小腸間膜に発生した炎症性筋線維芽細胞性腫瘍の1例

Inflammatory Myofibroblastic Tumor Arising From the Mesentery of the Small Intestine, Report of a Case

要旨　67歳，男性患者が約2年前，右腎癌に対しての手術中に，偶然腹腔内腫瘤を発見された．小腸粘膜もしくは腸間膜原発かは不明であったが，肉眼的に肉腫を否定することができず小腸切除術が行われた．小腸腸管壁から漿膜側へ管外性に発育する白色調充実性の粘膜下腫瘤を3個認めた．割面ではいくつかの分葉状結節が形成されていた．いずれの腫瘍においても腸間膜脂肪織内を主体として，線維芽細胞が種々の程度の膠原線維とやや浮腫状の間質を背景に，形質細胞，リンパ球，好酸球を主体とする炎症細胞浸潤を伴って境界不明瞭に増生し，一部小腸の固有筋層から粘膜に浸潤していた．腫瘤内部には血管の増生が目立っていた．免疫組織化学染色ではvimentinのみが陽性であったが，肉眼像，組織像から炎症性筋線維芽細胞性腫瘍として矛盾しないと考えられた．炎症性筋線維芽細胞性腫瘍はまれに腸管膜に発生し，gastrointestinal stromal tumorや腸間膜デスモイドとの鑑別が必要となる．

　During on operation for right renal carcinoma 2 years ago, a 67-year-old man was found by chance to have intraabdominal masses. Small intestinal resection was performed because it was unclear whether the masses originated from the mucosa or mesentery of the small intestine and it could not be definitely denied that, macroscopically, the mass were mesenteric sarcoma. There were three submucosal tumors, solid and whitish colored, protruding into the serosa side continuously from the intestinal wall. On the cut surface, some lobulated nodules were noted. The tumors composed of fibroblastic cell proliferation were mainly located in the adipose tissue of the mesentery with a variable degree of collagen fibers, slightly edematous stroma, and inflammatory cells that included plasma cells, lymphocytes, and eosinophils. Blood vessels were conspicuous throughout the tumor. At the periphery, the tumor was not clearly demarcated and the tumor cells focally infiltrated into the mucosa and muscularis propria of the small intestine. Immunohistochemically, the tumor cells were positive for vimentin. The characteristic macro and microscopic findings led us to a diagnosis of inflammatory myofibroblastic tumor (IMT). IMT sometimes arises from the mesentery of the small intestine and it is necessary to differentiate it from gastrointestinal stromal tumor and mesenteric desmoid.

　1) Division of Clinical Laboratory, National Cancer Center Hospital, Tokyo

　2) Division of Pathology, National Cancer Center Research Institute, Tokyo