Abstract
The treatment plan and the decision for surgery in a significant proportion of patients with pelvi-ureteric junction (PUJ) obstruction type of hydronephrosis are dependent on the findings of renal scintigraphy. We report a case of a 3.5-year-old girl with right-sided PUJ obstruction, wherein the tracer excretion into the cecum and ascending colon complicated the clinical picture thereby misleading the final diagnosis or treatment plan and blurring the distinction between hydronephrosis and hydroureteronephrosis. Additional investigations may be required in such cases to reach a conclusion. The authors considered reporting this case in view of the deep-rooted clinical implications toward making a correct diagnosis. Besides, the possible mechanisms to explain the presence of the tracer inside the bowel have been discussed.
KEYWORDS: 99mTc-L, L-ethylene dicysteine, bowel excretion, extrarenal clearance, hepatobiliary clearance, L, L-ethylene dicysteine, pelvi-ureteric junction obstruction, renal scintigraphy
INTRODUCTION
Renal dynamic scan (RDS) or scintigraphy is the most widely used noninvasive test to determine the severity and functional significance of pelvi-ureteric junction (PUJ) obstruction. The decision for surgical intervention in a significant proportion of these patients is based on the findings of this single investigation.
The authors hereby report a case of right-sided PUJ obstruction, wherein the presence of tracer inside the cecum and ascending colon masquerading as dilated ureter has the potential to complicate the clinical picture and mislead the final diagnosis or treatment plan.
CASE REPORT
A 3.5-year-old girl presented with nonspecific right flank pain of recent origin. Systemic examination including the abdomen was unremarkable. Sonography was suggestive of right-sided PUJ obstruction (right hydronephrosis with a nondilated ureter).
The patient underwent RDS with 99mTc-L, L-ethylene dicysteine (99mTc-LLEC) to determine the renal clearance, functional significance of PUJ obstruction, and differential renal function. 3 mCi of activity was administered as a bolus. Differential function assessed between 1–2 min after the tracer injection with background correction was equivocal (Lt: 52% vs. Rt: 48%). Transit of tracer through the kidney was assessed with Tmax (Lt: Rt = 1.8:15.3 s) and inspection of the renogram curve [Figure 1a]. The left renal curve was typically normal, while the right curve was ascending continuously and represented delayed excretion.
Figure 1.
(a) Renal dynamic scan done with intravenous administration of 3 mCi 99mTc-L, L-ethylene dicysteine reveals normal renogram curve on the left and ascending curve on the right, consistent with right pelvi-ureteric junction obstruction. (b) Delayed 4-h static image (posterior: the left kidney seen on the left and the right kidney on the right) of a 99mTc-L, L-ethylene dicysteine renal dynamic scan, showing normal left kidney (reniform shape may be appreciated) and minimally enlarged hydronephrotic right kidney (with tracer retention as compared to contralateral side). There is a continuous extension of tracer activity from the inferior pole region of the right kidney toward the bladder in the region of the right ureterovesical junction
However, the delayed (4 h) renal static image was peculiar with the presence of radioactivity caudal to the lower pole of the right kidney, giving the appearance of dilated ureter [Figure 1b]. The possibility of the gut activity was also considered.
A repeat sonogram was requested to resolve the disparity between the ultrasonography (hydronephrosis with nondilated ureter) and RDS (hydroureteronephrosis) findings. The right kidney was hydronephrotic (SFU grade 3; cortical thickness 6 mm) with abrupt tapering at the level of PUJ [Figure 2a]. Transverse imaging at the levels of lower pole (right kidney) and bladder trigone confirmed the presence of nondilated upper/mid-ureter [Figure 2b] and nondilated distal ureter [Figure 2c], respectively.
Figure 2.
(a) Ultrasound image of the right kidney (along its long axis) showing dilated pelvicalyceal system (SFU Grade 3) with abrupt tapering at the level of pelvi-ureteric junction (arrow). (b) Transverse image at the level of lower pole showing that the upper/mid-ureter is not dilated. (c) Transverse ultrasonography image at the level of bladder trigone showing normal insertion of ureters at vesicoureteric junction (arrow) and there is no dilatation of distal ureters
Rereview of the RDS images confirmed that the abnormal radioactivity in the right lower quadrant was generated by the tracer in the cecum and ascending colon.
DISCUSSION
Today, 99mTC-EC has become the scintigraphy agent of choice for assessment of renal function and RDS the investigation of choice for evaluation of patients with PUJO type of hydronephrosis.
99mTc-LLEC is the terminal metabolite of 99mTc-LLEC-diethyl-ester (99mTc-LL-ECD) used for a brain scan. LLEC is excreted rapidly and efficiently into the urine. It has a high first-pass extraction (~70% vs. 20% for 99mTc-diethylenetriaminepentaacetic acid), low plasma protein binding (~30%), and low red blood cell binding (~5.7%) in addition to negligible extrarenal clearance and high kidney-to-background ratio.[1] Several studies in both animals and human subjects have reported on the significantly low accumulation of LLEC in the liver and intestines vis-a-vis its contemporary agents (MAG3/OIH).[2,3]
In the index case, the visualization of tracer in the cecum and ascending colon can only be explained by extrarenal clearance of LLEC. PubMed search revealed two case reports[4,5] mentioning extrarenal clearance of LLEC. Arora et al. have reported the vicarious visualization of the gallbladder on 99mTc-EC scan in a 10-year-old patient of renal transplant.[4] Jain et al. have reported the presence of liver activity on LLEC-renal-scintigraphy mimicking an impaired functioning kidney in an empty right renal fossa.[5]
We have reviewed the available literature on LLEC and the excretion characteristics of other radiopharmaceuticals and made certain observations.
First, the radiochemical impurities may alter the biodistribution of any radiopharmaceutical, especially if labeling is done below a pH of 12. However, in such a situation, the other cases of RDS performed simultaneously should demonstrate similar activity.
Second, ~10% of hepatobiliary clearance has been reported for 99 mTc-MAG3. Paradoxically, the lack of hepatobiliary excretion is an advantage of LLEC over MAG3.
Third, the different stereoisomers of EC may have different excretion characteristics.[5]
Fourth, low-level hepatic uptake of LLEC (<6%) has been reported in patients with anuria.[4] In case of normally functioning kidneys, the hepatic uptake may not be obvious due to high emission from the kidneys.
Fifth, pretreatment with probenecid impairs the renal excretion of LLEC, resulting in reduced urinary tracer excretion along with a more pronounced hepatobiliary handling of EC and a slower clearance from the blood. There is no history of any drug intake impairing renal excretion in the index case. The disease pathology (PUJ obstruction) may not be blamed per SE in view of normal contralateral kidney and consistent absence of gut activity in patients with PUJ obstruction.
In our index case, it is not possible to figure out the exact reason for visualization of contrast inside the cecum and ascending colon with the available knowledge. However, the possibility of hepatobiliary excretion of the tracer soon after injection seems likely. The blood level of the tracer is maximum soon after injection; it declines rapidly thereafter. The localization of this contrast in the gallbladder and its transportation into the cecum/ascending colon is expected to take time which correlates with its visualization in the delayed (4-h) images.
The authors considered reporting this case important because of its clinical implications in making a correct diagnosis. The gut activity may be misinterpreted as a dilated ureter, and the distinction between hydronephrosis and hydroureteronephrosis may be blurred. This may complicate the clinical picture and mislead the treatment plan.
CONCLUSION
With a background of available clinical information, a careful interpretation of the renal scan is usually sufficient to reach a meaningful conclusion; however, additional imaging such as correlation with ultrasonography or single-photon emission computed tomography (CT)/CT may occasionally be considered essential.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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