US and CT findings of xanthogranulomatous pyelonephritis

Jong Chul Kim*

Department of Diagnostic Radiology, Chungnam National University Hospital, 640 Daesa-dong, Jung-gu, Taejon, 301-721, South Korea

Received 10 October 2000

Abstract

Ultrasonographic and computed tomographic findings of 21 cases of pathologically proven xanthogranulomatous pyelonephritis (XGP) in

20 patients were retrospectively evaluated. Seventeen (81%) were diffuse, and extrarenal extension occurred in 13 cases (62%). The kidney

was enlarged diffusely in 12 cases (57%), and focally in 3 (14%). Urinary calculi were present in 16 cases (76%), with staghorn calculi in 4 of

these, and hydronephrosis occurred in 17 (81%). In addition to typical features of XGP, the condition may also show variable imaging

findings. D 2001 Elsevier Science Inc. All rights reserved.

Keywords: Kidney, US; Kidney, CT; Kidney, inflammation; Kidney, diseases

1. Introduction

Xanthogranulomatous pyelonephritis (XGP) is a well

recognized but rare type of chronic pyelonephritis classi-

cally occurring in middle-aged women [1,2]. The disease

has been reported at all ages and in both sexes [3–9]. If

imaging findings show typical features of XGP such as

nephromegaly, renal function impairment, and urinary

obstruction due to calculi, the diagnosis of XGP may

be easy. However, if XGP shows atypical imaging find-

ings, the diagnosis or differential diagnosis of XGP may

be difficult. Even though cases of XGP have been

reported from all parts of the world, either as isolated

case reports or as small series of patients, it is difficult to

find radiologic reports analyzing large series of XGP

patients [5].

This study was performed to determine ultrasono-

graphic (US) and computed tomographic (CT) findings

of XGP through the retrograde image analysis of patho-

logically proven 20 XGP patients.

2. Materials and methods

Twenty-one cases of pathologically proven XGP in 20

patients (bilateral in one patient) who received nephrectomy

during the past 13 years were included in this study.

US was performed using a 3.5- or 5-MHz probe of SL-2

(Siemens Medical Systems, Erlangen, Germany), a 3.5-

MHz probe of Diansonic DRF 400 (Diasonic, Milpitas,

CA, USA), a 3.5- or 5-MHz probe of Aloka SSD 630,

650, 280 (Aloka, Tokyo, Japan), a 3.5-MHz probe of

Acuson 128 (Acuson, Mountainview, CA, USA), a 4–7-

MHz convex probe of Ultramark 9 HDI or 2–4 MHz curved

probe of 3000 HDI (Advanced Technology Laboratories,

Bothell, WA, USA). CT images were obtained using GE

8800, High Speed Advantage or Cti standard (General

Electric Medical Systems, Milwaukee, WI, USA), or Soma-

tom Plus VD 30 (Siemens Medical Systems), with and

without intravenous bolus injection of Ultravist 300 (Iopro-

mide 0.6234 g/ml, 140–150 cm3, Korea Schering, Ansung,

Korea). Both US and CT were performed in 19 patients, and

in one patient only US was obtained. Slice thickness and

slice interval on CT were 5–10 mm.

The findings of US and CT were retrospectively eval-

uated with regard to distribution and extent of the disease,

kidney size, the presence of calculi, hydronephrosis, and

renal function. The radiologic findings were evaluated by

three urologic radiologists who reached a consensus on their

interpretations. Imaging and pathologic findings in each

0899-7071/01/$ – see front matter D 2001 Elsevier Science Inc. All rights reserved.

PII: S0899 -7071 (01 )00262 -5

* Corresponding author. Tel.: +82-42-220-7835; fax: +82-42-253-

0061.

E-mail address: jckim@cnuh.co.kr (J.C. Kim).

Journal of Clinical Imaging 25 (2001) 118–121

patient were compared. The demographic and clinical find-

ings of 20 patients were also evaluated.

3. Results

Sixteen of the 20 patients with XGP were female, and 19

patients except a 3-year-old boy were adults. The age of the

patients ranged from 3 to 61 years (mean = 45).

The chief complaints of 20 patients on admission were

recurrent fever (n = 6), dysuria (n = 7), flank pain (n = 3), and

suspected renal mass (n = 4). Clinical findings of inflamma-

tion such as fever, pyuria, bacteriuria, or leucocytosis were

noted in all patients.

US and CT findings of 20 patients were correlated well

with their postoperative pathologic findings. In all patients

except a 50-year-old man (Fig. 1), the disease was unilateral

(Figs. 2 and 3). The disease site of the 19 patients with

ipsilateral XGP was the right kidney in 13 of the patients

and the left kidney in 6.

In one patient, XGP was bilateral, and there were thus 21

cases. Seventeen (81%) of these were diffuse (Fig. 2), while

Fig. 1. A 50-year-old man with bilateral focal XGP. Precontrast (A) and

postcontrast (B) CT scans show functioning kidneys with a large wedge-

shaped, less-enhancing nephrographic defect in the right kidney (small

arrows in B) and an ovoid hypodense abscess with thick wall in the left

kidney (arrowheads). Note the extension of this inflammatory process to the

perirenal space with thickening of Gerota’s fascia (larger arrows).

Fig. 2. A 3-year-old boy with diffuse XGP. (A) Coronal scan of right renal

US shows severe hydronephrosis due to an impacted renal pelvic stone with

acoustic shadowing (black arrow). The dilated calices contain abundant

debris. (B,C) Precontrast (B) and postcontrast (C) CT scans show dilated

pus-filled calices in the enlarged right kidney with a bullet-like pelvic stone

(black arrows). Note the parenchymal thinning, perirenal strands (black

arrowheads), thickening of Gerota’s fascia (thick white arrows), and no

excretion of contrast material from functionally impaired right kidney to the

right ureter.

J.C. Kim / Journal of Clinical Imaging 25 (2001) 118–121 119

four (19%) were focal (Figs. 1 and 3); extrarenal extension

(Figs. 1 and 2) occurred in 13 cases (62%), among which

ipsilateral pleural effusion was noted in two. The kidney

was enlarged diffusely in 12 of the cases (57%), and focally

in three (14%); urinary calculi (Fig. 2) were present in 16

(76%), with staghorn calculi in four of these; and hydro-

nephrosis (Fig. 2) occurred in 17 (81%). Impairment of

ipsilateral renal function was noted in 13 cases (62%).

4. Discussion

XGP is a rare form of chronic granulomatous inflamma-

tion characterized by destruction of the renal parenchyma

[1–9]. The disease is reported at all ages, but predominantly

affects patients, more often females, in the fifth through the

sixth decades of life [9]. In our study, 16 of the 20 patients

with XGP were female, and 19 patients except a 3-year-old

boy were adults, with the mean age of the patients being 45.

Bilateral XGP has been known to be rare [2,10,11], and our

study included one case of bilateral disease.

The classically described radiologic findings include a

staghorn calculus, absent or diminished excretion of contrast

medium on urography, and a poorly defined mass in the

enlarged kidney [12]. In our study, renal calculi were present

in 16 cases (76%), with staghorn calculi in four of these;

poor excretion of contrast medium on CT was found in 13

cases (62%); and nephromegaly occurred in 15 cases (71%).

There are two forms of XGP [2,12]. The diffuse or global

form (85%) is more common than the localized, focal, or

segmental form (15%). Diffuse XGP may be staged as

follows: Stage I, involvement is limited to the kidney; Stage

II, involvement extends to the renal pelvis or the perirenal

fat within Gerota’s fascia; Stage III, involvement extends

beyond Gerota’s fascia into the retroperitoneum, other

organs, or both [12]. In our study, 17 (81%) of 21 cases

were diffuse forms, with Stage I in four, Stage II in nine, and

Stage III in four of these. Renoalimentary, nephrocutaneous

or nephrobronchial fistula also may rarely be associated in

XGP patients [10,13–16]. The localized form of XGP is

sometimes referred to as ‘‘tumefactive’’ or ‘‘pseudotu-

moral’’ form of XGP, because the findings are easily

confused with a renal tumor such as renal cell carcinoma

in adults or a Wilms tumor in children [9,12,17,18]. Besides,

the differential diagnosis of XGP from hydro- or pyoneph-

rosis, malakoplakia, renal abscess, or lymphoma is some-

times difficult [9]. In our study, XGP was confused with a

renal cell carcinoma in one case, a Wilms tumor in another

case, with pyonephrosis in two cases, and with renal abscess

in another two cases.

Accurate diagnosis of XGP is usually not achieved

preoperatively, since presenting symptoms are not specific

and pathognomonic laboratory tests are not available [19].

Diffuse renal enlargement with a central echogenic focus

representing staghorn calculus is a classic US finding of

XGP. Acoustic shadowing from the renal calculi is, how-

ever, not always present; this has been attributed to the

presence of a dense peripelvic fibrosis [12] as in two cases

of our series. CT is considered an adequate method of

imaging evaluation of patients with clinically suspected

XGP [9,19]. The typical CT appearance of the more

common diffuse form of XGP is that of an enlarged kidney

with multiple hypodense egg-shaped areas arranged as in

hydronephrosis in coexistence with renal calculi [1,20,21].

Negative attenuation areas due to lipid-rich xanthogranu-

lomatous tissue, as well as calcifications within the mass,

may also be observed [19]. Diffuse XGP in an atrophic

kidney may, however, present nonspecific features. In

addition, localized XGP could be presented as a pseudotu-

moral cystic lesion, suggesting that XGP in such cases

Fig. 3. A 60-year-old man with focal XGP. (A) Precontrast CT scan

shows an iso- or slightly hypodense ovoid exophytic mass with

hyperdense rim in the anterolateral aspect of the right kidney (large

arrowhead) and an ill-defined slightly hypodense area in the medial

portion of the right kidney (arrow). The hyperdense rim in the former

lesion was pathologically proven to be due to thin calcifications. (B)

Postcontrast CT scan reveals irregular enhancement of the ovoid

exophytic mass with some internal nonenhancing foci (large arrowhead)

and the nonenhancing hypodense lesion in the medial portion of the right

kidney (arrow). Note some additional striate nephrographic defects

between these two lesions (small arrowheads). Due to the renal contour

bulging around the exophytic mass, renal cell carcinoma could not be

ruled out preoperatively, however, the mass was surgicopathologically

confirmed as focal XGP localized within the renal capsule.

J.C. Kim / Journal of Clinical Imaging 25 (2001) 118–121120

might be useful for the surgeon to plan an organ-sparing

procedure [9,22].

In conclusion, US and CT findings of XGP may show

not only the typical feature of nephromegaly, renal function

impairment, and urinary obstruction due to calculi, but also

variable imaging findings. If the images obtained in the case

of a middle-aged woman with clinical findings of urinary

infection show atypical findings, we believe that XGP

should be included in the differential diagnosis.

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