The patient, a 46-year-old male, was admitted to the hospital on November 17, 2004 because of “recurrent abdominal pain, diarrhea and purulent blood stool for more than 10 months after resection and radiotherapy for a malignant mesenchymal tumor of the sacrococcygeal region. On December 28, 2003, the patient underwent a cold abdominal exploration for “sacrococcygeal tumor” in an outside hospital. The tumor was then resected. The postoperative pathology indicated “spindle cell tumor with active cell growth, dense cell arrangement and moderate anisotropy in some areas, which was consistent with malignant mesenchymal tumor when combined with tumor size and immunohistochemical results.” On January 25, 2000, he was treated with pelvic radiation therapy (total dose of 400 Gy in 15 doses), and on January 30, 2004, he developed abdominal pain, diarrhea, pus and blood stools, and a feeling of urgency. After admission to our hospital, he had lost 3 kg of weight, and the CT examination of the abdomen showed “pelvic sacrococcygeal tumor; circumferential thickening of the rectal wall, and radiological enteritis was considered clinically. The e-colonoscopy suggested “6~14cm from the anus, the mucous membrane was obviously congested and edematous, and the intestinal lumen was narrowed; about 40cm from the anus, the mucous membrane was obviously congested and edematous, and the intestinal lumen was narrowed, and the endoscope could not pass.” The results of barium enema examination suggested “stenosis of the upper rectum and the junction of the sigmoid colon and descending colon; the pre-sacral space of the rectum was significantly widened.” Diagnosis: (1) Residual mesenchymal tumor of the sacrococcygeal region. (2), Radiation sigmoid and proctitis. (3), Sacrococcygeal mesenchymal tumor after partial resection. Drug enema (saline 250 ml plus hydrocortisone 0.1g plus stannous 3.0g plus lidocaine 0.lg plus metronidazole 0.5g, reserved enema 2 times/d) was given. After 7d of fasting and total parenteral nutrition support, a percutaneous endoscopic gastrostomy was performed, and parenteral nutrition was gradually reduced, and enteral nutrition through gastrostomy was gradually increased, and transitioned to total enteral nutrition support after 2d. Until December 14, 2004, the patient was discharged from the hospital and continued to receive home total enteral nutrition support, while insisting on drug enema. During this period, the abdominal pain, diarrhea, urgency and pus and blood stool symptoms were improved. On February 17, 2005, the patient was hospitalized again due to incomplete intestinal obstruction and could not tolerate enteral nutritional support, and his weight increased by about 1 kg compared with the previous hospitalization. The patient was firstly placed in a lithotomy position, and the left lower abdomen was entered through the rectus abdominis incision, and the descending colon, sigmoid colon and rectal wall, rectal mesentery and peritoneum were found to be pale and thickened, with a thick and hard texture, showing changes of chronic radiation enteritis. There was a hard mass of about 4 cm in diameter in the pelvic floor, which was closely attached to the sacrococcygeal bone, and the rectal lumen was narrowed and hard in front of the mass. The lesioned sigmoid colon and rectum were excised, and the distal rectum was closed with continuous sutures. The upper edge of the tight adhesion formed by the tumor and the sacrococcygeal bone was sharply separated. Since the lower edge of the tumor was too deep to be separated, the patient was changed to a prone folding position, and the lower end of the sacrococcygeal tumor was separated by removing the coccyx through a median sacrococcygeal approach, and the tumor was completely removed. The patient was changed to a lying position again, and the descending colonic stump was dragged out of the stoma in the left lower abdomen. Postoperative pathological examination: (1), pelvic spindle cell tumor with vitreous degeneration or necrosis involving the sacrum, consistent with post-radiotherapy changes of isolated fibrous tumor. (2), Chronic ulceration of colon and rectum with mild heterogeneous hyperplasia of some intestinal epithelium and ganglion cell hyperplasia, consistent with radiological colorectal changes. Postoperatively, the patient recovered well. The stoma began to pass stool at 5 d after surgery, and the transition from intravenous nutrition to enteral nutrition was made. The gastrostomy tube was removed 17 d after surgery, and the patient was discharged after fully resuming a transoral diet. Despite the great progress in radiotherapy equipment and technology, it is estimated that about 5% of patients still suffer from rectal and sigmoid radiation damage after pelvic radiotherapy, which can seriously impair bowel function and even lead to death. The reason for this is that the sigmoid colon and rectum are relatively fixed and easily exposed to excessive irradiation, and the higher the irradiation dose, the higher the risk of radiation injury. The treatment of this patient has gone through two stages: non-surgical and surgical treatment. Non-surgical treatment can temporarily relieve the symptoms and improve the patient’s general condition, which can also provide a favorable opportunity for future surgery. Nutritional support plays a pivotal role in the non-operative treatment. For those who cannot tolerate enteral nutrition or the part of enteral nutrition is not enough, it can be supplemented by intravenous nutrition. The following difficulties exist in the surgical treatment of this case: (l), the timing of surgery: chronic radiation enteritis should be operated as early as possible, but most radiation enteritis complicated by intestinal obstruction is not an emergency, and patients should receive adequate supportive treatment and preoperative preparation. If possible, surgery should be delayed until the body obtains positive nitrogen balance after nutritional support. (2) Treatment of the diseased intestinal canal: For patients who need surgical treatment due to complications of chronic radiation enteritis, the diseased intestinal canal should be removed during the first operation. The ideal condition for intestinal anastomosis is that the intestinal canal at both ends of the anastomosis is free of disease. Occlusive endarteritis and interstitial fibrosis caused by radiation injury make the intestinal canal vulnerable to damage and have poor healing ability. The risk of fistula will be increased when the descending colon and distal rectal anastomosis are performed. The risk of fistula increases with the resection of the diseased sigmoid colon and upper rectum and the closure of the distal rectum, and a descending colostomy is an ideal option. It should be emphasized that the stoma site should be located outside the irradiated field of the intestine. (3) Treatment of sacrococcygeal tumor: The patient’s sacrococcygeal tumor is located in the anterior sacral space (posterior rectal space), with deep location and complex surrounding anatomy. In addition, after pelvic surgery and pelvic radiotherapy, the pelvic tissues are closely adhered. Therefore, using abdominal incision and combined with sacrococcygeal incision to remove the sacrococcygeal tumor is a reasonable operation. The complete removal of the residual tumor in the sacrococcygeal region achieved the effect of radical treatment. If tumor recurrence and chronic radiological damage to the distal rectum are ruled out in the future follow-up, the patient will have the opportunity to operate again to return the stoma and restore the intestinal continuity.