FRCR MCQ----Xanthogranulomatous pyelonephritis

                    MCQ ON Xanthogranulomatous pyelonephritis 

Q. All are  true regarding Xanthogranulomatous pyelonephritis except:
a.renal pelvic stones in approx 70%
b.multiple rounded high  attenuation areas(65 to 80HU)
c.large size
d.usually associted with proteus infection

ANS: b---multiple rounded low-attenuation areas (-15 to -20HU) noted on CT due to foamy histiocytes

• Xanthogranulomatous pyelonephritis is an uncommon form of chronic parenchymal inflammation in which an excess of foamy histiocytes gives a yellowish appearance to the cut surface of the kidney. 
• It is usually associated with a Proteus infection in patients with calculus disease. 
• The condition is seen in two forms: focal and generalized.
• The generalized form of the disease is more common. 
• It may be suspected on the urogram if, in the presence of infection and calculi, the pelvicalyceal system fails to fill where there is a good thickness of renal substance. 
• Computed tomography shows multiple rounded low-attenuation areas (-15 to -20HU), representing dilated debris-filled calyces and xanthoma collections. 
• The kidney is large but retains its reniform shape.
•  Perinephric inflammatory change is seen in 90% of cases. 
• Approximately 70% show renal pelvic stones. 

REF:

Adam: Grainger & Allison's Diagnostic Radiology, 5th ed.