Extranodal Rosai-Dorfman Disease: A Rare Mimicker of Metastatic Renal Cell Carcinoma.

A 29-year-old female presented with the history of pain in the abdomen and a palpable lump in the right hypochondrium, lumbar, and the umbilical regions for the past 2 months. On evaluation with contrast-enhanced computed tomography (CECT) and positron emission tomography CT, she was found to have a heterogeneously enhancing mass entirely replacing the mid and the lower pole of the right kidney, the pelvis, and the upper ureter with loss of fat planes with the inferior vena cava, psoas muscle, and the hepatic flexure, along with pericardial deposits and soft tissue lesions at multiple paravertebral regions and the right thigh. Owing to a high suspicion of metastatic renal cell carcinoma (RCC), a right cytoreductive nephrectomy was performed. Histopathology revealed extranodal Rosai-Dorfman disease, which was mimicking a metastatic RCC on imaging. The patient was started on oral steroids to control the distant lesions and to prevent progression of the disease and is doing well at follow up.