Gall Bladder Activity on Technetium99m-Ethylenedicysteine Renogram Masquerading as Ectopic Kidney

Introduction

Technetium99m-ethylenedicysteine (^99mTc-EC) was first introduced as a potential renal tubular imaging agent alternative to technetium-99 m mercapto-acetyl-triglycine (^99mTc-MAG₃).[1] The hepatobiliary excretion of ^99mTc-EC is very low and usually does not affect image interpretation on routine imaging. However, the possibility of visualization of the gallbladder, which might mimic an ectopic kidney, should be kept in mind while reporting the ^99mTc-EC renogram study.[1] Here, we present an interesting case of a 4-year-old child suspected for ectopic right kidney in whom ^99mTc-EC renogram study was performed, and the scan revealed abnormal visualization of gallbladder simulating as an ectopic kidney.

Case Report

A 4-year-old male child presented with left loin pain and fever. On ultrasound abdomen, the right kidney was not visualized, and right ureterocele was present. The patient was referred for ^99mTc-EC renogram for localization of ectopic kidney, function, and subsequent drainage of kidneys. After intravenous administration of 1.4 mCi ^99mTc-EC with 10 mg furosemide, the patient was placed in supine position, and dynamic images were acquired using Symbia E dual head Gamma camera (Siemens).

Renogram study showed that the left kidney was normal in size and shape and located slightly inferior to normal position. Perfusion and initial dynamic images showed mildly reduced radiotracer uptake in renal parenchyma, with normal intrarenal transit time. Drainage into collecting system and subsequent clearance were appropriate, with increase in counts during delayed images and showing double peak which was suspicious for vesicoureteric reflux. The right kidney was not visualized in the right renal fossa [Figure 1].

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Figure 1

Posterior dynamic images of Technetium-99m-ethylenedicysteine renogram for a 4-year-old boy, suspected for hypoplastic/ectopic right kidney

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Delayed static images were acquired for 60 s on 128 × 128 matrix at 2 and 4 h postinjection [Figure 2]. There was focally increased tracer concentration in the right hypochondrium in delayed 2 h image and another focus of increased radiotracer concentration just below it. In view of suspected ectopic kidney, abnormal radiotracer localization in the right hypochondrium was initially thought as ectopic kidney and to confirm it a single-photon emission computed tomography (SPECT) CT scan was done. The abnormal foci of increased radiotracer uptake in the right hypochondrium corresponded to gallbladder and bowel on axial fused SPECT CT images [Figure 3]. With the aid of SPECT CT images, we were able to confirm the two abnormal foci of radiotracer concentration as gallbladder and bowel rather than ectopic kidney.

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Figure 2

(a and b) Immediate images after dynamic study (prevoid) both anterior and posterior. (c and d) 2-h delayed images. (e and f) 4-h delayed images. Delayed images showing hepatobiliary excretion (visualization of gallbladder and bowel)

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Figure 3

Fused SPECT/CT axial (a) and coronal (b) images shows abnormal radio tracer uptake in right hypochondrium corresponds to uptake in gall bladder on CT

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Discussion

^99mTc-EC has efficient extraction fraction and excretion through the kidneys and is closer to ^99mTc-MAG₃ in function.[12] It provides high-quality images due to negligible liver accumulation and high kidney to background ratio.[12] Different authors had shown significantly low accumulation of ^99mTc-EC in the liver and intestine than that of ^99mTc-MAG₃ in animals as well as in humans.[3] The lower liver activity makes ^99mTc-EC particularly attractive in patients with renal failure.[4] The presence of different stereoisomers of ^99mTc-EC in different kits may result in different excretion characteristics of EC.[3]

However, the visualization of gallbladder with non-hepatobiliary radiopharmaceuticals was also reported in many studies, and it was not always pathological.[1] Previous authors had documented hepatobiliary excretion of ^99mTc-EC as a region of normal biodistribution of the tracer.[12] Another cause for altered biodistribution of a radiopharmaceutical was thought to be as a result of its low radiochemical purity.[15] Gallbladder visualization in the present study cannot be attributed to the quality of ^99mTc-EC because gallbladder activity was not seen in any other patient injected with the same preparation of ^99mTc-EC on the same day.

Arora et al. reported a case of dual cadaveric renal transplant, who underwent an EC renogram and showed incidental uptake in gallbladder on delayed images, confirmed on SPECT/CT images.[1]

Jain et al. reported a case with liver uptake on EC renogram. The initial perfusion images showed liver activity in the right abdominal region, which was thought to be due to high blood flow to the liver, but persistence of activity in the delayed image raised the suspicion for normally located impaired functioning enlarged right kidney. SPECT CT images acquired had confirmed the radiotracer localization in liver.[2]

Conclusion

The possibility of visualization of the gallbladder should be kept in mind while reporting the ^99mTc-EC renogram. It might masquerade an ectopic kidney; hence, such cases need to be interpreted with caution.