Extrarenal distribution of Tc-99m ethylenedicysteine in dynamic renal scintigraphy and its potential implications on scan interpretation

Extra-renal activity of Tc-99m EC on dynamic renal scintigraphy may result in interpretation pitfalls and dilemma. This case series demonstrates extra-renal distribution of Tc-99m EC and its potential clinical implications. Sterile formulation kit for reconstitution with sterile Tc-99m sodium pertechnetate eluted from Molybdenum-99/ Tc-99m generator was used for Tc-99m EC preparation. Dynamic images of the abdomen in posterior view were acquired immediately after intravenous administration of recommended dose of Tc-99m EC on dual headed gamma camera with SPECT/CT system (GE Discovery NM/CT 670 DR). Furosemide was injected intravenously immediately or 10 minutes following radiotracer administration. Other views and/or SPECT/ CT were acquired in selected cases. Correlation with clinical, biochemical, and other available imaging findings was also done. Tc-99m EC dynamic renal scintigraphy findings in four cases are described. Case 1: A 34-year-old woman with history of right pyeloplasty. Dynamic images did not reveal dilated ureter. Delayed images at 2 and 4 hours revealed tracer uptake in the region of right ureter. This was due to tracer activity in the bowel (more prominent in anterior views). CT urography also did not reveal dilated ureter. Potential pitfall here is possible perception of bowel activity as ureteric activity. Case 2: A5- year-old girl with enlarged and hydroureteronephrotic left kidney. Right kidney was not visualized in dynamic images. Tracer activity is noted in the right upper quadrant region and lower right renal fossa, corresponding to liver, gallbladder and bowel activity. Such pattern may falsely appear as faintly visualized right kidney and dilated ureter. Case 3: A 3-year-old girl with pelvic pancake kidney and right pelviureteric-junction obstruction showed severely impaired perfusion and cortical tracer uptake in the right moiety of kidney. Delayed images at 2 and 4 hours showed an additional site of tracer uptake in the region of right renal fossa. Tc-99m DMSA scan revealed no renal tissue in the right renal fossa. Such distribution in a patient with single kidney may create illusion of poorly functioning second kidney. Case 4: A 45-year-old-man with bilateral nephrolithiasis. Dynamic images showed small sized kidneys with impaired cortical tracer uptake. Delayed images at 2 and 4 hours also showed tracer uptake along the superolateral aspect of right kidney which on SPECT/ CT images localized to abnormal tracer uptake within the gall bladder. Reporting errors may arise due to extra-renal activity in close proximity to the kidney. Extrarenal tracer distribution of Tc99m-EC may cause interpretation pitfalls especially when in close proximity to the organs of urinary tract. This may arise due to alternate route of hepatobiliary excretion, and other factors related to radiopharmaceutical preparation or patient (interference with drugs, renal failure). Interpretation may become even more challenging in severely impaired renal function with high background activity. Correlation with additional views, SPECT/CT, clinical profile, renal function tests and findings of other imaging modalities is essential in these cases. (author)