A case of IgG4-related mesenteritis.

IgG4-related disease is a newly recognized fibroinflammatory condition characterized by tumefaction consisting of fibrosis with dense infiltration of IgG4-positive plasma cells; affecting various organs. A case of IgG4-related sclerosing mesenteritis is reported. A 64-year-old man was admitted to our hospital with a suspected tumor of the small intestine. Abdominal computed tomography demonstrated a 6-cm soft tissue mass in the right lower mesentery compressing the jejunum, which also showed accumulation of fluorodeoxyglucose uptake on fluorine-18 fluorodeoxyglucose positron emission tomography. With a preoperative diagnosis of suspected malignant lymphoma with lymphadenopathy in the mesentery, partial small bowel resection was performed. Macroscopically, a hard mass, including several swollen lymph nodes, was detected in the mesentery. Microscopically, marked fibrosis showing partially storiform pattern, obstructive phlebitis, follicular hyperplasia, and abundant infiltration of IgG4-positive plasma cells were detected. IgG4-related mesenteritis was diagnosed histopathologically, but the serum IgG4 level was 81 mg/dl postoperatively. Five months after the surgery, an 11-cm soft tissue mass involving the left ureter appeared. Histological examination of a biopsy specimen from the retroperitoneal mass showed fibrosis with inflammatory infiltration. Although IgG4-related retroperitoneal fibrosis could not be confirmed histologically, the tumor responded well to steroid therapy.