Vicarious liver visualization in solitary functioning kidney with technetium-99m ethylenedicysteine renal scintigraphy.

We present a case of 3-year-old boy who was incidentally diagnosed to have single left kidney on ultrasonography. Dynamic technetium-99m ethylenedicysteine renal scintigraphy was acquired for assessing the existing kidney function showed the tracer localization in bilateral renal fossae during the entire study. The single-photon emission computerized tomography/computerized tomography study revealed activity in the right renal fossa to be in the enlarged right lobe of the liver, which was mimicking as impaired functioning right kidney in planar images. The hybrid imaging helped in accurate delineation of tracer uptake by confirming it to be the false appearance of the right kidney in planar imaging. This case report also highlights the possible mechanism of renal tracer uptake in the liver parenchyma.

INTRODUCTION

The use of technetium-99m ethylenedicysteine (Tc99m-EC) as renal tracer agent had evolved on the observation that brain perfusion agent ethylenedicysteine dimer rapidly cleared through kidneys after being metabolized to ethylenedicysteine.[1] Since then, numerous studies have shown it to be a better renal agent than the already available renal agents like Tc-99m-mercaptoacetyltriglycine (MAG3) and I-131 orthoiodohippurate (OIH) because of its better excretion characteristics and image quality. It has a high first pass extraction of ~ 70%, low plasma protein (~30%) and ~ 5–6% red blood cell binding. The EC primarily gets excreted through the kidneys with minimal or negligible hepatobiliary excretion.[123] Now it has become the radiopharmaceutical agent of choice for assessment of renal function. Herein, we are reporting the unusual visualization of liver activity persisting throughout the dynamic as well in delayed phases in EC renal scan.

CASE REPORT

We present a case of 3-year-old asymptomatic male child subjected to renal dynamic imaging following incidentally diagnosed as having single left kidney on ultrasonography (USG) abdomen. The USG abdomen demonstrated normal sized and normally positioned left kidney while right kidney was not localized in the abdomen/pelvic region. Blood urea profile (26 mg/dL) and serum creatinine (0.8 mg/dL) were within normal limits. Renal dynamic scintigraphy was performed in posterior view under the gamma camera after intravenous administration of 2 mCiof Tc99m-EC along with 10 mg frusemide. From the initial frame onward, tracer activity was localized in both renal fossae, more intense in the renal left fossa. The activity in both renal fossae appeared to decrease with time and 3-h and 5-h delayed images showed faint tracer activity in bilateral renal fossae [Figure 1a–g]. The scintigraphic study was interpreted as normal functioning left kidney with unobstructed drainage and impaired functioning enlarged right kidney. The single-photon emission computerized tomography/computerized tomography (SPECT/CT) abdominal imaging [Figure 2a–d] was performed because of the nonvisualization of right kidney on USG; localized this tracer activity in the enlarged right lobe of liver.

Figure 1

Technetium-99 m ethylenedicysteine renal scintigraphy: (a) Flow images showed normal perfusion in left renal fossa and impaired perfusion in right renal fossa, (b) cortical uptake images revealed normal uptake in left kidney with pseudo-impression of impaired uptake in right kidney. Prevoid (c), postvoid (d), and delayed 3-h (e) static images showing the progressive tracer clearance from both renal fossa. Posterior (f) and anterior (g) images at 5-h showed mild tracer retention in the right renal fossa

Figure 2

Delayed single-photon emission computerized tomography/computerised tomography trans-axial (a and b) and coronal (c and d) images revealed tracer in the right lobe of liver instead of right kidney

DISCUSSION

The plasma clearance of any radiopharmaceutical takes place by different excretion pathways. However, hepatobiliary clearance of the renal agent should be minimal for accurate estimation of the effective renal plasma flow as significant hepatobiliary excretion may lower renal clearance values.[4] The OIH is the ideal reference agent for renal clearance but the technetium based agent like MAG3 is far from ideal replacement of OIH because of its high protein binding and low plasma clearance in human. The Tc99m-EC has efficient extraction fraction and excretion through the kidneys and is closer to OIH in function. It provides the high quality images due to negligible liver accumulation and high kidney to background ratio.[5] Different authors had shown significantly low accumulation of EC in the liver and intestine than that of MAG3 and OIH in animals as well as in human.[567] The lower liver activity makes EC particularly attractive in patients with renal failure. Prvulovich et al. reported better kidney delineation and only faint liver activity with EC compared to MAG3 in patients with severe renal failure.[2] Kibar et al. found EC images in pediatric patients to be of higher quality than MAG3 images.[8]

Certain factors have been described, affecting the excretion characteristics of MAG3. Nonfasting state in the patients undergoing MAG3 renal scintigraphy results in minimal or reduced GB uptake.[4] Apart from this, it has been shown that radiolabeled impurities are associated with hepatobiliary excretion of MAG3. Presence of oxidizing agents (sodium hypochlorite or hydrogen peroxide) in the sodium pertechnetate solution reduces the labeling.[9] Photolytic degradation and increased time spent in steps for MAG3 preparation may lead to impurities formation. Similarly, it has been shown that reconstitution with 10 ml of saline is optimal for high labeling efficiency while reconstitution with lesser amount of saline would result in the reduced labeling efficiency of Tc99m-MAG3.[10111213] The presence of different stereoisomers of EC in different kits may result in different excretion characteristics of EC.[14] It has been shown that the pretreatment with probenecid impairs the renal excretion of Tc99m-EC with more shifting toward hepatobiliary system and slower clearance from blood. Again there would be the presence of impurity in the EC kit, if labeling is done below pH of 12.[7] The unusual presence of tracer activity in the gall bladder (GB) has been described in a renal transplant patient undergoing EC renal scan.[15]

In the present case, the visualization of liver activity could not be attributed to radiochemical impurity as other renal scans done on the same day had not shown any altered bio-distribution. The patient in our case had normal renal function ruling out the reason of liver uptake due to impaired renal function. The initial perfusion images might have shown the liver activity in right abdominal region because of high blood flow to liver, but persistence of activity in the delayed image raised the suspicion for normally located impaired functioning enlarged right kidney.

The careful evaluation of the renal scan and sometime additional imaging acquired with SPECT/CT is essential before making the final interpretation. The present case highlights the unusual and rare EC uptake in liver in spite of the child having normal renal function, no history of drug intake affecting the renal clearance and no evidence of faulty radiopharmaceuticals on that day. It is assumed that the control of factors affecting the labeling efficiency may reduce the hepatic uptake and its excretion. Though we could not point out the exact reason for EC uptake in the liver, but have tried to point out the various reasons for the altered bio-distribution with review of the literature.

CONCLUSION

This rare case report showing presence of liver activity on EC renal scintigraphy required careful evaluation of renal scan and correlation with SPECT/CT before making the final impression.