Inflammatory myofibroblastic tumor (IMT) is an uncommon mesenchymal solid tumor commonly documented in children and young adults [1,2]. Although it occurs primarily in the lung, IMTs in many organs including stomach, small intestine, large intestine, liver, mediastinum, retroperitoneum and bladder have also been documented [1,2]. The clinical presentation is determined by the site of origin and the effects of the mass. Thus, IMT presents with non-specific clinical symptoms and its diagnosis can be difficult. IMT derived from the gastrointestinal (GI) tract presents with clinical symptoms of anemia, GI obstruction, fecal occult blood positive or intussusception. Those are not specific symptoms in IMT because other GI tract tumor may also present with similar symptoms [1,3,4]. IMT has been synonymously referred to as inflammatory pseudotumor, pseudosarcomatous myofibroblastic lesion, pseudosarcomatous fibromyxoid lesion or plasma cell granuloma. These words are synonymous and have been in common use, all sharing a key pathologic differentiation; a dominant spindle cell proliferation with a variable inflammatory component. These spindle cells are in fact myofibroblasts, thus, the preferred term for reference should be IMT reflective of the pathologic characters despite the persistence of others [5].

A 35-year-old man presented with anal bleeding after defecation for 2 weeks. It is not associated with the symptoms of abdominal pain, fever or weight loss. He had taken oil mixed with a trace of benzopyrene for 3 years because of his job of checking oil type in the edible oil plant. He had been treated for variant angina and underwent herniorrhaphy for inguinal hernia 12 years ago. Vital signs, physical examination, and peripheral blood analysis (hemoglobin 14.5 g/dL, hematocrit 43.2%) were in the normal range. Colonoscopy demonstrated a 4.0 cm sized-mass with shallow ulceration in the central area and irregular margin accompanied by intact mucosa (Fig. 1). Microscopic examination of biopsy specimens showed chronic inflammation. Computer tomography showed a well-demarcated and homogenous solitary mass in the descending colon. On contrast enhanced view, the mass had enhanced homogeneously in delayed phase (Fig. 2A, B). Colonoscopy was performed for clipping and tattooing and the patient underwent a laparoscopic anterior resection. On laparoscopy, a considerable amount of ascites (about 30 mL) and enlarged mesocolic lymph nodes were shown. The lymph nodes were resected and frozen biopsy concluded all lymph nodes were negative for malignancy. Because the main tumor was found to arise from descending colon, left colic branch of inferior mesenteric artery (IMA) and inferior mesenteric vein were ligated while IMA was preserved, then laparoscopic anterior resection was performed. After the main mass was resected, hand-sewing colocolic anastomosis was performed. The 3.9 × 3.8 cm sized mass grossly presented a fungating surface, white to yellow color and invaded muscularis propria (Fig. 3). Consistency of the mass was harder than adenocarcinoma. The histopathologic examination of the specimens showed the tumor was composed of a proliferation of spindle-shaped cells arranged in hyaline material with chronic inflammatory cells, composed mainly of plasma cells and lymphocytes, not neutrophils. The specimens did not have celluar atypia or hyperchromatism in the cells (Fig. 4A, B). Immunohistochemical staining suggested that fibroblastic tissue was of myofibroblastic nature. Immunohistochemically, tumor cells were positive for smooth muscle actin, and vimentin, and negative for desmin, CD117 (c-kit), anaplastic lymphoma kinase (ALK)-1 (Fig. 5A, B).

IMT was originally described in the lungs in 1937, and since then has been reported at various sites such as mesentery, stomach, small intestine, large intestine, liver, mediastinum, retroperitoneum and bladder [1,2,6]. The most common site of IMTs is the lung and the most common sites of extrapulmonary inflammatory myofibroblastic tumor are the mesentery and omentum [1,2,6,7]. Among extrapulmonary IMT, 43% arose in the mesentery and omentum [7]. Although it occurs primarily in children and young adults (mean age, approximately 10 years), in more recent years a broad age range has been documented [1]. There is no difference in incidence between females and males, though each report has a difference in mean age and gender ratio [2,5].