Post-nephrectomy foreign-body granuloma in the retroperitoneum mimicking lymph node metastasis of renal cell cancer

Recently, iatrogenic foreign-body granuloma has been increasingly reported. The asymptomatic presentation and confusing appearance of granuloma can lead to misdiagnosis of a secondary malignancy, especially for a patient with a corresponding past medical history. Sometimes, surgical treatment is unavoidable, and the diagnosis relies upon the pathologic result. Herein, we report an unusual case of a 43-year-old man who underwent a nephrectomy for renal cell carcinoma (clear cell type) 5 years ago. A secondary granuloma was identified behind the inferior vena cava in the retroperitoneum 6 months after the surgery, but the radiologists had failed to identify it throughout the 4 years of routine examination. Later on, the lesion was identified by positron emission tomography, which classified it as a highly 18F-fluorodeoxyglucose-avid lesion. Considering no visible foreign-bodies identified on images, the lesion was arguably diagnosed as a lymph node metastasis of renal cancer. Finally, it was confirmed as a foreign-body granuloma encasing surgical suture and adipose tissue by the pathological analysis.