Pyramidal appearance and resistive index: insensitive and nonspecific sonographic indicators of renal transplant rejection.

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Abstract
Renal transplantation patients undergoing biopsy were examined with duplex Doppler sonography to establish the sensitivity and specificity of this technique in the detection of rejection. The study population consisted of 89 consecutive patients, who received renal transplants 1 week to 17 years before our examination and underwent 96 core needle biopsies within 24 hr of sonography. The resistive index (RI), defined as the difference between the peak systolic and end diastolic flow velocities divided by the peak systolic velocity (expressed as a percentage), was measured in the main, segmental, interlobar, and arcuate renal arteries. Furthermore, the prominence of the renal pyramids, as determined by their size and echogenicity, was prospectively evaluated. Biopsy was used to establish diagnosis, but in cases of equivocal results, hospital course was the final arbiter. The most frequent diagnoses in the patients were acute rejection (41 patients) and chronic rejection (19 patients). Receiver-operating-characteristic curve analysis established that, regardless of the vessel in which it was measured, the use of RI to assign a diagnosis of acute rejection was no better than establishing this in a random manner. We did note, however, that patients with chronic rejection or cyclosporine toxicity were unlikely to have RIs greater than 80%. We further found that prominent pyramids were neither sensitive nor specific in the detection of acute rejection and that prominent pyramids were not correlated with elevated RI.