Polip Kolon

01Pathophysiology

Colon polyps are abnormal tissue growths that protrude from the colonic mucosa into the lumen. The clinical significance of a polyp depends entirely on its histological type, because neoplastic polyps carry premalignant potential while non-neoplastic polyps generally do not.
The central concept tested on exams is the adenoma-carcinoma sequence. This is the stepwise molecular pathway through which normal colonic epithelium transforms into invasive carcinoma. The initiating event is a loss-of-function mutation in the APC tumor suppressor gene on chromosome 5q21, which disrupts regulation of the Wnt signaling pathway and allows uncontrolled cell proliferation, forming an adenomatous polyp. Subsequent accumulation of oncogene activation (KRAS mutation) and further tumor suppressor losses (TP53, DCC/SMAD4) drive progression from low-grade dysplasia to high-grade dysplasia and ultimately to invasive adenocarcinoma. This entire process typically takes 10 to 15 years, which is the biological rationale behind the 10-year interval for average-risk screening colonoscopy.
The three features that increase an adenomatous polyp's risk of harboring or progressing to carcinoma are (1) villous histology, (2) size greater than 2 cm, and (3) high-grade dysplasia. This triad should be committed to memory. Villous adenomas have finger-like projections with a large surface area of dysplastic epithelium, explaining both their higher malignant potential and their tendency to secrete large volumes of mucus rich in protein and electrolytes. This mucous hypersecretion is the direct mechanism behind the classic presentation of secretory diarrhea with profound hypokalemia seen with large rectal villous adenomas.
A separate molecular pathway exists for serrated polyps. Sessile serrated lesions (previously called sessile serrated adenomas) arise through the serrated neoplasia pathway, involving BRAF mutation and CpG island methylator phenotype (CIMP), leading to epigenetic silencing of the MLH1 mismatch repair gene. These lesions are flat, pale, and covered with a mucous cap, making them notoriously difficult to detect on colonoscopy. They are predominantly found in the right (proximal) colon and account for a significant proportion of "interval" colorectal cancers that appear between screening examinations.
Hyperplastic polyps, by contrast, result from decreased epithelial apoptosis without true dysplasia. They are small (typically less than 5 mm), located in the rectosigmoid colon, and carry no independent malignant potential. Their only importance on exams is as a distractor when contrasted with sessile serrated lesions.
In hereditary polyposis syndromes, the pathophysiology is driven by germline mutations. In Familial Adenomatous Polyposis (FAP), a germline APC mutation means one allele is already inactivated at birth; loss of the second allele (Knudson's two-hit hypothesis) occurs readily across the entire colon, producing hundreds to thousands of adenomatous polyps by adolescence and a near 100% lifetime risk of colorectal cancer if left untreated. In Lynch syndrome, germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2) lead to microsatellite instability (MSI), accelerating the accumulation of frameshift mutations and allowing cancer to develop from fewer and smaller adenomas, often in the right colon, at younger ages.

02Classification and Clinical Manifestation

Hereditary Polyposis Syndromes:

03Diagnostic Workup

The best initial test for a patient with suspected colonic polyps or positive screening is a colonoscopy. This is one of the uncommon situations where the best initial test and the gold standard are the same procedure, because colonoscopy allows both visualization and simultaneous polypectomy with tissue sampling. When a vignette describes a patient with a positive FIT or stool DNA test, the next best step is always a colonoscopy, never a repeat stool test or imaging.
During colonoscopy, polyps are classified by their Paris classification morphology (pedunculated, sessile, flat, or depressed), which guides the endoscopic removal technique. All removed polyps are sent for histopathological examination, which is the definitive test that determines clinical management. Pathology answers two critical questions: (1) is this an adenomatous/serrated polyp (premalignant) or a non-neoplastic polyp, and (2) if adenomatous, is there high-grade dysplasia or invasive carcinoma at the resection margin?
For screening in average-risk patients starting at age 45, any of the following is acceptable: colonoscopy every 10 years, annual FIT, FIT-DNA every 1 to 3 years, or CT colonography every 5 years. However, colonoscopy is the only modality that is simultaneously diagnostic and therapeutic. If any non-colonoscopy screening test is positive, the next step is always colonoscopy.
For hereditary syndrome workup, genetic testing is the confirmatory study. When FAP is suspected (>100 adenomatous polyps or a known family history), APC gene sequencing confirms the diagnosis. When Lynch syndrome is suspected (young patient, right-sided cancer, strong family history meeting Amsterdam II criteria or Bethesda guidelines), the tumor tissue should be tested for microsatellite instability (MSI) and immunohistochemistry (IHC) for mismatch repair proteins first, followed by germline genetic testing if abnormalities are found.

04Management and Treatment

Acute stabilization is relevant when a polyp presents with bleeding. Most post-polypectomy or polyp-related bleeding responds to endoscopic hemostasis (clips, electrocautery, injection of epinephrine). If bleeding is hemodynamically significant, initial resuscitation with IV fluids and blood transfusion should precede endoscopy. Urgent colonoscopy is the next step once the patient is stabilized.
For long-term management, the surveillance interval is the most commonly tested concept. The logic is straightforward: the higher the risk features of the removed polyp (larger size, villous component, high-grade dysplasia, greater number), the shorter the surveillance interval. Exam questions will test whether you can assign the correct follow-up interval based on pathology results.
A frequently tested principle is that NSAIDs (sulindac, celecoxib) reduce polyp burden in FAP but do not replace the need for surgery. A vignette describing a patient with FAP who is "on celecoxib" and then asks about the next best step is testing whether you know that prophylactic colectomy is still required.
Contraindications and caveats: In patients on anticoagulation or antiplatelet therapy, the decision to hold or continue these agents before polypectomy depends on the thromboembolic risk versus bleeding risk. Low-risk polypectomy (cold snare for small polyps) can often be performed without interrupting anticoagulation. Hot snare polypectomy and EMR typically require temporary cessation of anticoagulants. This is a clinical judgment question that occasionally appears on exams.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap with colon polyp questions is confusing the surveillance interval based on polyp histology. Students frequently default to "repeat colonoscopy in 3 years" for all adenomas, but low-risk adenomas (1 to 2 small tubular adenomas without high-grade dysplasia) now warrant a 7 to 10 year interval per current guidelines, while high-risk findings (villous histology, high-grade dysplasia, size greater than 10 mm, 3 or more adenomas, or sessile serrated lesions with dysplasia) require a 3-year follow-up. Getting this wrong is a reliable way to lose a point.
A second high-yield trap involves the villous adenoma with secretory diarrhea. When a vignette describes an older patient with watery diarrhea and hypokalemia, students often jump to infectious or endocrine causes. The key is to recognize that a large rectal villous adenoma can produce enough mucous secretion to cause clinically significant volume and electrolyte loss. The combination of "rectal mass" and "hypokalemia" should immediately trigger this diagnosis.
Third, students commonly confuse sessile serrated lesions with hyperplastic polyps. Both have a serrated architecture on histology, but the sessile serrated lesion has basal crypt dilation and horizontal (boot-shaped or L-shaped) crypts, is located in the right colon, is premalignant through the BRAF/CIMP pathway, and requires surveillance. A hyperplastic polyp is small, sits in the rectosigmoid, and requires nothing. The exam will test whether you can distinguish these two, because the management is entirely different.
Fourth, for FAP, remember that celecoxib and sulindac reduce polyp number but do not eliminate cancer risk. The definitive management is prophylactic total proctocolectomy. A vignette that describes a patient with FAP "already taking celecoxib" and asks what additional step is needed is testing whether you know surgery is still mandatory.
Finally, Lynch syndrome is tested differently from FAP. Lynch syndrome does not present with hundreds of polyps. It presents with early-onset, right-sided colorectal cancer from a small number of adenomas that progress quickly due to defective mismatch repair. The clues in the vignette are young age, proximal colon cancer, a strong family history meeting Amsterdam II criteria (3 relatives with Lynch-associated cancers across 2 generations, with at least 1 diagnosed before age 50), and tumor testing positive for microsatellite instability. If you see "carpet of polyps," think FAP. If you see "young patient, right-sided cancer, strong family history," think Lynch syndrome.
The core competency being tested across all colon polyp questions is whether you can integrate pathology results, risk stratification, and guideline-based surveillance into a coherent management plan, and whether you can distinguish between hereditary syndromes based on their unique genetic, histological, and clinical profiles.