Inflammatory renal pseudotumor mimicking renal cell carcinoma with complete radiologic resolution: A case report

Small renal masses are increasingly detected incidentally, but up to 25% prove to be benign. Imaging alone often cannot distinguish malignant tumors from inflammatory or ischemic lesions, posing a risk of overtreatment. This case highlights a renal mass initially concerning for malignancy that resolved entirely following treatment for acute pyelonephritis A 51-year-old woman presented with bilateral flank pain, fever, and myalgias. Laboratory findings were consistent with a urinary tract infection, and cultures grew Escherichia coli. Imaging revealed a 4.4 cm right renal mass with features concerning for renal cell carcinoma. However, biopsy demonstrated arterionephrosclerosis without malignancy. Follow-up MRI at 3 months showed complete resolution of the lesion, suggesting a transient inflammatory pseudotumor related to acute pyelonephritis and chronic ischemia. This case illustrates the diagnostic overlap between renal cell carcinoma and benign renal lesions such as focal pyelonephritis, arterionephrosclerosis, or inflammatory pseudotumors. Despite radiologic features mimicking malignancy, clinical context and histology supported a non-neoplastic process. Renal mass biopsy, when combined with follow-up imaging, proved essential to avoid unnecessary intervention. Awareness of inflammatory mimics and their clinical course is critical in managing indeterminate renal lesions, particularly in patients with risk factors for infection or vascular disease. This case underscores the importance of integrating clinical, radiologic, and histologic data in evaluating renal masses. Biopsy and imaging surveillance can help differentiate benign mimics from malignancy, minimizing overtreatment and preserving renal function.