- sRCC can closely mimic XGP clinically and radiologically; a bear-paw appearance does not exclude renal cell carcinoma.
- Red flags for malignancy: culture negative infection, antibiotic-refractory fever within 7-10 days, progressive transfusion-requiring anaemia.
- CT findings specific for malignancy: irregular solid enhancing component and vascular invasion warrant prompt surgical exploration or tissue diagnosis.
Front Oncol. 2026 Jul 22;16:1798397. doi: 10.3389/fonc.2026.1798397. eCollection 2026.
ABSTRACT
BACKGROUND: Sarcomatoid renal cell carcinoma (sRCC) is a rare, highly aggressive malignancy that can closely mimic xanthogranulomatous pyelonephritis (XGP) on clinical, laboratory, and radiological grounds. While sRCC masquerading as XGP has been previously reported, existing literature lacks a structured analysis of the specific features that discriminate these entities and a practical framework for clinical decision-making.
CASE PRESENTATION: A 65-year-old female presented with a four-month history of anorexia and one week of postprandial abdominal distension. Contrast-enhanced CT demonstrated right renal enlargement with heterogeneous density, nephrolithiasis, and a bear-paw-like appearance, leading to an initial diagnosis of XGP. However, several features were inconsistent with typical XGP: persistently negative urine and blood cultures, an irregular solid component with heterogeneous arterial-phase enhancement, subtle renal vein irregularity suggestive of vascular invasion, progressive transfusion-requiring anemia, and persistent high fever despite 24 days of escalating broad-spectrum antibiotics (culminating in meropenem plus vancomycin). Repeat CT showed no radiological improvement. Right radical nephrectomy was performed on hospital day 31. Histopathology confirmed sRCC with lymphovascular invasion and a Ki-67 index of 50-55%. Despite initial recovery, the patient developed rapid multi-organ metastasis and succumbed to the disease.
CONCLUSION: When a presumed renal infection is culture-negative, antibiotic-refractory, associated with progressive anemia, and radiologically non-resolving, malignancy should be suspected early. The presence of an irregular solid enhancing component and vascular involvement on CT are malignancy-specific red flags that should not be overlooked. A bear-paw-like appearance does not exclude RCC. Short-interval failure of antibiotic therapy (7-10 days) should trigger surgical exploration or tissue diagnosis rather than prolonged empirical treatment.
PMID:42558360 | PMC:PMC13437527 | DOI:10.3389/fonc.2026.1798397
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