
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A 99Tcm-MAG3 scan performed 7 weeks after ureteric stent placement (Figure 2c
) showed significant recovery of right-sided renal perfusion and function with good excretion of tracer. The right kidney now contributed 30% of total renal function. Further 99Tcm-MAG3 follow-up studies have shown no change in differential function or outflow pattern of tracer from the right kidney.
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Case two
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A 61-year-old man with Parkinson's disease presented with intermittent loin pain over several weeks, microscopic haematuria and normal serum urea and electrolytes. An IVU (70 ml 300 mg ml–1 Iohexol) showed a left nephrogram but no left sided contrast excretion. The right renal tract was normal. A further bolus of 70 ml Iohexol 300 mg l–1was given (total dose 140 ml 600 mg l–1), but despite the second dose subsequent films failed to show any contrast excretion from the left kidney with a persistent left nephrogram on a delayed 72 h film. An ultrasound, performed on the same day revealed only mild pelvicalyceal dilatation (anteroposterior (AP) pelvis diameter 1.1 cm).
The patient remained clinically well but 72 h post-IVU the serum urea and creatinine rose to 148 µmol l–1 and 9.2 mmol l–1, respectively. A 99Tcm-MAG3 renogram (5 days post IVU) was performed to further evaluate the left kidney (Figure 3a). The left kidney was poorly perfused with poor uptake and virtually no excretion of tracer and a divided renal function of less than 10% in the left kidney. The right renal appearance and uptake was within normal limits.
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Figure 3. Case 2: (a) 99Tcm-MAG3 renogram 5 days after high dose urography demonstrates severe reduction in perfusion and function of left kidney with no excretion of tracer. (b) Follow up renogram 6 weeks post placement of left nephrostomy (arrows); there is improved perfusion of left kidney, dramatic improvement in left renal function and normal excretion of tracer.
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A nephrostomy was placed in the left kidney and a subsequent contrast enhanced CT scan of the abdomen revealed retroperitoneal fibrosis as a likely cause of urinary obstruction. The fibrosis was probably induced by pergolide prescribed for Parkinson's disease. Urea and electrolytes normalized within 10 days of the nephrostomy and a repeat 99Tcm-MAG3, 6 weeks later (Figure 3b) showed good, almost symmetric perfusion of the left kidney with brisk excretion of tracer. The left kidney contributed 37% to the total renal function compared with 10% pre-nephrostomy.
The patient underwent bilateral ureterolysis (surgical release of ureter by blunt dissection). During the procedure a retroperitoneal biopsy was performed which was consistent with retroperitoneal fibrosis. Follow-up over 4 years with yearly 99Tcm-MAG3 renograms have shown no change in differential function or outflow pattern of tracer from the left kidney.
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Discussion
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Unilateral, reversible, shutdown of renal perfusion is an uncommon occurrence in clinical practice. In the two cases we describe, there were some common features, which could have caused rapid loss of renal function. Both patients were exposed to intravenous contrast and their kidneys were already incompletely obstructed secondary to a unilateral PUJ obstruction in case 1 and retroperitoneal fibrosis in case 2. It is likely that both patients had an acute on chronic renal insult, which led to virtual unilateral renal shutdown.
The one common trigger, which led to this chain of events, was the intravenous administration of a rapid and large volume iohexol contrast bolus. A number of mechanisms are responsible for contrast nephrotoxicity [5, 7, 8]. Contrast media induced diuresis leads to increased tubular and interstitial pressure leading to compression of small renal vessels. Contrast media stimulate the release of endothelin and also induce aggregation of red blood cells. The net effect of these changes is to reduce renal blood flow. In addition diuresis causes increased metabolic activity of tubular cells leading to medullary hypoxia and contrast media have a direct cellular toxic effect [5]. Contrast nephrotoxicity is exaggerated in the presence of volume depletion and pre-existing renal impairment [5, 6]. The classical pattern of contrast-induced nephrotoxicity on a 99Tcm-MAG3 study (which is dominantly secreted by the tubules) mimics acute tubular necrosis and involves both kidneys. The 99Tcm-MAG3 scan shows reduced perfusion of the kidneys coupled with tracer accumulation in the renal parenchyma and virtually no excretion of activity [9, 10]. It is uncommon to observe such a pattern in one kidney only.
It could be argued that acute renal obstruction could have caused rapid loss of renal perfusion and that it was not due to contrast in both cases. It has been shown that acute urinary obstruction is associated with reduction in medullary renal blood flow, with apoptosis of tubular cell as early as 2 h post ureteral ligation [7]. The second case illustrates the changes expected with severe obstruction (Figure 3). There was reduced perfusion and uptake of 99Tcm-MAG3 with non-visualization of the intrarenal and extrarenal tract and virtually no drainage from the kidney even after frusemide diuresis (40 mg IV, bolus). This was depicted graphically as a rising time-activity curve. However, reduction in perfusion does not lead to a virtual absence of activity on an isotope renogram, unless there is a second superimposed renal insult. In case two, superimposed contrast induced nephrotoxicity would explain the transient unilateral renal shutdown. The patient had undergone high dose urography a few days prior to the 99Tcm-MAG3 renogram and had evidence of contrast induced nephrotoxicity with a subsequent rise in serum urea and creatinine. Indeed there is experimental evidence that contrast media exacerbates medullary ischaemia in obstructed kidneys [7]. In the first case, non-visualization of the kidney on 99Tcm-MAG3 renogram (Figure 2a) was more extreme and beyond the changes expected with classic severe obstructive nephropathy. Interestingly, the patient had suffered no clinical symptoms in the interval between the initial 99Tcm-MAG3 (done 1 month prior to the CT angiogram) and the 99Tcm-MAG3 demonstrating absent right renal perfusion. It is reasonable to attribute the severe decline in renal perfusion post CT angiogram, at least in greater part to contrast induced nephrotoxicity. There were two risk factors for contrast nephrotoxicity; pre-existing renal impairment and age >70 years [11, 12]. Another possible compounding factor in this case, was the presence of urinary obstruction [7, 8]. It is also possible, that the marked renal pelvis dilation impaired renal blood flow in the overlying stretched renal arteries. These vessels have been implicated as markers of surgical failure, and can cause or worsen PUJ obstruction [13–15].
Predicting functional recovery from contrast induced nephrotoxicity and obstruction is difficult and may take a few days to several weeks. It has been suggested that it is best to allow an interval of at least 2 weeks after IV contrast medium administration to ensure changes are not due to contrast media [1]. In case two the improvement in function of the involved kidneys, 6 weeks post-stent insertion was probably due to resolution of obstruction and recovery from contrast induced nephrotoxicity. This is a more likely outcome in the context of normal renal cortical thickness demonstrated on the CT scan in both cases. Niemczyk et al [16] used the 99Tcm-MAG3 renogram to evaluate patients undergoing endopyelotomy for PUJ obstruction and found no improvement in post-operative function when function prior to surgery was less than 30%. Gupta et al [15] found the success rate for open pyelotomy in PUJ obstruction reduced from 80% to 54% for patients with renal function of 25–40% versus function of less than 25%.
Our cases highlight a relatively common clinical scenario. Patients presenting with urinary obstruction often receive IV contrast media in addition to NSAIDs (non steroidal anti inflammatory drugs). There is compelling evidence that the usage of NSAIDS and IV contrast agents results in cumulative renal insult [7]. On this basis caution has been advised over the usage of contrast in patients with urinary obstruction [8]. Documented clinical cases have, however, been lacking. Our cases provide some clinical data to back up the experimental evidence and reinforce the message that caution should be exercised over the usage of contrast media in this scenario. In particular large volumes of intravenous contrast in patients with severe upper urinary tract obstruction can lead to virtually absent perfusion of the involved kidney. Fortunately the potential of significant improvement in renal function following timely treatment is good.
Received for publication July 15, 2004.
Revision received November 10, 2004.
Accepted for publication December 6, 2004.
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Abstract
Introduction
