IgG4-related disease is diagnosed when both the elevation of the serum IgG4 level and invasion of IgG4-positive interstitial cells and sclerosis to a tumor are noted. Some cases have demonstrated malignant disease. In the head and neck lesion in particular, IgG4-producing mucosa-associated lymphoid tissue (MALT) lymphoma has arisen during the treatment of IgG4-related disease. We herein report the first case of IgG4-producing MALT lymphoma during the treatment of IgG4-related disease in the renal hilum. A 79-year-old man was being followed for autoimmune pancreatitis and IgG4-related sclerosing cholangitis. During follow-up, magnetic resonance cholangiopancreatography detected a mass in the renal hilum, so he was referred to our department for a further examination. Positron emission tomography-computed tomography detected a standard uptake of 9.7, and the tumor size was gradually increasing. Due to these findings, laparoscopic nephro-ureterectomy was performed. A pathological examination revealed IgG4-producing marginal zone B cell lymphoma. We herein report a rare case of IgG4-producing B cell lymphoma in the renal hilum.
