The large intestine is an important part of the digestive system and is the lower part of the digestive tract. The adult large intestine is about 1.5m long, starting from the ileum and including six parts: cecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum. The entire length is shaped like a box, surrounding the jejunum and ileum.
Colorectal cancer comes from colonic mucosal cells. Under the action of carcinogenic factors, these colonic mucosal cells proliferate uncontrollably and keep growing to form masses. Colorectal cancer not only attacks the intestinal wall locally, but also can cause systemic metastasis through lymph or blood, which is a disease seriously endangering people’s health. The incidence and mortality rate of colorectal cancer are increasing year by year in China, and the increasing trend is more obvious in cities.
I. Classification.
Colon cancer can be divided into colon cancer and rectal cancer according to anatomical parts, of which rectal cancer accounts for about 2/3. colon cancer can be divided into cecum cancer, ascending colon cancer, colon liver flexure cancer, transverse colon cancer, colon splenic flexure cancer, sigmoid colon cancer, etc.
II. Causes of incidence.
At present, it is believed that there are mainly the following reasons.
1, dietary factors. Dietary factors refer to high protein, high fat and low fiber diet. In China, with the improvement of living standard, high-fat diet has become the mainstream, resulting in the incidence of colorectal cancer in China increasing year by year. Fibrous foods include: fresh vegetables, fruits and coarse grains. Studies have found that eating fresh vegetables, fruits and coarse grains can significantly reduce the occurrence of colorectal cancer.
2. Genetic factors. All colorectal cancers are influenced by genetic factors. Individuals with first-degree relatives with colorectal cancer have 2-4 times higher risk of colorectal cancer than those without family history. In addition, patients with familial adenomatous polyposis can have hundreds or thousands of adenomas in the colon, and over time, people with this disease will sooner or later become cancerous, and many members of the family have the same disease. Once the disease is detected, the patient and his or her immediate family need to be followed up for a long time to do the necessary tests.
3.Adenomatous polyps. First of all, we need to clarify what is “polyp”. Polyps are various kinds of bulges that grow on the mucosal surface of the intestine. Medically speaking, there are two kinds of polyps: tumor and non-tumor. The former is called “adenoma”, which is a real benign tumor. The latter type of polyps are not tumors, including inflammatory polyps and hyperplastic polyps, which are not related to the occurrence of cancer. Adenomatous polyps are benign lesions, but they are closely related to colorectal cancer. When the polyp grows bigger, it may become cancerous, and the cancer rate is as high as 30% when the polyp is larger than 2cm. In addition, the cancer rate of villous adenoma is much higher than that of tubular adenoma.
4.Chronic inflammation of the colon. Patients suffering from ulcerative colitis and Crohn’s disease are more likely to be transformed into cancer the longer the disease lasts, and their risk of colorectal cancer is 4~20 times of the general population
5.Other. Obesity, lack of exercise, smoking and alcohol consumption are also prone to colorectal cancer.
III. Symptoms.
Early colorectal cancer has no symptoms or mild symptoms, so it is easy to be ignored. It is only when the tumor progresses and becomes bigger that it will produce obvious symptoms, and the treatment effect at that time is already greatly reduced compared with the early stage. Colorectal cancer mainly has the following manifestations.
1.Blood in stool. Blood in stool is the most common symptom of colorectal cancer, and also the main reason for patients to seek medical consultation. To a certain extent, colorectal cancer will become erosion, necrosis and rupture, which will lead to blood in stool. A small amount of blood in stool has no obvious symptoms, but only a positive fecal occult blood test. When the bleeding reaches a certain amount, there may be blood in the stool or blood in the stool. The color of the blood in the stool varies depending on the location of the bleeding and how long the blood remains in the intestine. The blood may be mixed with stool or may adhere to the surface of the stool. In severe cases, there may be a large amount of blood in the stool. The symptoms of blood in the stool are most likely to be confused with hemorrhoids and misdiagnosed.
2.Pus and mucus stool. Sometimes colorectal cancer is manifested as pus and blood stool, which is a mixture of blood and mucus, and is discharged in the form of jelly. Laboratory tests can show pus cells, white blood cells and red blood cells, similar to dysentery. Some colorectal cancers can produce a large amount of mucus discharged with stool, which can be easily misdiagnosed as enteritis.
3.Change in stool habit and stool characteristics. In other words, the original defecation pattern is disrupted, manifested as increased number of stools or even diarrhea, or decreased number of stools, or alternating diarrhea and constipation. In the case of increased stool frequency, the number of bowel movements may reach dozens of times a day, but the volume is small each time, and there is always a feeling that the stool is not clean. If the stool frequency decreases, it may be a sign of intestinal obstruction. The appearance of the stool can also change, such as thinning of the stool or see obvious grooves.
4.Abdominal pain. Abdominal pain is not very prominent and not characteristic in early or even mid-stage colorectal cancer. It can be irregular hidden pain or dull pain. The emergence of obvious paroxysmal colic often indicates that the tumor has narrowed the intestinal lumen and produced obstruction. Sudden severe pain in the whole abdomen may be due to perforation of intestinal cavity, while persistent dull pain is due to extensive invasion of abdominal cavity by tumor.
5. Abdominal mass. More than half of the patients with colon cancer may have masses in the abdomen, which is sometimes the main symptom of patients visiting the clinic. The site of the mass is basically the same as the site of tumor occurrence, but sometimes the mass can move widely, which makes it difficult to judge the site of tumor. In low rectal cancer, the lump can be palpated by the doctor through the rectum, but it is difficult to be detected by the patient. The movement of tumor often indicates that it can be removed by surgery. When the tumor invades the surrounding organs, the position of the mass is fixed and difficult to move.
6. Chronic wasting performance. Such as anemia, emaciation, weakness, etc. Some colorectal cancers have anemia as the prominent symptom, which should be noticed.
It should be noted that the above symptoms do not necessarily appear in one patient at the same time. Some symptoms may be more prominent while others are milder or even absent, which is related to the location and speed of tumor growth.
IV. Diagnosis.
1.Fecal occult blood test. Although this test is not specific for the diagnosis of this disease, it is a simple and easy method, and can be used as a screening tool for census and provide clues for early diagnosis.
2.Finger diagnosis of rectum. Most of rectal cancers can be palpated during rectal examination.
3.Fiber colonoscopy. Colonoscopy can clearly observe the whole colon, and can take suspicious lesions for pathological examination under direct vision, which is conducive to the detection and confirmation of early and micro colon cancer, and can further improve the correct diagnosis rate of this disease, which is the most important examination means of colorectal cancer.
4.Barium enema. It can detect lesions with a diameter of 1cm or more. In case of combined incomplete intestinal obstruction, laxative should be given after enema to prevent aggravating obstruction.
5.B ultrasound. It is mainly used to find out whether there is liver metastasis, whether there is enlargement of mesenteric lymph nodes and the relationship between tumor and adjacent organs. Intra-rectal ultrasound can accurately understand the depth of rectal cancer infiltration and lymph node metastasis.
6.CT and magnetic resonance imaging (MRI). Preoperative CT/ MRI is helpful for the diagnosis of liver metastasis. In addition, it can also show the tumor, especially the extent of the lesion and the relationship with the neighboring organs.
CEA is a glycoprotein that is often found in the serum of patients with malignant tumors and is not a specific antigen for colorectal cancer, therefore, serum CEA measurement is not specific for the diagnosis of this disease. If colorectal cancer is completely removed by surgery, the serum CEA will gradually decrease; if it recurs, it can rise again.
V. Treatment methods.
Surgical resection is the only curable treatment for colorectal cancer. The treatment principle of colorectal cancer is based on radical surgery, combined with chemotherapy, radiotherapy, immunotherapy and other means of comprehensive treatment.
1.Commonly used surgical procedures for radical colon cancer include
① Right hemicolectomy: it is suitable for cecum, ascending colon and hepatic flexure colon cancer. The scope of resection includes ascending colon, right half of transverse colon, 10-15 cm of terminal ileum and corresponding mesentery, and then transverse colon ileal anastomosis is performed.
② Transverse colectomy: suitable for cancer of the middle transverse colon. The scope of resection includes the entire transverse colon including the hepatic flexure and splenic flexure of the colon. Inter-colonic anastomosis is performed.
③Left hemicolectomy: suitable for cancer of splenic flexure and descending colon. The scope of resection includes the left half of transverse colon, descending colon, part or all of sigmoid colon.
④Radical sigmoid colon resection: suitable for sigmoid colon cancer. The resection area includes the sigmoid colon, part of the rectum and part of the descending colon. If the location of tumor is high, left hemicolectomy is feasible.
2.The common surgical procedures for radical surgery of rectal cancer are
(1) Pre-rectal resection (Dixon operation): it is the most widely used in clinical practice and can be applied to most rectal cancers above 5cm from the anal verge. Since the anal rectal ring is preserved intact, the patient has better postoperative anal function, which is the most ideal anus-preserving procedure at present.
(2) Combined abdominal perineal resection (Miles procedure): In principle, this procedure is suitable for low rectal cancer that is difficult to preserve anus, and is mainly used for low rectal cancer within 5 cm from the anal verge. This operation requires a permanent colostomy in the lower left abdomen due to the removal of the anus.
Palliative surgery For advanced cases with extensive metastasis and impossible to obtain radical cure, palliative resection and short-circuit surgery, colostomy, etc. can be pursued to relieve obstruction and other symptoms.