Focal xanthogranulomatous pyelonephritis mimicking a renal tumor: CT- and MR-findings and evolution under therapy. K. Ramboer, R. Oyen, S. Verellen2, ...
Nephrol Dial Transplant ( 1997) 12: 1028–1030
Nephrology Dialysis Transplantation
Case Report
Focal xanthogranulomatous pyelonephritis mimicking a renal tumor: CT- and MR-findings and evolution under therapy K. Ramboer, R. Oyen, S. Verellen2, S. Vermeersch2, A. L. Baert and R. Verberckmoes1 Departments of Radiology and 1Nephrology, Catholic University of Leuven, Departments of 2Radiology and 3Urology, Medical Center NO-Limburg, Maaseik, Belgium
Key words: xanthogranulomatous pyelonephritis; MR; kidney disease; CT; kidney, inflammatory disease; pseudotumors; ultrasonography
Introduction Xanthogranulomatous pyelonephritis is a rare but grave chronic renal infection of unknown pathogenesis with female predominance. The term ‘xanthogranulomatous’ refers to the infiltration of the renal parenchyma with large lipid-laden macrophages, known as xanthoma cells [1 ]. Pyuria and bacteriuria are frequently but not uniformly present. Proteus mirabilis is the most common causative agent; other bacteria may be found occasionally. The disease is usually unilateral but rare cases of bilateral involvement have been reported [2,3]. Xanthogranulomatous pyelonephritis is frequently associated with nephrolithiasis or obstructive uropathy. Yet, xanthogranulomatous pyelonephritis may occur without clear predisposing uropathy. Based on the morphological aspect, two main types are distinguished. In the most common form the kidney is diusely aected with diminution of function. Irreversible parenchymal destruction requiring nephrectomy may ensue [2,4]. The rare focal form may be dicult to dierentiate from a renal cell carcinoma. This dierentiation though is important because nephrectomy may be avoided by appropriate treatment.
inflammatory process, the urinary sediment was normal, cultures of blood an urine didn’t grow microorganisms. A chest X-ray was normal. Abdominal ultrasonography revealed a hypoechoic solid mass in the right kidney (Figure 1 ) and with low resistance flow on Doppler-examination. On plain CT the mass was slightly hyperdense compared to the renal parenchyma, with small areas of low density at the periphery. There was mild and heterogeneous enhancement after intravenous injection of iodinated contrast medium (Figure 2 a,b). The hypoattenuating areas at the periphery of the lesion were located well within the confines of a thick capsule or pseudocapsule. The perirenal fat showed some strands and Gerota’s fascia was thickened ( Figure 2b). No calculi were detected and no signs of urinary obstruction nor of duplication of the urinary tract were present. No enlarged lymph nodes were seen. On fast T2-weighted MR-images (HASTE-sequence) the mass was slightly hyperintense (Figure 3a), while on T1-weighted images and fat suppressed sequences the mass was hypointense (Figure 3b ). A striking feature was the triangular shape
Case report A 29-year-old woman was referred for investigation of recurrent episodes of fever since 5 months, signs of general illness and a weight loss of 6 kg. She complained of headache, nausea, and right sided low lumbar pain. Micturation was normal. Serum creatinine was normal, blood tests revealed signs of an Correspondence and oprint requests to: Prof. Dr R. Oyen, Department of Radiology, University Hospitals, Catholic University of Leuven, Herestraat 49, B-3000 Leuven, Belgium
Fig. 1. Ultrasonography of the right kidney: Hypoechogenic mass lesion in the lower part of the right kidney protruding into the sinus.
© 1997 European Renal Association–European Dialysis and Transplant Association
Focal xanthogranulomatous pyelonephritis
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Fig. 2. Contrast enhanced CT showing two contiguous slices of a rounded slightly heterogeneous and hypoattenuating mass in the lower pole (4.3 cm). (a) Hypoattenuating areas are recognized at the periphery of the mass well within the confines of a thick wall. (b ) There is only mild infiltration of the perinephric fat.
Fig. 3. MRI performed 4 days after the CT scan: mass lesion with triangular shape and displaying heterogeneous signal intensities on HASTE sequences (a). The mass is homogeneous isointense compared to the surrounding parenchyma on the fat-suppressed images with selective water excitation ( b).
of the parenchymal defect, the base directed to the surface of the kidney and the top bulging in the renal sinus. The diagnosis of focal xanthogranulomatous pyelonephritis was suspected, although a tumoral process could not be excluded with certainty. An empirical treatment with ofloxacine was started and continued for 8 weeks. During treatment the fever subsided and the serum parameters of inflammation showed improvement already after a few days. After 5 weeks of treatment a follow-up CT scan showed an almost total disappearance of the mass ( Figure 4). Another 6 weeks later, the CT scan was completely normal.
Discussion Focal xanthogranulomatous pyelonephritis may be erroneously interpreted as renal cell carcinoma or Wilms tumor. The heterogeneous and solid aspect on CT is indeed often indistinguishable from hypovascular renal cell carcinoma. Especially when, as in this case,
Fig. 4. Contrast enhanced CT 6 weeks after the initial scan: normal appearance of the renal parenchyma in the lower pole of the right kidney.
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no signs of renal obstruction, lithiasis nor of urinary infection are present, the diagnosis may be equivocal [3,5–9 ]. Lithiasis or urinary obstruction may be present in up to 80% of cases. Features that have been considered to be characteristic though not pathognomonic for xanthogranulomatous pyelonephritis include the renal enlargement, strands in the perinephric fat, thickening of Gerota’s fascia, and thick enhancing septa separating hypodense areas in the renal parenchyma [1,2,5,8,10]. The hypodense areas in the periphery of the renal mass are likely to be explained by xanthoma cells or by incorporation of perinephric fat [2,10,11]. Previous reports of MRI in xanthogranulomatous pyelonephritis are limited, but both CT and MRI are equally suited to display the morphology of this uncommon renal disease [7,12]. In this particular patient the diagnosis of focal xanthogranulomatous pyelonephritis was suggested because of the wedgeshaped aspect on CT and because of the absence of hyperintensity on fast T2-weighted sequences [13]. Needle aspiration biopsy could have been helpful for the diagnosis. However, because xanthogranulomatous pyelonephritis may occur simultaneously with a transitional cell carcinoma or renal cell carcinoma, the idea was rejected. Thus, although a tumor could not be excluded with certainty, we decided to try an empirical treatment with close follow-up. The diagnosis of focal xanthogranulomatous pyelonephritis in this case was based on clinical and radiological data and the follow up under antibiotic therapy. Complete healing of histologically proven xanthogranulomatous pyelonephritis without discernible renal scarring has been reported previously [6,14].
Teaching point Focal xanthogranulomatous pyelonephritis may be hard to dierentiate from renal parenchymal tumors. No single clinical or radiological sign is pathognomonic. However MRI and especially the fast
K. Ramboer et al.
T2-weighted sequences (HASTE), thus enabling to exclude a tumoral mass, may be useful in the dierentiation. The diagnosis is important because nephrectomy can be avoided and renal recovery by appropriate antibiotic treatment may be complete.
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