CECT Features of Xanthogranulomatous Pyelonephritis (XGPN)
XGPN on CECT characteristically demonstrates multiple low-density fluid-filled cavities within an enlarged kidney with perinephric extension, typically associated with an obstructing renal calculus (most commonly staghorn) and hydronephrosis. 1
Primary Parenchymal Features
Renal enlargement is the most consistent finding, present in virtually all cases of XGPN on CECT. 2
Multiple dilated calyces with abnormal parenchyma appear in approximately 82% of cases, creating a characteristic multiloculated appearance. 2
Low-density fluid-filled areas within the renal parenchyma represent the hallmark CT feature, corresponding to dilated calyces filled with purulent material and lipid-laden macrophages. 1
Focal fat deposits within the inflamed renal parenchyma are identifiable in approximately 27% of cases, appearing as areas of negative attenuation values. 2
Associated Obstructive Features
Renal or upper ureteric calculus causing obstruction is present in 55-90% of cases, with staghorn calculi being particularly common. 3, 2
Hydronephrosis is demonstrable in all cases with solid tumors and represents a near-universal finding. 4
Non-functioning kidney on urography is one of the commonest findings when excretory studies are performed. 1
Extrarenal Extension Patterns
Perinephric extension occurs in 91-100% of cases and should be considered one of the most typical CT features of XGPN. 1, 2
Perinephric fat stranding and thickening of Gerota's fascia are present in all solid tumor cases. 4
Perinephric or psoas abscess develops in approximately 14-18% of cases. 3, 2
Extensive retroperitoneal inflammation extends beyond the perinephric space in approximately 27% of cases. 2
Diffuse vs. Focal Forms
Diffuse XGPN (88% of cases) involves the entire kidney with global enlargement and multiple cavities throughout. 3
Focal XGPN (12% of cases) presents as a localized mass, often mimicking renal cell carcinoma, and may be bifocal in rare instances (8.3%). 4, 3
Critical Diagnostic Pitfalls
The "great imitator" designation reflects XGPN's ability to mimic renal malignancy, particularly in focal forms where preoperative distinction from renal cancer is extremely difficult. 4
Cystic masses occur in 25% of cases, further complicating differentiation from cystic renal neoplasms. 4
Preoperative misdiagnosis is common, with pyonephrosis suspected in 50% of cases and neoplasia suspected in approximately 10% of cases. 3
Key Distinguishing Features
The combination of multiple low-density cavities, perinephric extension, obstructing calculus, and hydronephrosis should strongly suggest XGPN rather than malignancy. 1
Contrast-enhanced CT is the imaging modality of choice for diagnosing XGPN preoperatively, superior to ultrasound or unenhanced imaging. 1
The average tumor size in pseudotumoral presentations is approximately 6.6 cm. 4