A 1-year-old boy was admitted to our hospital for "abdominal distension for 1 week and anus blockage, and no flatulence and defecation for 3 days". One week prior to being admitted, the child developed abdominal distension without obvious inducement, no fever, no nausea and vomiting, no diarrhea, and he received no special treatment. His symptom of abdominal distension persisted, and there was no flatulence or defecation for 3 days ago. So the child was admitted to our emergency department. Manifestations of the child at admission: shock; low blood pressure (55/30 mmHg); rapid heart rate (200 beats/min); significantly prolonged capillary refilling time (4 s); elevated lactic acid (3.4 mmol/L); lack of consciousness; dyspnea; severe abdominal distension. Indirect intra-abdominal pressure was 15 mmHg at this time. Arterial blood gas analysis showed metabolic acidosis and low levels of sodium and potassium. A blood routine test showed leukocytosis and mild anemia. Biochemistry showed a significant decrease in albumin. Conservative fluid resuscitation, ventilator support, and anti-infective therapy were used to maintain a stable internal environment. The General Pediatric Surgery Department was promptly consulted on the diagnosis and treatment of this child while we actively corrected his shock status as his abdominal distension was very severe.
Poor response; rhonchi in both lungs when breathing; no evident rales; distended and soft abdomen; no palpable abnormal mass. Anal examination: smooth finger entry; a mass (about 6 * 5 cm in size, poorly circumscribed, poor mobility) was palpable in the sacrococcygeal area; no blood staining after finger stall withdrawal. Body temperature 38.2  C, heart rate 200 beats/min, respiratory rate 50 breaths/min, blood pressure 55/30 mg.
Auxiliary examination: blood routine and biochemistry are shown in Table 1; tuberculosis antibody (-); fecal routine: occult blood (+), fecal culture (-); negative PPD test results (PPD is an intradermal test to diagnose tuberculobacter infection by injecting a small amount of tuberculin into the skin at the injection site.). Erect abdominal radiograph (Figure 1) indicated the intestine was pneumatic, dilated, rigid, and stiff, with a tendency to straighten, spaces between the intestine walls were thickened, and gas distribution was uneven. Intestinal obstruction was likely based on the erect abdominal radiograph. Abdominal B-mode ultrasound imaging: No evident causes of acute abdominal disease were detected, abundant gas accumulated in partial intestine, effusion was dilated in partial intestine, a hypoechoic area, about 5.1 * 4.9 * 4.8 cm in size was observed in the sacrococcygeal area, with a uniform echo, clear boundary, and regular shape. Color Doppler flow imaging (CDFI): punctate blood flow signal was observed, PSV: 25.6 cm/s, RI: 0.6. Whole blood was collected from the child before surgery. Serological tests revealed positive perinuclear antineutrophil antibody (P-ANCA) and elevated vasoactive intestinal peptide concentrations, both of which are markers that are currently highly distinctive in determining ulcerative colitis. 
Prompt exploratory laparotomy and decompression were performed as the abdominal pressure of the child continued to rise to the ACS level (abdominal compartment syndrome). It was found that small intestinal blood circulation was good, and the entire colon was dilated with a diameter of more than 6.1 cm and there was no blood circulation disturbance. TM was determined to be likely based on the above data and the patient's significant clinical manifestations of septic shock. Colonoscopy (Figure 2) revealed numerous purulent masses and ulcers on the surface of the colon. The pathology after colon biopsy (Figure 3) showed that the crypt structure had changed, and crypt abscess had formed. Mucosal and muscular layer eosinophils < 5 / HP, and ganglion cells can be seen in the muscular layer (Figure 4). After other diseases were ruled out and the clinical manifestations were combined with auxiliary examination results, the patient was diagnosed with UC.
We conducted sacrococcygeal magnetic resonance imaging (MRI) (Figure 5) and surgically removed the sacrococcygeal mass, then sent it for pathological examination after surgery. The pathological change was diagnosed as yolk sac tumor based on imaging, pathomorphology, and immunohistochemical results (Figure 6).
The patient underwent an emergency exploratory laparotomy as his intra-abdominal pressure kept increasing after having been administered anti-shock medication, gastrointestinal decompression, an indwelling anal canal to lower intra-abdominal pressure, and other treatments. The entire colon was found to be highly dilated during the surgery. Appendectomy + colonic irrigation via appendiceal catheterization + intestinal exteriorization + colonic biopsy was performed after the colonoscopy showed ulcers and numerous purulent masses in the colon. Intestinal exteriorization + abdominal wall suspension was performed due to an unachievable primary abdominal closure caused by intra-abdominal hypertension. The child underwent enteroscopy + return of exteriorized intestine + terminal ileostomy when the abdominal distension was relieved on the 7th day after surgery. Colonoscopy + sacrococcygeal mass resection was performed after excluding surgical contraindications. Colonoscopy indicated that intestinal inflammation continued to exist without significant improvement. Postoperative pathology of the sacrococcygeal mass indicated yolk sac tumor. The child was given 6 courses of JEB chemotherapy (etoposide: 120 mg/m2, vgtt, d1-3; carboplatin: 600 mg/m2, vgtt, d2; bleomycin: 15 mg/m2, vgtt, d3). Enteroscopy was performed for the fourth time after these 6 courses and showed that intestinal inflammation disappeared completely. Stoma closure after terminal ileostomy was then performed. The child was treated for about 1 year, was hospitalized 9 times, underwent 4 surgeries, and received 6 courses of chemotherapy.
Gastrointestinal symptoms of UC and TM in this patient completely disappeared after the sacrococcygeal YST resection, which was aided by postoperative chemotherapy. The child's body grew and developed well during the 7-year follow-up with no recurrence of the tumor, and no recurrence of ulcerative colitis. The follow-up is still ongoing.