Primary follicular lymphoma in the renal pelvis: A rare case report.

BACKGROUND Follicular lymphoma (FL) is more common in lymph nodes, while primary extranodal lymphomas are rare. Urinary tract lymphoid neoplasms are extremely rare, accounting for less than 5% of all extranodal lymphomas. Only one case of FL from the renal pelvis has previously been reported. CASE SUMMARY A 70-year-old male patient with a history of esophageal cancer visited our hospital for follow-up examination. Abdominal computed tomography revealed a malignant mass in the right renal pelvis. The whole-body positron emission tomography/computed tomography showed a significant increase in fluorodeoxyglucose uptake of this soft tissue mass and no abnormal fluorodeoxyglucose uptake in the esophageal wall. The patient underwent radical resection of a malignant tumor in the right kidney, which was confirmed by postoperative pathology to be FL. The patient received no radiation or chemotherapy after surgery, and no recurrence of lymphoma or other malignant tumors was found at the 1-year follow-up. CONCLUSION Extranodal FL is more common in the skin and gastrointestinal tract but rarely occurs in the urinary tract. This is the second report of primary renal FL. Localized extranodal FL is expected to have a favorable prognosis and can be cured by local resection.