Magnetic Resonance Imaging as a Diagnostic Test for Renal Cell Carcinoma in Renal Transplant Patients with Acquired Polycystic Kidney Disease

Abstract

Introduction: Malignancy is a common cause of death in renal transplant recipients. Renal cell carcinoma is 15-fold increased in patients after kidney transplantation compared to the general population. Acquired cystic kidney disease (ACKD), defined as at least 3-5 cysts in one or both native kidneys, is one of the known risk factors. The Bosniak classification of renal cysts describes their morphological appearance on the basis of contrast enhanced computed tomography. This study was designed to establish magnetic resonance imaging (MRI) without contrast media as a diagnostic test to classify renal cysts and identify or exclude small tumors in renal transplant recipients that can not be exposed to contrast media. Methods: Renal ultrasound was used to screen renal transplant recipients for ACKD. Twenty-eight consecutive patients with ACKD received magnetic resonance imaging (MRI) of the kidneys. The imaging protocol consisted of a high resolution T2-weighted turbo spin-echo sequence with and without fat suppression (SPIR), an axial and coronal T1-weighted gradient echo sequence without contrast and an axial diffusion weighted sequence. All MRI studies were performed using a 1.5T system (Philips, Archiva, Best, The Netherlands). The mean size of the kidneys and the number of cysts in each kidney were measured. Based on the signal intensity on T1- and T2-weighted images all cysts were classified with a classification system adapted from the Bosniak classification. Results: We screened 214 renal transplant recipients for the incidence of ACKD using renal ultrasound. 25% of these patients had ACKD. Age (57.6±12.3 vs. 52.9±14.5 years) or time since development of end stage renal disease (13.5±6.6 vs. 13.3±7.6 years) were not different in patients with or without ACKD. In addition, the number of immunosuppressive drugs used (2.5±0.5 vs. 2.5±0.6) or the use of mTOR inhibitors (26% in patients with ACKD vs. 19% in patients without) was similar in patients with or without ACKD. Renal ultrasound did not allow a detailed Bosniak classification in most cases because of the multitude of cysts and the decreased echogenicity of the kidneys. Two patients had suspicious cystic kidney tumors identified by ultrasound. The first 28 consecutive ACKD patients received MRI. Renal MRI scanning revealed small kidneys (mean size 7.3 cm) with typically more than 10 cysts in each kidney and allowed a Bosniak classification in every case. Eleven patients (39%) had benign cysts of Bosniak stages I and II, 8 patients (29%) had Bosniak IIF cysts, while 7 patients (25%) had cysts fulfilling the criteria of Bosniak stage III. Two kidneys had Bosniak IV cystic lesions that were later confirmed histologically as renal cell carcinoma. Conclusion: Suspicious cystic lesions are common (54%) in renal transplant recipients with ACKD based on renal MRI test. Renal MRI without contrast media is a more sensitive and specific diagnostic test compared to renal ultrasound in separating patients with benign cystic lesions from patients with lesions suspicious for malignancy.