Cabral, P

Ferreira, S

Paixão, P

Penha, D

Rosado, E

Repositório do Hospital Prof. Doutor Fernando Fonseca

Page 1 of 14Xanthogranulomatous pyelonephritisPoster No.: C-0535Congress: ECR 2013Type: Educational ExhibitAuthors: E. Rosado, P. Cabral, D. Penha, P. Paixao, S. Ferreira; Amadora/PTKeywords: Inflammation, Diagnostic procedure, Ultrasound, CT, Kidney,AbdomenDOI: 10.1594/ecr2013/C-0535Any information contained in this pdf file is automatically generated from digital materialsubmitted to EPOS by third parties in the form of scientific presentations. Referencesto any names, marks, products, or services of third parties or hypertext links to third-party sites or information are provided solely as a convenience to you and do not inany way constitute or imply ECR's endorsement, sponsorship or recommendation of thethird party, information, product or service. ECR is not responsible for the content ofthese pages and does not make any representations regarding the content or accuracyof material in this file.As per copyright regulations, any unauthorised use of the material or parts thereof aswell as commercial reproduction or multiple distribution by any traditional or electronicallybased reproduction/publication method ist strictly prohibited.You agree to defend, indemnify, and hold ECR harmless from and against any and allclaims, damages, costs, and expenses, including attorneys' fees, arising from or relatedto your use of these pages.Please note: Links to movies, ppt slideshows and any other multimedia files are notavailable in the pdf version of presentations.www.myESR.orgPage 2 of 14Learning objectivesTo describe and illustrate imaging features of xanthogranulomatous pyelonephritis.BackgroundXanthogranulomatous pyelonephritis is an uncommon form of chronic pyelonephritis,characterized by destruction of renal parenchyma and replacement by lipid-laden foamymacrophages. It is believed to result from an atypical, incomplete immune response tosubacute bacterial infection. The most common organisms implicated are P. mirabilis andE. coli, but a variety of other bacteria may be found. Some cases occur in associationwith a renal pelvic calculus and obstruction is believed to be a contributing factor.Female patients are more frequently affected than male patients in a ratio of 2.1. Patientsare usually in mid-life and have a long history of recurrent urinary tract infection. Other riskfactors include diabetes and nephrolithiasis. Generalized symptoms include low-gradefever, malaise, chills, anorexia and weight-loss. Nonspecific urinary symptoms includeflank pain and haematuria.Although the diagnosis can often be suspected based on imaging studies, thedefinitive diagnosis requires histological examination. At microscopy, the calicealmucosa is ulcerated and replaced by necrotic debris with numerous inflammatory cells,particularly polymorphonuclear leucocytes. The medullary area is replaced by lipid-ladenmacrophages, admixed with lymphocytes and plasma cells. In the superficial corticalareas, there is fibrous replacement of the kidney with few nephrons remaining. Extensionof the xanthogranulomatous inflammation into the perinephric space is common.Treatment usually consists of extended open nephrectomy.Imaging findings OR Procedure detailsBefore the widespread of cross-sectional imaging, a pre-operative diagnosis ofxanthogranulomatous pyelonephritis was possible in only a small percentage of patients.The most characteristic radiographic finding is a large staghorn calculus. Additionalfindings include enlargement of the renal outline and, with more advanced disease,obscuration of the ipsilateral psoas margin. Excretory urography demonstrates apronounced decrease of the renal function of the affected side.Page 3 of 14US typically demonstrates an enlarged kidney with loss of normal renal architectureand a central echogenicity that corresponds to a staghorn calculus (Fig. 1). It isgenerally associated with acoustic shadowing. Dilated calices filled with pus mayappear as hypoechoic inhomogeneous areas in the renal sinus (Fig.2). In focalxanthogranulomatous pyelonephritis a focal inflammatory mass is seen. It is virtuallyimpossible to differentiate from a renal abscess or a necrotic renal cell carcinoma.CT is the mainstay of diagnostic imaging for xanthogranulomatous pyelonephritis as itallows a confident diagnosis and gives information about the extra-renal extent of thedisease.CT demonstrates an enlarged kidney with multiple hypodense edge shaped areasrepresenting dilated calices and pus filled cavities (Fig.3). Negative attenuation due tolipid rich xanthogranulomatous tissue may be also observed. The walls of these cavitiesusually show strong enhancement after contrast administration, denoting the markedvascularity of granulation tissue and compressed normal parenchyma (Fig.3). A centralobstructive calculus within a contracted or hydronephrotic renal pelvis is sometimesseen (Fig.4). The kidney is generally non-functioning with delayed or absent contrastexcretion. Extrarenal extension is characterized by stranding and inflammatory changesin the perinephric fat and associated thickening of the renal fascia (Fig.5). Spread beyondthe perinephric space may occur into the posterior and anterior pararenal spaces, psoasmuscle, diaphragm, chest and abdominal wall (Fig. 6). Fistula formation is a possiblecomplication.Atypical findings include massive pelvic dilatation, absence of stones (10%), renalatrophy (13%), and presence of gas in renal parenchyma. Although gas is rarely seen, itmay be confused with pyonephrosis or emphysematous pyelonephritis.Focal xanthogranulomatous pyelonephritis is seen in approximately 10% of patients.Some of these cases are related to a duplicated collecting system and demonstratefindings similar to those seen in the diffuse form. Others closely mimic the features of abacterial abscess or a neoplasm (Fig. 7). In this case, the diagnostic is almost alwaysmade after nephrectomy.Diffuse xanthogranulomatous pyelonephritis can be staged based on CT findingsaccording to the degree of extrarenal involvement. Stage 1 includes the cases withinvolvement limited to the kidney (Fig. 8). In stage 2 inflammatory changes extend to theperirenal fat within the renal fascia (Fig. 9). In stage 3 involvement extends beyond therenal fascia into the retroperitoneum, thorax, peritoneal cavity or abdominal wall tissues(Fig 10).MRI is also a valuable tool for diagnosing xanthogranulomatous pyelonephritis, asit is extremely sensitive for identifying the accumulation of the lipid-laden foamymacrophages as high-intensity signal on T1-weighted images. Chemical shift and short-tau inversion recovery imaging usually increase the sensitivity of fat detection. However,Page 4 of 14angiomyolipoma, renal cell carcinoma and retroperitoneal sarcoma occasionally containfat tissue, and therefore those entities may be extremely difficult to differentiate fromxanthogranulomatous pyelonephritis.Images for this section:Fig. 1: Renal utrassound of a female patient with xanthogranulomatous pyelonephritis.The image demonstrates a staghorn calculus occuping most of the renal sinus andproducing posterior acustic shadowing.Page 5 of 14Fig. 2: Renal US of a 65 year-old woman with xanthogranulomatous pyelonephritis.The image demonstrates an enlarged left kidney (18cm in major axis) with multiplehypoechoic round areas corresponding to the pus filled dilated calicies.Page 6 of 14Fig. 3: Contrast enhanced abdominal CT of a female patient with xanthogranulomatouspyelonephritis. The kidney is enlarged and have multiple hypodense edge shaped areaswith hyperenhancing walls.Page 7 of 14Fig. 4: Volume rendering reconstruction of an abdominal CT demonstrates the three-dimensional appearance of a staghorn calculus.Page 8 of 14Fig. 5: Contrast enhanced abdominal CT of a female patient with xanthogranulomatouspyelonephritis. The kidney contains multiple hypodense cavities and a central obstructingcalculus. The renal facia is thickened and hyperenhancing. Pronounced stranding andinflammation of the perirenal fat.Page 9 of 14Fig. 6: Abdominal CT of a 59 year-old woman with xanthogranulomatous pyelonephritisand extra-renal extension. The affected kidney is enlarged with multiple hypodenseareas. The inflammation spread beyond the perirenal space into the abdominal wall,forming an abscess.Page 10 of 14Fig. 7: Focal xanthogranulomatous pyelonephritis in a 61 year-old woman. Contrastenhanced abdominal CT demonstrates a large heterogeneous masse in the lower poleof the left kidney. It contains some focus of calcification and air. Imaging methods cannotdistinguish this lesion from a renal abscess or a neoplasm. Histological examinationproved a focal xanthogranulomatous pyelonephritis.Page 11 of 14Fig. 8: Staging of xanthogranulomatous pyelonephritis according to the degree ofextrarenal involvement. In stage 1 inflammation is limited to the kidney.Page 12 of 14Fig. 9: Staging of xanthogranulomatous pyelonephritis according to the degree ofextrarenal involvement. In stage 2 inflammatory changes extend into the perinephricspace.Page 13 of 14Fig. 10: Staging of xanthogranulomatous pyelonephritis according to the degree ofextrarenal involvement. In stage 3 inflammation extends beyond the renal fascia involvingadjacent tissues as the lateral abdominal wall shown in the image.Page 14 of 14ConclusionXanthogranulomatous pyelonephritis is a chronic granulomatous process induced byrecurrent bacterial urinary tract infection. Although US is useful in the diagnosis of thiscondition, CT is the main imaging tool, providing specific findings of nephromegaly,renal function impairment, urinary obstruction due to calculi and multiple hypodenseedge shaped areas. Extra-renal extent is common. In a few atypical cases thepreoperative diagnosis cannot be made by CT. The definitive diagnosis requireshistological examination.References1. Kim JC. US and CT findings of xanthogranulomatous pyelonephritis. ClinImaging. 2001;25(2):118-212. Dunnick NR, Sandler CM, Amis ES, Newhouse JH. Renal inflammatorydisease. In: Dunnick NR, Sandler CM, Amis ES, Newhouse JH, editors.Textbook of uroradiology. 2nd ed. Baltimore: Williams & Wilkins, 1997. pp.163- 89.3. Loffroy, R. Guiu, B. Watfa, J. Michel, F. Cercueil, J.P. Krause D.Xanthogranulomatous pyelonephritis in adults: clinical and radiologicalfindings in diffuse and focal forms. Clin Radiol. 2007 Sep;62(9):884-904. Craig WD, Wagner BJ, Travis MD. Pyelonephritis: radiologic-pathologicreview. Radiographics. 2008 Jan-Feb;28(1):255-775. Anezinis P, Prassopoulos P,Daskalopoulos G, Mavromanolakis E,Gourtsoyiannis N, Cranidis A. MRI and CT features in two unusual cases ofxanthogranulomatous pyelonephritis. Eur J Radiol. 1998 Aug;28(1):98-101.Personal Information

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Repositório do Hospital Prof. Doutor Fernando Fonseca