Answer to Case 1-6
1. Axial (Fig1a ) and coronal MPR* (Fig1-b) images through the left kidney.
The left kidney is enlarged and contains multiple large, round, low attenuation
(−10–30 Hounsfi eld units) lesions, but maintains a normal shape. The low
attenuation lesions represent enlarged calyces, abscesses or granulomas. This is
sometimes called the bear paw sign. A few calculi are seen within the kidney (but
not obstructing the renal pelvis – obstructing calculi are seen in 75% of cases
with this condition). There is perinephric stranding and thickening of Gerota’s
fascia. Appearances are of Xanthogranulomatous pyelonephritis (XGP).
Figure.1c is a nephrectomy specimen with thickened and dilated upper
ureter and pelvis. Yellow deposits produce space occupying lesions throughout
the kidney and extend into adipose tissue adjacent to the upper pole.
Microscopically the yellow deposits are a xanthogranulamatous infl ammatory
reaction. This is a chronic infl ammatory process in which lipid-laden histiocytes
destroy the renal parenchyma with potential extension of an infl ammatory mass
into the perinephric space adjacent psoas muscle and posterior abdominal wall.
Squamous cell carcinoma is a rare complication.
When it extends outside the kidney, XGP may mimic tumour. No radiological
features are defi nitive of XGP, but the low density lesions in the presence of an
obstructive calculus, which is often a staghorn, are highly suggestive. Diagnosis
is made histologically by the presence of foamy lipid-rich macrophages accompanied
by acute- and chronic-phase infl ammatory cells.
2. Antibiotics and conservative therapy do not tend to be successful. Nephrectomy
is the treatment of choice, with the removal of all the granulomatous tissue to
prevent ongoing infl ammation leading to fi stula formation. Partial nephrectomy
may be appropriate if only a part of the kidney is involved.