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Figure 23. 99mTc-MAG3 scan in patient with severe acute tubular necrosis (ATN). Perfusion (A) is mildly imparied. The sequential images (B) show good uptake but excretion is greatly delayed and there is progressive accumulation of tracer in the kidney throughout the study. Ureteric obstruction is unlikely, because some activity does reach the bladder (though many transplant recipients have some residual function in their native kidneys which might be responsible for the bladder activity). If there is concern for obstruction, an ultrasound is usually helpful. The renogram curve (C) shows increasing activity in the transplant.

Figure 24. "Black hole sign". 99mTc-DTPA 1 minute sequential images of a left iliac fossa renal transplant 2 weeks post-op. This 44 year old woman initially had moderate acute tubular necrosis (ATN) after a cadaveric transplant. She developed acute rejection 1 week post-op and despite therapy progressed to renal infarction. The black hole sign (arrow) is almost always indicative of a non-viable kidney.

Figure 24. "Black hole sign". 99mTc-DTPA 1 minute sequential images of a left iliac fossa renal transplant 2 weeks post-op. This 44 year old woman initially had moderate acute tubular necrosis (ATN) after a cadaveric transplant. She developed acute rejection 1 week post-op and despite therapy progressed to renal infarction. The black hole sign (arrow) is almost always indicative of a non-viable kidney.

differential diagnosis includes hyperacute vascular rejection, vascular injury, ATN, urinary leak, and obstruction. Late causes include acute or chronic rejection, drug nephrotoxicity (particularly cyclosporine), transplant renal artery stenosis, obstruction, and recurrent primary disease. The role of nuclear imaging in investigating patients is similar to the non-transplant situation. It can be particularly useful in the immediate post-operative period when the patient is oliguric or anuric to differentiate vascular problems from ATN, and to exclude a urinary leak.

Procedure

As noted earlier, the transplanted kidney is located anteriorily in the iliac fossa and therefore the study is performed with the camera in front of the patient. The standard renogram is performed, with a flow phase and a renogram phase (Fig. 19).

Figure 25. Urine leak post-transplant. Following injection of 99mTc-MAG3, excreted activity is first seen along the medial and inferior margins of the transplant; by the end of the study it surrounds the graft.

Patient preparation is the same as for any other renogram—hydration is a primary consideration.

Interpretation

Studies performed in the first few days post-op will show varying degrees of harvesting injury. Harvesting injury is very common in cadaveric renal transplants. Living related donor transplants usually fare much better, and renograms can be normal from the early post-operative period. The typical finding is that of ATN with well-preserved perfusion relative to the level of functional impairment. The scintigraphic findings will differ depending upon the tracer used. A 99mTc-DTPA study will show good perfusion but poor uptake, high background levels and little or no excretion (Fig. 20). In the most severe cases, there will be a noticeable impairment of perfusion. If the first study is done on the first post-op day, subsequent studies done 1-3 days later usually show a drop in perfusion in moderate to severe ATN, presumably because of edema in the kidney. The perfusion findings will be the same with 99mTc-MAG3. Since 99mTc-MAG3 uptake is usually much better than 99mTc-DTPA uptake, the functional impairment usually manifests as prolonged transit through the kidneys with a picture of progressive parenchymal accumulation of tracer throughout the study (Figs. 21, 22 and 23). Severe cases may not show any

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