Magnetic resonance urography of renal papillary necrosis

Sir, Renal papillary necrosis is a well-described entity on intravenous pyelogram (IVP) and CT urogram in both the adult and pediatric populations [1–3]. However pediatric renal papillary necrosis is less frequently encountered, particularly on magnetic resonance urogram [4–6]. Indeed, to the best of our knowledge renal papillary necrosis has yet to be described on MR urogram. We present a case of renal papillary necrosis demonstrated by MR urogram in a child with previously undiagnosed sickle cell trait. A 17-year-old previously healthy African-American girl presented to our institution with a 3-day history of gross hematuria. Her medical history was unremarkable except for recent streptococcal pharyngitis. After 2 months of extensive and inconclusive evaluation, including laboratory analysis, renal US, and a renal biopsy, the hematuria persisted, with hemoglobin decreasing to 4 g/deciliter. The girl was subsequently evaluated by cystoscopy, which demonstrated hemorrhage from the left ureteral orifice. Retrograde pyelogram and cystoureteroscope showed irregularity of the left upper pole papillary urothelium (Fig. 1). At this point, the pediatric urologist was suspicious but not confident of the diagnosis of renal papillary necrosis. Symptoms persisted, so MR urography was performed. MR urogram demonstrated classic changes of bilateral papillary necrosis (Fig. 2). Given these findings, a hemoglobin electrophoresis led to the diagnosis of sickle cell trait. The girl was placed on aminocaproic acid with cessation of hematuria. Imaging of renal papillary necrosis, which is most commonly caused by sickle cell disease and nonsteroidal anti-inflammatory medications in the pediatric population, is well documented within the radiology literature, with Praetorius first describing its radiologic appearance in 1937 [2]. Classically, intravenous pyelogram has been the examination of choice. From its appearance on intravenous pyelogram, multiple classic radiographic signs have been elucidated, e.g., ballon-tee, lobster claw, and signet ring. Recently several authors have demonstrated the imaging appearance and diagnosis of renal papillary necrosis in adults using CT urography [3]. However, given the use of iodinated contrast agent and the radiation dose of both CT and intravenous pyelogram, alternative imaging modalities are helpful for pediatric imaging in suspected renal papillary necrosis. In 1995 Rothpearl et al. [6] reported the techniques and application of MR urography in the depiction of the kidney and bladder pathology. One patient included in this study population had pathologically proven renal papillary necrosis. However, the authors did not elucidate whether the changes of renal papillary necrosis were demonstrable on MR urogram [6]. In a subsequent invited commentary, Hattery and King [7] called into question the utility of MR urogram in the detection of papillary necrosis given the resolution requirements for depicting the subtle changes of renal papillary necrosis at the caliceal and forniceal levels [7]. The authors did J. Schroeder Medical University of South Carolina, College of Medicine, Charleston, SC, USA