Large intestine polyp (Cokic Polyp) is a general term for all protrusions into the intestinal cavity, including neoplastic and non-neoplastic types. The former is closely related to cancer development and is considered a precancerous lesion, while the latter has a lesser association with cancer. Since these two types of polyps are not easily distinguishable clinically, they are often initially diagnosed as polyps and further classified after pathological examination. Therefore, the term "large intestine polyp" in clinical practice does not specify the pathological nature of the polyp. Typically, the polyps referred to by clinicians are mostly non-neoplastic polyps, while neoplastic polyps are collectively referred to as adenomas.

bubble_chart Pathogenesis

1. Classification of large intestine polyps

There are many methods for classifying large intestine polyps. Currently, the most widely used classification both domestically and internationally is based on Morson's histological classification, which divides large intestine polyps into neoplastic, hamartomatous, inflammatory, and hyperplastic (Table 1). Additionally, polyps are classified based on their number as solitary or multiple.

The greatest advantage of this classification is that it collectively refers to neoplastic large intestine polyps as adenomas, while other non-neoplastic polyps are collectively referred to as polyps. Among these, the relationship between hamartomatous polyps and cancer is unclear, and they rarely undergo malignant transformation. Inflammatory and metaplastic polyps are unrelated to cancer, but some may evolve into adenomas. This classification clearly distinguishes the pathological nature of large intestine polyps, providing greater significance in guiding treatment.

The reported detection rates of various polyps vary greatly in the literature. Domestic reports indicate that adenomatous polyps are the most common, while Goldman abroad suggests that hyperplastic polyps are the most common polyps in the large intestine, with an incidence rate as high as 25-80%. Arthur believes that in adults, the incidence of hyperplastic polyps is at least 10 times higher than that of adenomas, whereas Franzin found during colonoscopy that the incidence of adenomas is three times that of hyperplastic polyps. Hermanek's analysis of 6378 polyps also supports Franzin's findings.

2. Large Intestine Polyp Anatomical Distribution

To determine the anatomical distribution characteristics of polyps, it is necessary to clearly segment the colon. In 1979, Rickert proposed dividing the large intestine into six segments based on percentage proportions. The initial 5% of the colon is the cecum, followed by the ascending colon (6-20%), transverse colon (21-50%), descending colon (51-65%), sigmoid colon (66-90%), and rectum (terminal 91-100% region). This segmentation has been widely used for describing and comparing the distribution of colon tumors in autopsy materials. In endoscopic biopsies, although the splenic flexure and hepatic flexure can be used for segmentation, the most common method is to divide the colon into the left (distal) and right (proximal) halves using the splenic flexure as the boundary. Using this method, the results from autopsy materials and endoscopic materials differ slightly. Autopsy findings show that polyps are evenly distributed throughout the colon, while colonoscopy reveals that polyps are predominantly found in the left side of the colon. It is speculated that polyps may initially occur mainly in the distal colon, which is supported by the fact that left-sided polyps are often more numerous than right-sided ones in autopsy materials. As age increases, polyps gradually shift from the left to the right side. Since the age structure of autopsy patients tends to be older, this results in a uniform trend in the incidence of intestinal tumors throughout the colon. In recent years, with the widespread use of fiber and electronic colonoscopy, the detection rate of left-sided intestinal tumors has also been increasing.

Most polyps have an insidious onset and may be clinically asymptomatic. Some larger polyps can cause intestinal symptoms, mainly changes in bowel habits, increased frequency of bowel movements, mucus in the stool or bloody mucus stools, occasional abdominal pain, and very rarely, a mass protruding from the anus during defecation. Some patients may experience long-term hematochezia or anemia. A family history often provides a clue to the diagnosis of polyps.

Some typical extraintestinal symptoms often suggest the possibility of polyposis, and some patients often seek medical attention due to extraintestinal symptoms, which should not be overlooked. For example, the presence of multiple bone tumors and soft tissue tumors should raise the possibility of Gardner syndrome, and the appearance of skin and mucous membrane pigmentation spots should suggest Peutz-Jeghers syndrome. Some authors point out that for patients suspected of having polyposis, even if there is no family history of polyps, a colonoscopy should be routinely performed to rule out the possibility of a syndrome.

Since large intestine polyps are often asymptomatic clinically, even when certain gastrointestinal symptoms such as abdominal distension and fullness, diarrhea, and constipation occur, they are usually mild and atypical and often overlooked. Patients generally seek medical attention due to hematochezia, bloody stools, or bloody mucus stools, and are often misdiagnosed with hemorrhoids or "dysentery," delaying necessary examinations. Therefore, the diagnosis of large intestine polyps first requires increasing physicians' awareness of the disease. Any unexplained hematochezia or gastrointestinal symptoms, especially in middle-aged and elderly men over 40 years old, should prompt further diagnostic examinations. This way, the detection and diagnosis rates of large intestine polyps can be significantly improved.

1. Although X-ray barium meal enema can sensitively detect large intestine polyps through the filling defect of barium, it often cannot correctly classify and characterize the lesions. Endoscopic examination not only allows direct observation of the subtle lesions of the large intestine mucosa, but also determines the nature of the lesions through tissue biopsy and cytological brush examination, making it the most important method for detecting and diagnosing large intestine polyps.

2. All polyps discovered during endoscopic examination must undergo biopsy to understand the nature, type, and presence of cancerous changes in the polyps. Small or pedunculated polyps can be removed using biopsy forceps or a snare for electroresection and then sent for examination, while large or broad-based polyps often can only undergo forceps biopsy.

3. Since the amount of villous components and the degree of atypical hyperplasia often vary in different parts of the same adenoma, the lesion at the biopsy site cannot fully represent the entire picture. The absence of cancerous changes at the biopsy site does not guarantee the absence of cancerous changes elsewhere in the adenoma. Therefore, the degree of atypical hyperplasia and the absence of cancerous changes in an adenoma often require the removal of the entire tumor and careful histological examination to confirm. The pathological results of forceps biopsy can be used for reference, but they are not the final conclusion. Clinically, discrepancies between preoperative forceps biopsy results and postoperative pathological diagnoses are quite common in villous adenomas. For example, Taylor's literature review reported that among 1140 cases of villous adenomas, 23-80% of cases that were benign in preoperative forceps biopsy were confirmed to have cancerous changes postoperatively. Clinicians must be aware of these limitations of adenoma forceps biopsy in diagnosis.

Currently, therapeutic endoscopy has made significant progress, and even some larger polyps can be removed endoscopically, providing convenience for pathological biopsy of polyps. For removed polyps, it is often required to include the stalk in the sample to comprehensively observe the histological morphology of the polyp. For large intestine adenomas, it is currently recommended to perform a complete tumor pathological examination to clarify the degree of atypical hyperplasia and avoid missing malignant changes. For composite polyps, since many coexist with adenomas, multiple tumor pathological examinations should be conducted, especially for polyps in multiple locations and in elderly patients. Even if it is not possible to perform pathological examination on every polyp, representative polyps from various locations should be sampled for biopsy to detect composite polyps, especially those with malignant potential.

bubble_chart Diagnosis

There are three ways to detect polyps. The most common is when patients are incidentally found to have polyps during visits for intestinal dysfunction (such as irritable bowel syndrome) or rectal bleeding. The second is through screening in asymptomatic populations. The third is when the polyp is large, and patients seek medical attention due to symptoms caused by the polyp itself, leading to its detection. Since polyps often lack clinical signs, detection through the third method is very limited.

bubble_chart Treatment Measures

The principle for managing large intestine polyps is to remove them upon detection. Currently, the primary methods for polyp removal involve various endoscopic techniques. Depending on the polyp's morphology, size, number, and the presence, length, and thickness of the stalk, different methods are employed: ① High-frequency electrocoagulation snare resection: mainly used for pedunculated polyps; ② High-frequency electrocoagulation ablation: primarily for multiple hemispherical small polyps; ③ High-frequency electrocoagulation hot biopsy forceps method: rarely used today, largely replaced by methods ② and ④; ④ Biopsy forceps removal: mainly for single or a few small spherical polyps, simple and convenient, and allows for pathological examination of the biopsy; ⑤ Laser qi transformation and microwave diathermy: suitable for cases where histological specimens are not required; ⑥ Mucosal stripping and embedding removal: mainly for flat polyps or early cancer patients; ⑦ "Close-contact" removal method: primarily for large polyps with long stalks that are difficult to suspend in the intestinal lumen, using close-contact electrocoagulation resection against the intestinal wall. Southern Hospital pioneered this method, removing 157 large polyps from 142 patients, with only 2 cases of grade I mucosal burns and no perforation complications. ⑧ Staged batch removal: mainly for patients with more than 10-20 polyps that cannot be removed in one session. ⑨ Combined endoscopic and surgical treatment: mainly for polyp patients, where sparse polyp areas are surgically removed, achieving both treatment goals and maintaining normal large intestine function.

Since large intestine polyps, especially adenomatous polyps, are widely recognized by scholars as precancerous lesions, regular follow-up for large intestine polyp patients has been elevated to the level of preventing early large intestine cancer. Southern Hospital followed up 252 patients over 10 years, including 184 with adenomatous polyps and 68 with inflammatory polyps, with initial follow-up positive rates of 51.0% and 34.2%, respectively. For negative patients re-followed, the positive rates were 9.8% for adenomas and 8.2% for inflammatory polyps; for positive patients re-followed, the positive rates were significantly higher, at 47.3% and 35.6%, respectively. Notably, 15 cases (8.2%) of adenomatous polyps remained positive after 4-7 follow-ups over 10 years, but none showed malignant transformation. This is closely related to the timely detection and removal of polyps during regular follow-ups. In the same period, one female patient with an adenomatous polyp refused removal, and two years later, symptoms became pronounced. A repeat colonoscopy revealed that the original adenoma had progressed to advanced cancer, necessitating surgical treatment. Therefore, regular follow-up for large intestine polyps, especially adenomatous polyps, is a crucial step in preventing malignant transformation.

The recurrence rate of polyps is relatively high, with foreign reports ranging from 13% to 86%. Newly detected polyps, apart from some being residual polyps that have regrown, include newly formed large intestine polyps and hereditary fistula disease polyps. To maintain a polyp-free state in the intestines and prevent the occurrence of large intestine cancer, it is necessary to establish an economical and effective follow-up schedule. Currently, there are various proposed follow-up schedules for adenomas internationally. Among these, the scheme discussed and recommended by the large intestine adenoma group at the Third International Large Intestine Cancer Conference held in Boston is quite detailed. They pointed out that the risk of new adenomas and local adenoma recurrence varies among patients after adenoma removal, and thus should be treated differently: single, pedunculated (or sessile but <2cm tubular adenomas) with mild or grade II atypical hyperplasia belong to the low-risk group. Those with any of the following conditions belong to the high-risk group: multiple adenomas, adenoma diameter >2cm, sessile villous or mixed adenomas, adenomas with grade III atypical hyperplasia or accompanied by carcinoma in situ, and adenomas with invasive cancer. The follow-up schedule for the high-risk group is adenoma removal, endoscopic examination at 3-6 months, if negative, another examination after 6-9 months, if still negative, an examination every year, and if still negative, an examination every 3 years, but with annual fecal occult blood tests during this period. For the low-risk group, a follow-up examination is conducted one year after adenoma removal, if negative, an examination every 3 years for a total of two times, then an examination every 5 years, but with annual fecal occult blood tests during the follow-up period. If polyps are found during the follow-up, endoscopic removal is performed immediately.