You are in: eMedicine Specialties > Radiology > GENITOURINARY Xanthogranulomatous PyelonephritisArticle Last Updated: May 13, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia Ali Nawaz Khan is a member of the following medical societies: American Institute of Ultrasound in Medicine, Radiological Society of North America, Royal College of Physicians, Royal College of Physicians and Surgeons of the United States, Royal College of Radiologists, and Royal College of Surgeons of England Coauthor(s): Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Colm Boylan, MRCP, FRCR, Specialist Registrar, Department of Radiology, North Manchester General Hospital NHS Trust, UK; Brendan Costello, MD, Clinical Director, Department of Urology, North Manchester General Hospital; Khalid Mahmood, MBBS, FCPS, Locum Appointment Training Specialist Registrar, Department of Radiology - Paediatric, Royal Liverpool (Alder Hey) Children's Hospital Editors: John L Haddad, MD, Clinical Associate Professor, Department of Radiology, Weill Medical College of Cornell University; Director of Body MRI, Department of Radiology, Methodist Hospital in Houston; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Joshua A Becker, MD, Professor, Department of Radiology, New York University School of Medicine; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Clinical Assistant Professor of Radiology, University of Washington Medical School Author and Editor Disclosure Synonyms and related keywords: suppurative granulomatous reaction, XGPN, focal xanthogranulomatous pyelonephritis, diffuse xanthogranulomatous pyelonephritis, global xanthogranulomatous pyelonephritis, flank pain, xanthoma cells, pyuria, dysuria, hematuria, proteinuria, microscopic hematuria, urinary tract infection, UTI, inflammatory kidney, chronic pyelonephritis, staghorn calculi, avascular renal mass, renal cell carcinoma, RCC, cystic renal carcinoma, renal tuberculosis, renal xanthomas INTRODUCTIONSection 2 of 12
  BackgroundXanthogranulomatous pyelonephritis (XGPN) represents an unusual suppurative granulomatous reaction to chronic infection, often in the presence of chronic obstruction from a calculus, stricture, or tumor. XGPN is characterized histologically by the presence of foamy, lipid-containing macrophages (xanthoma cells), diffuse infiltration with plasma cells, and histiocytes. XGPN is more common in women than in men; female patients with XGPN usually have a history of recurrent or chronic urinary tract infections.1, 2, 3, 4 Presenting symptoms may include pyuria, flank pain, fever, dysuria, pyuria, hematuria, proteinuria, or microscopic hematuria.2, 5 A palpable flank mass may be present, which may be tender or demonstrate costovertebral angle tenderness. XGPN is rare in children.3 Two forms of XGPN are described, a diffuse or global form (83-90% of patients) and a focal form (10-17%). XGPN has been termed the great imitator because it may be misdiagnosed as a renal neoplasm, especially if the lesion is focal. Typically, plain abdominal radiographs demonstrate a large renal calculus (staghorn in 75% of patients), whereas intravenous urograms demonstrate an enlarged, poorly opacified kidney that is associated with a centrally obstructing calculus. Ultrasonographic findings of diffuse disease depict an enlarged kidney that usually preserves the reniform shape. Multiple hypoechoic areas may exist; these represent hydrocalyces, small abscesses, or granulomas. The obstructing calculus may not create shadowing. The treatment of patients with XGPN usually involves intensive antimicrobial therapy, but surgery is invariably required to completely eradicate the infection and the accompanying calculus and/or obstruction. Kidney-sparing surgery may be undertaken in patients with focal disease. For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education articles Urinary Tract Infections, Kidney Stones, and Blood in the Urine. PathophysiologyXGPN almost always occurs unilaterally, and to the author's knowledge, only 1 patient with bilateral disease has been described. The kidney is involved either globally or focally. Changes of XGPN have been described in kidneys destroyed as a result of pyonephrosis; in renal cell carcinoma; in transitional cell carcinoma; and, rarely, in a renal cyst. These focal pathologic changes are detectable only by using histologic analysis, and they usually do not appear on images. XGPN has been described in 3 stages, as follows:
On gross examination, the focal form of the disease is usually seen as a renal mass. On cut sections, the mass appears as a yellowish-white, solid or semisolid structure that is indistinguishable from renal cell carcinoma. In global disease, the kidney is enlarged, and indurated or thickened perinephric fat is associated with it. The renal pelvis is dilatated and often contains staghorn calculi. Soft, yellow nodules replace the corticomedullary junction, and the calyces are filled with pus and debris. Microscopically, both the focal and global forms appear similar, with diffuse infiltration by plasma cells, histiocytes, and lipid-laden foam cells.3 The foam cells contain neutral fat and cholesterol (ester granules) that test positive for periodic acid-Schiff (PAS) stain. PAS staining is useful in differentiating these cells from the clear cells found in renal cell carcinoma. Laboratory testing frequently shows an elevated erythrocyte sedimentation rate (ESR), leukocytosis, elevated gamma-globulin levels, and anemia. Proteinuria and pyuria are frequent. Urine cultures may reveal Proteus mirabilis, Escherichia coli, Staphylococcus aureus, and Klebsiella, Pseudomonas, and Enterobacter species.1, 4, 6 Urine cultures may show negative results in 30-39% of patients despite positive results from the kidneys. Occasionally, different organisms may be isolated from the urine and from the removed kidney, underscoring problems with antimicrobial therapy. Abnormal results in liver function tests are found in as many as 50% of patients, and these are occasionally associated with hepatomegaly. The cause of the liver abnormalities is not known, but results of liver function tests return to normal after treatment. Inflammation resulting from XGPN may extend into the perirenal space, pararenal space, ipsilateral psoas muscle, colon, spleen, diaphragm, posterior abdominal wall, and skin. FrequencyUnited StatesXGPN is found in 1-18% of patients in whom the kidneys require nephrectomy because of inflammatory conditions. SexThe female-to-male incidence is 3-4:1. AgePatients typically present at the age of 45-65 years, but individuals of all ages may be affected, including infants. Clinical DetailsThe typical patient is a middle-aged, obese, diabetic female with a staghorn calculus, recurrent fever, dysuria, and flank pain that are unresponsive to antibiotics. Other symptoms include dysuria, pyuria, hematuria, proteinuria, or microscopic hematuria. A palpable flank mass may be present, which may be tender, or the patient may exhibit costovertebral angle tenderness. XGPN is rare in children. Frequently, urinary symptoms, fever, and flank pain are absent, and minimal, if any, leukocytosis is found; therefore, excluding renal cell carcinoma is difficult on clinical grounds alone. Abnormal results in liver function tests are reversible in as many as 50% of patients and are occasionally associated with hepatomegaly. Patients (40%) are often symptomatic for 6 months before XGPN is diagnosed; however, the reported duration of symptoms before presentation is extremely variable, ranging from 3 days to 8 years. Urinalysis results demonstrate pyuria, proteinuria, and microscopic hematuria. Urine cultures demonstrate infection by P mirabilis, E coli, S aureus, and Klebsiella, Pseudomonas, and Enterobacter spp. Preoperative differentiation of XGPN and chronic pyelonephritis on the basis of clinical, bacteriologic, and radiologic criteria is problematic.7 Patients with XGPN are more likely to be middle-aged women with diabetes mellitus, with frequent history urinary tract infections in both pathologies. Both conditions present with flank pain and tenderness. Anemia, hematuria, and bacteriuria are more frequent in XGPN patients than in those with chronic pyelonephritis. In one study, P mirabilis was detected in over 50% patients with XGPN and in a minority of the chronic pyelonephritis group.7 Nephromegaly and renal calculi are more frequently seen in both pathologies. XGPN has a higher rate of postoperative complications. Preferred Examination
Related eMedicine topics: Limitations of TechniquesNo radiologic features are characteristic for XGPN, but in the diffuse form, some CT scan and ultrasonographic features may be sufficiently typical to suggest a preoperative diagnosis in the appropriate clinical setting.7 Focal disease cannot be diagnosed with confidence radiologically and should be regarded as malignant until proven otherwise. The importance of urine cultures in assessing an unexplained renal mass cannot be overemphasized. DIFFERENTIALSSection 3 of 12
Other Problems to Be ConsideredAvascular tumor (on angiography) RADIOGRAPHSection 4 of 12
Findings
Degree of ConfidenceAlthough plain radiographs may suggest a renal calculus and a soft-tissue mass, and although an intravenous urogram may suggest no renal function on the affected side, the findings of neither method can confirm the diagnosis of XGPN. False Positives/NegativesDifferentiating acute pyelonephritis, other chronic renal infections (eg, tuberculosis), straightforward renal calculus disease, and renal neoplasms from XGPN on plain radiographs and intravenous urograms is not always possible. CT SCANSection 5 of 12
FindingsCT scanning is the most useful investigation for the preoperative assessment of XGPN.1, 5, 9, 10, 11 CT scan findings depend on the morphologic type of XGPN.
Degree of ConfidenceNone of the features described above are characteristic of XGPN, but they are sufficiently typical of the diffuse form of XGPN to suggest a preoperative diagnosis in the appropriate clinical setting, especially by low CT scan values. Focal disease cannot be diagnosed with confidence with radiologic images, and the lesions should be regarded as malignant until proven otherwise. The importance of urine cultures in assessing an unexplained renal mass cannot be overemphasized. False Positives/NegativesUncomplicated renal calculus disease, acute pyelonephritis with renal abscess formation and perinephric spread, chronic renal infections (eg, renal tuberculosis), and renal neoplasms cannot always be differentiated confidently from XGPN on the basis of CT findings alone. MRISection 6 of 12
FindingsA few reports describing the MRI appearances of XGPN have been published.5, 11, 12, 13, 14 Documented findings include the presence of a large mass in the renal fossa that appears multiloculated. Abscesses and calyces demonstrate intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images. Calcification and renal calculi appear as signal voids. MRI appears to be extremely sensitive in outlining perinephric spread.11 Residual parenchyma in the unaffected kidney may appear normal. Degree of ConfidenceMRI findings have been inconsistent, with varying degrees of signal change described in areas involved by the inflammatory process compared with normal uninvolved renal tissue. In general, CT scan findings appear to be more helpful than those obtained with other modalities. False Positives/NegativesSimilar to CT scan results, MRI features are not reliable in differentiating XGPN from complicated and uncomplicated renal calculus disease, acute pyelonephritis with perinephric spread, and renal neoplasms. ULTRASOUNDSection 7 of 12
Findings
Degree of ConfidenceAlthough ultrasonographic features are not specific to XGPN, the failure to depict a normal kidney associated with a staghorn calculus suggests the diagnosis. Ultrasonographic results are not routinely helpful in identifying renal calculi, and ultrasonography is less sensitive than other modalities in demonstrating extrarenal spread. False Positives/NegativesThe ultrasonographic appearance of XGPN may be mimicked by a simple hydronephrosis associated with a calculus, pyonephrosis, renal tuberculosis, renal cystic neoplasm, and renal lymphoma. In simple hydronephrosis, the dilatated calyces are sharply defined and demonstrate enhanced through-transmission. Pyonephrosis often demonstrates fluid-debris levels. NUCLEAR MEDICINESection 8 of 12
FindingsRadionuclide studies usually do not contribute to the diagnosis, but isotope renography is extremely useful in assessing differential renal function when surgery is contemplated. The authors have demonstrated renal uptake of technetium 99m (99mTc)-labeled white cells in XGPN (unpublished data). ANGIOGRAPHYSection 9 of 12
FindingsThe features of angiography described in the global disease include stretching of the segmental and/or interlobular arteries around large avascular masses, similar to those seen in hydronephrosis. Attenuation occurs in major renal arteries, and peripheral vessels lack arborization. Inhomogeneity of the nephrogram may mimic hydronephrosis. In the late arterial phase, hypervascularity or arterial blush may be noted around the periphery of the masses due to granulation tissue. The focal form of XGPN is usually hypovascular. Intrarenal veins are stretched and compressed by inflammatory renal masses. The renal vein may be encased or occluded, but inferior vena cava thrombosis has not been described. Degree of ConfidenceAngiography no longer plays a diagnostic role in XGPN, although the authors occasionally use angiography to characterize focal renal masses or to plan surgery. The invasive catheter technique is being replaced with CTA and MRA with reformatting images False Positives/NegativesThe angiographic appearance of XGPN may mimic those of hydronephrosis or avascular renal neoplasms. INTERVENTIONSection 10 of 12
Needle biopsy may be helpful in differentiating XGPN from other renal masses. Percutaneous nephrostomy may be necessary to treat patients who present with acute septicemia due to an obstructive form of the disease associated with pyonephrosis. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
Xanthogranulomatous Pyelonephritis excerpt Article Last Updated: May 13, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
