A colonoscopy is a medical procedure that provides a direct, visual examination of the large intestine, including the colon and the rectum. This examination uses a colonoscope, a long, flexible tube equipped with a light and a miniature video camera. The primary purpose is to inspect the inner lining of the bowel wall to identify abnormalities that may indicate digestive tract disease. By offering a comprehensive view of the entire colon, the procedure serves as a powerful screening and diagnostic tool for maintaining gastrointestinal health.
Detecting Precancerous Growths
One significant contribution of a colonoscopy is cancer prevention through the detection and removal of precancerous growths called polyps. A polyp is an abnormal cluster of cells forming on the inner lining of the colon or rectum. While most are benign, some types can eventually develop into malignancy. The procedure allows a physician to see these growths, which typically appear as small, raised bumps or patches on the mucosal surface. This visual identification interrupts the progression from a normal cell to a cancerous one.
Polyps are classified into groups that carry different risks for cancer development. Hyperplastic polyps are non-neoplastic, meaning they have a low risk of turning into cancer and are often found in the lower colon. In contrast, adenomatous polyps, which account for about 70 percent of all polyps, are neoplastic and are the precursor lesion for nearly all colorectal cancers. Sessile serrated polyps are a separate type of adenoma that are often flat and carry a high risk of malignant transformation.
When a polyp is detected, it is immediately followed by a polypectomy, the therapeutic removal of the growth during the same procedure. For smaller polyps, a doctor may use forceps to snip the tissue. Larger polyps often require a wire loop, known as a snare, to encircle the base and remove the growth. The snare technique often uses electrocautery (an electrical current) to cut the polyp and simultaneously seal blood vessels to prevent bleeding. All removed polyps are sent to a pathology lab for microscopic analysis to confirm the cell type, which dictates the interval for future surveillance.
Diagnosing Colorectal Cancer
When a malignancy is present, a colonoscopy is the definitive procedure for diagnosis. Cancerous tumors often present visually as large, fixed, or depressed lesions that exhibit fragility and spontaneous bleeding, distinguishing them from benign polyps. The visual signs of a suspicious mass prompt the physician to take a tissue sample, or biopsy, using specialized instruments passed through the colonoscope channel. This biopsy is the only way to obtain a definitive diagnosis of cancer.
The certainty of a cancer diagnosis rests on the histopathology report, where a pathologist examines the tissue sample under a microscope for malignant cells. The collected tissue is preserved and sliced thinly for detailed cellular analysis and assessment of the tumor’s depth of invasion. Visual characteristics observed during the procedure, such as a tumor size greater than 1 centimeter or a depressed shape, are highly suggestive of advanced pathology. However, the biopsy provides the necessary cellular confirmation for treatment planning.
Colonoscopy plays a crucial role in post-treatment surveillance for patients who have undergone curative resection for colorectal cancer. The goal of this follow-up is to detect any recurrence of the primary tumor or the development of a new cancer or precancerous polyp. Current guidelines recommend a high-quality clearing colonoscopy within a set period after surgery, followed by surveillance colonoscopies at specific intervals, such as one year later, and then typically every three to five years if findings remain clear. This structured monitoring is fundamental to preventing relapse and improving long-term survival.
Revealing Chronic Digestive Diseases
The endoscopic view provided by a colonoscopy is suited to diagnosing and differentiating chronic inflammatory conditions of the large bowel, known as Inflammatory Bowel Disease (IBD). The visual findings are distinct for the two main forms of IBD, Ulcerative Colitis (UC) and Crohn’s Disease (CD), which helps guide therapy. Ulcerative Colitis is typically limited to the mucosal layer of the colon and almost always begins in the rectum, extending proximally in a continuous pattern. Endoscopic signs of active UC include erythema (redness), friability (tissue that bleeds easily), and a loss of the normal vascular pattern due to inflammation.
In contrast, Crohn’s Disease (CD) is characterized by transmural inflammation, affecting all layers of the bowel wall. It is known for its discontinuous involvement, presenting as “skip lesions” interspersed with healthy tissue. The deep, full-thickness inflammation in CD often results in specific visual markers, such as deep, longitudinal ulcers and a characteristic “cobblestone” appearance caused by fissures separating swollen mucosa. Colonoscopy is also used to identify structural changes associated with IBD, such as strictures (narrowing of the colon) or the presence of pseudopolyps, which are remnants of inflamed tissue from chronic disease.
The procedure also identifies the common structural condition known as diverticulosis. Diverticulosis involves the formation of small, sac-like outpouchings, or diverticula, that protrude through the muscle layers of the colon wall. These pouches are frequently discovered incidentally during routine screening, especially in older adults. While usually asymptomatic, the presence of these diverticula can be a source of future complications, such as bleeding or inflammation (diverticulitis).
Identifying Causes of Bleeding and Structural Issues
A colonoscopy is frequently performed to investigate the source of unexplained gastrointestinal bleeding, which may not be related to polyps or chronic inflammation. One vascular abnormality often found is angiodysplasia, involving fragile, dilated blood vessels, usually located in the right side of the colon. These lesions appear endoscopically as small, bright red tufts of abnormal vessels that are prone to chronic blood loss, often leading to iron deficiency anemia.
The colonoscope allows for immediate therapeutic intervention on these bleeding lesions, typically using an endoscopic technique like argon plasma coagulation (APC). APC uses a jet of argon gas ionized by an electrical current to burn and seal the abnormal vessels, effectively stopping the hemorrhage. Colonoscopy is also used to identify non-IBD related ulcers, which may be caused by medications, infections, or ischemia (lack of blood flow). These ulcers are usually discrete and localized, differentiating them from the widespread patterns seen in IBD.
Furthermore, the procedure directly visualizes and can sometimes treat structural issues like strictures, which are areas of abnormal narrowing in the colon that can obstruct the passage of stool. While some strictures are a consequence of Crohn’s Disease, others may result from radiation injury, prior surgeries, or ischemic events. Using balloons passed through the scope, a physician can perform endoscopic dilation to widen the narrowed segment and restore normal function. The procedure’s ability to pinpoint the exact location and nature of acute or mechanical issues makes it an indispensable diagnostic and therapeutic tool.