A Case of Reactive Lymphoid Hyperplasia That Is Difficult to Differentiate From Renal Cancer With Lymph Node Metastasis

Introduction: Reactive lymphoid hyperplasia (RLH) is a rare benign lymphoproliferative disorder that rarely involves the kidney and has not been reported in association with regional lymphadenopathy. Case Presentation: A 70-year-old woman was incidentally found to have a left renal mass. Contrast-enhanced computed tomography revealed a 20-mm enhancing renal lesion with enlarged hilar lymph nodes, leading to a preoperative diagnosis of renal cell carcinoma with nodal metastasis (cT1aN1M0). Open radical nephrectomy with regional lymphadenectomy was performed. Histopathological analyses established a diagnosis of reactive lymphoid hyperplasia. No additional treatment was administered, and the patient has remained free of recurrence for 3 months. Conclusion: We report the first case of RLH accompanied by regional lymph node enlargement. Because RLH can closely mimic renal cell carcinoma on imaging, it should be considered in the differential diagnosis of renal masses when the clinical presentation is inconsistent with typical renal cell carcinoma.