Crohn’s disease is an inflammatory disease of the intestine of unknown origin that can occur anywhere in the gastrointestinal tract, but is more prevalent in the terminal ileum and right hemicolectum. The disease and chronic nonspecific ulcerative colitis are collectively referred to as inflammatory bowel disease (IBD). The disease is also known as restrictive enteritis, restrictive ileitis, segmental enteritis, and granulomatous enteritis. The lesions are confined to the small intestine (mainly the terminal ileum) and the colon, or both, and are often ileal and right hemicolectomy lesions. The pathological changes are divided into the acute inflammatory phase, the ulcerative phase, the stricture phase, and the fistula formation phase (perforation phase). In the acute phase, edema and inflammation of the intestinal wall predominate; in the chronic phase, the intestinal wall is thickened and stiffened, and the affected intestinal canal has a tubular shape with dilatation at its upper end. Typical lesions on the mucosal surface are: 1. ulcers: early shallow small ulcers, then become longitudinal or transverse ulcers, longitudinal ulcers deep into the intestinal wall that form a more typical cleavage furrow, distributed along the mesenteric side, the intestinal wall may have abscesses. 2. Onycholithiasis nodules. Due to the submucosal edema and cellular infiltration of the formation of small islands of protrusion, coupled with the contraction of fibrosis and scarring after ulcer healing, the mucosal surface resembles pebbles. 3, granuloma: no caseous changes, distinct from tuberculosis. 4.Fistula and abscess: The fissure in the intestinal wall is essentially a penetrating ulcer that causes adhesions and abscesses between the intestinal canal and the intestinal canal, the intestinal canal and organs or tissues (such as the bladder, vagina, mesenteric or retroperitoneal tissues, etc.), and forms an internal fistula. If the lesion penetrates the intestinal wall and passes outside the body through the abdominal wall or perianal tissues, an external fistula is formed. Clinical manifestations include abdominal pain, diarrhea, abdominal masses, fistula formation and intestinal obstruction, which may be accompanied by fever, anemia, nutritional disorders and extraintestinal damage to joints, skin, eyes, oral mucosa and liver. The disease can be recurrent and persistent. 1. Gastrointestinal manifestations: (1) Abdominal pain is located in the right lower abdomen or around the umbilicus, with spasmodic pain, intermittent episodes, accompanied by intestinal tinnitus, aggravated after meals and relieved after defecation. If the abdominal pain persists and the pressure pain is obvious, it suggests that the inflammation has spread to the peritoneum or the abdominal cavity and formed an abscess. Severe pain throughout the abdomen and abdominal muscle tension may be due to acute perforation of the diseased intestinal segment. (2) Diarrhea is caused by inflammatory exudation, increased peristalsis and secondary malabsorption in the diseased intestinal segment. It starts with intermittent episodes and later becomes a persistent paste-like stool without pus, blood or mucus. If the lesion involves the lower part of the colon or rectum, there may be mucus and blood stools and a feeling of urgency. (3) Abdominal masses are more common in the right lower abdomen and around the umbilicus and are caused by intestinal adhesions, thickening of the intestinal wall and mesentery, enlarged mesenteric lymph nodes, internal fistula or local abscess formation. (4) Fistula formation is one of the clinical features of Crohn’s disease. Fistulae are formed by transmural inflammatory lesions that penetrate the entire intestinal wall to extraintestinal tissues or organs. Internal fistulae may lead to other intestinal segments, mesentery, bladder, ureter, and retroperitoneum of the vagina. External fistulas lead to the abdominal wall or perianal skin. （A few patients have perianal and perirectal fistulae, abscess formation, anal fissures and other lesions. Systemic manifestations (1) Fever is caused by intestinal inflammatory activity or secondary infection, often intermittent low or moderate fever, a small number of flaccid fever, may be accompanied by toxemia. (2) Nutritional disorders due to loss of appetite, chronic diarrhea and chronic wasting diseases, anemia, hypoproteinemia, vitamin deficiency, calcium deficiency, osteoporosis, etc. (3) Disorders of water, electrolytes and acid-base balance during acute attacks. (3) Extra-intestinal manifestations Some patients have iridocyclitis, uveitis, pestle finger, arthritis, nodular erythema gangrenosum pyoderma, oral mucosal ulcers, chronic hepatitis, small bile duct perichondritis, sclerosing cholangitis, etc. Occasionally, amyloidosis or thromboembolic disease is seen. Colonoscopy is the most sensitive test for the diagnosis of Crohn’s disease. The main risks are intestinal perforation and bleeding.