Differential diagnosis, investigations, and treatment
The primary lesion was not identified on various examinations, but the lesion resolved spontaneously after approximately 6 months of follow-up. In February 2023, the patient was referred to our hospital for progressive anemia. A circumferential type 2 tumor was found at the anastomosis after resection of the ascending colon by colonoscopy, which was not found in July 2022 (Figure 2). The circumferential type 2 tumor was located at the ascending colon, and a biopsy revealed a malignant spindle tumor and the patient was referred to our department. Blood tests showed no elevation of tumor markers, and other tests were normal. Computed tomography revealed irregular wall thickening of 25 mm in the ascending colon and a 37-mm tumor in the mesentery of the small intestine, but no other obvious lesions (Figure 3). Magnetic resonance imaging showed a pale high signal on T2-weighted and diffusion-weighted images and a high signal on fat-suppressed T1-weighted images, suggesting mucus accumulation (Figure 4).
The patient was diagnosed with a malignant spindle cell tumor localized at the anastomosis. In March 2023, the patient underwent an open right hemicolectomy of the colon and limited lymph node dissection (because the lymph nodes had already been dissected in the previous surgery). Only one small nodule was found intraoperatively in the abdominal cavity. The nodule was submitted for pathological examination and diagnosed as scar tissue. The operative time was 252 min, with a blood loss of 120 mL. The patient was discharged on day 8 without any postoperative complications. Macroscopically, the anastomosis around the ascending colon, which was the primary site, revealed a circumferential 84×52 mm type 3 tumor with superficial necrotic tissue. The necrotic tissue adhered to the superficial layer (Figure 5A). Histologically, the tumor was greyish-white, dense, and situated in the intrinsic muscularis propria, with atypical spindle-shaped cells in the tumor area, infiltrating the subplasma membrane and showing atypical nuclear fission (Figure 5B). The colon serosa was filled with fibrous hyperplasia, vessel hyperplasia, inflammatory cell infiltration, and necrotic tissues. Further immunohistochemical analysis showed that the tumor cells positively stained for α1-antichymotrypsin (Figure 5C) and vimentin (Figure 5D), were S-100- and HMB-45-negative, and were MDM2-/CDK4-positive. Thus, the possibility of dedifferentiated liposarcoma could not be denied, and the pathological examination revealed an undifferentiated SCS centered on the anastomosis.