The renal transplant score: A different way of evaluating renal transplant pathology

The renal transplant is a notoriously difficult organ to assess for pathology. Radionuclide imaging can help, but, although sensitive, the evaluation is not very specific. For this reason, a different approach was used to examine renal images and results were correlated with histology. The transplant score is determined from images of perfusion and function on certain criteria such as time of appearance of the kidney after tracer injection, intensity of background, size and homogeneity of tracer uptake by the kidney. Although small, the pilot study could distinguish between hyperacute rejection, acute rejection, chronic rejection and cyclosporin toxicity.


Introduction
Attempts have previously been made to detect renal transplant pathology scintigraphic ally, usually with 99mm Tc DTPA. The most successful of these is probably the perfusion index.l" Others include functional imaging' and fractional mean transit time." With all these aids at hand, diagnosis of renal transplant pathology is still difficult. Serial scintigraphy of both perfusion and function often over a period of days or weeks is necessary for decent monitoring of the progress in renal transplants.
To aid the detection of pathology in renal transplants, a different approach to reading the scintigram was tested, based on renal and background information on the scintigram.
Renal perfusion, uptake and excretion using 99m Tc Glucoheptonate to page 17 The renal transplant scorea different vvav of evalu<'lting renal transplant pathology (rampage 16 was scored on selected criteria. The score was compared to the histological diagnosis of various transplants. Glucoheptonate was chosen for interpretation of function (perfusion and early excretion) and parenchymal integrity (delayed views after furosemide injection).

Method
Eight renal transplants were imaged using 99m Tc Glucoheptonate and biopsied within 24 hours of the scintigraphy for histological diagnosis.
150 MBq of 99m Tc Glucoheptonate were injected into an antecubital vein while a dynamic acquisition of 60 frames of one second was in progress, anterior to the patient. The camera field of view included the renal transplant, large blood vessels, spleen, ureter and bladder.
The first acquisition phase was immediately followed by a second phase of 120 frames of 15 seconds, imaging kidney function. A delayed static view of the transplant was acquired 3 hours later after 20 mg furosemide injection.
The perfusion frames were combined to 15 frames of 4 seconds and the 120 frames of function were combined to 15 frames of 2 minutes. A renogram was generated and frames were displayed, assessed and scored for perfusion, uptake and excretion.

Perfusion criteria (phase I) included:
Background score: o -Photopenic region in place of kidney 1 -Maximal kidney intensity equal to background 2 -Maximal kidney intensity between background and liver 3 + 2 + 2 + 2 + 3 = 12 Table I shows the perfusion scores for the various patients. Table II shows the function scores for the same group of patients. Perfusion and uptake of tracer in acute and hyper-acute transplant rejection are seen in Figures 1     and 2. Figure 3 shows the renogram and the half life of tracer in the blood from a region of interest over the heart  study.The perfusion score as estimated in our patient group showed a clear difference between the normal transplant, acute and chronic rejection. Attempts have been made previously to use sulphur colloid to predict transplant rejection. These were however unsuccessful."

Results
It has been shown previously that cyclosporin toxicity causes parenchymal tracer retention but does not impair perfusion." Such patient presented with a moderate perfusion but good function score in our study.
In hyper-acute rejection there was no perfusion or uptake of the tracer.
in a patient with acute rejection. Figure 4 is a bar diagram that compares perfusion and function scores (converted to percent) for various transplant pathologies.
Perfusion and function score of renal transplants with various pathologies. Our pilot study suggests that a renal transplant score may be a way to distinguish renal transplant pathology. Further evaluation of score criteria and exploration of the method with different tracers is necessary. Figure 3a: Renogram of a transplant undergoing acute rejection.

Discussion
Perfusion scintigraphy is a good indicator for acute rejection in renal transplants. This has often been