CEUS for the diagnosis of acute graft pyelonephritis in renal transplant recipients

Acute graft pyelonephritis (AGPN) is a clinically relevant complication in renal transplant recipients, in whom diagnosis may be challenging because of nonspecific clinical and conventional ultrasound findings. Contrast-enhanced ultrasound (CEUS) enables real-time assessment of renal microvascular perfusion without nephrotoxic contrast agents. This study aimed to evaluate the diagnostic performance of CEUS for detecting AGPN in renal transplant recipients.

This retrospective single-center study included 66 consecutive renal transplant recipients who underwent CEUS for clinically suspected AGPN. The final clinical diagnosis, based on the integration of clinical, laboratory, microbiological, and available imaging findings, was used as the reference standard. Conventional ultrasound findings and CEUS parenchymal perfusion abnormalities were assessed. Diagnostic performance was evaluated in terms of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratios.

AGPN was confirmed in 21/66 patients (31.8%). Fever was more frequent in patients with AGPN than in those without AGPN (100% vs. 73.3%, p=0.014). On conventional ultrasound, globular graft appearance (14.3% vs. 0%, p=0.029), cortical hyperechogenicity (23.8% vs. 0%, p=0.002), cortical hypoechogenicity (28.6% vs. 4.4%, p=0.010), perirenal fluid collection (38.1% vs. 11.1%, p=0.018), and ureteral wall thickening (42.9% vs. 8.9%, p=0.002) were significantly associated with AGPN. CEUS correctly identified 19/21 AGPN cases, with two false-negative and no false-positive examinations. Sensitivity was 90.5% (95% CI 69.6-98.8%), specificity 100% (95% CI 92.1-100%), PPV 100% (95% CI 82.4-100%), and NPV 95.7% (95% CI 85.5-99.5%).

CEUS showed high diagnostic accuracy for AGPN in renal transplant recipients. By providing real-time assessment of graft parenchymal perfusion without nephrotoxicity or ionizing radiation, CEUS may represent a valuable complement to conventional ultrasound and potentially reduce the need for contrast-enhanced CT in selected patients. Larger prospective multicenter studies with standardized independent reference standards are warranted.