Inflammatory pseudotumor of the Kidney

BACKGROUND: Inflammatory pseudotumor of the kidney or inflammatory myofibroblastic tumor (IMT) is composed of spindle cells admixed with variable amount of proliferating myofibroblasts, fibroblasts, extracellular collagen, lymphocytes and plasma cells. This mainly affects the urinary bladder or prostate. Renal involvement is rare. CASE PRESENTATION: A 56 year-old man was diagnosed with asymptomatic left sided hydronephrosis while being investigated for rheumatoid arthritis. CT scan imaging showed ill defined fascial plains around the kidney and thickening around the renal hilum suggestive of localized inflammatory change. Worsening intermittent left loin pain with increasing hydronephrosis, significant cortical thinning and marked deterioration of renal function necessitated nephrectomy. Macroscopy showed a hydronephrotic fibrotic kidney with microscopy and immunohistochemistry consistent with a histological diagnosis of IMT. CONCLUSION: We report a case of an inflammatory pseudotumor of the kidney. It is unique in that the patient presented with painless hydronephrosis followed two years later with progressive deterioration in renal function and worsening loin pain.