A colonoscopy uses a long, flexible tube called a colonoscope to examine the entire inner lining of the large intestine and rectum. This instrument contains a camera and light source, providing a clear, magnified visual inspection of the mucosal surface. The procedure requires thorough cleansing of the bowel beforehand to ensure maximum visibility for an accurate examination. Serving as both a powerful diagnostic tool and a preventative measure, the colonoscopy allows a physician to identify and often immediately address abnormalities within the lower gastrointestinal tract.
Screening for and Identifying Neoplastic Changes
The primary function of a colonoscopy is to interrupt the development of colorectal cancer by targeting precancerous growths known as polyps. Most colorectal cancers arise from these lesions through a process termed the adenoma-carcinoma sequence, which can take a decade or more to complete. The procedure is effective because it allows for the simultaneous identification and removal of these polyps (polypectomy) before they become malignant. Polyps found during screening are typically classified as adenomas, hyperplastic polyps, or sessile serrated lesions, each carrying a different potential for cancerous transformation.
Adenomatous polyps are the most common type with malignant potential, appearing as raised growths with a distinct stalk (pedunculated) or a broad base (sessile). A more subtle precursor is the sessile serrated lesion (SSL), which is typically flat, pale, and may be covered with a characteristic mucus cap, making them challenging to detect. These SSLs follow an alternative, sometimes faster, pathway to cancer development. Once a polyp is identified, it is immediately removed using specialized tools passed through the colonoscope, such as a cold snare for smaller lesions, thereby preventing future cancer.
When a malignant tumor is present, the colonoscopy reveals a colorectal cancer mass, which typically appears as a firm, irregular, ulcerated, or bulky growth protruding into the colon’s lumen. The visual characteristics of the mass, such as its size, location, and friability (tendency to bleed when touched), guide the physician’s assessment. Biopsies are performed to confirm the presence of cancer cells and determine the specific type of malignancy. This immediate tissue analysis is fundamental for accurate diagnosis and subsequent staging and treatment planning.
Diagnosing Chronic Inflammatory Bowel Conditions
The colonoscopy diagnoses and differentiates the two main types of chronic inflammatory bowel disease (IBD): Ulcerative Colitis (UC) and Crohn’s Disease (CD). These conditions present with distinct visual patterns on the colon lining. In Ulcerative Colitis, the inflammation is typically continuous, starting at the rectum and extending proximally without interruption. Endoscopic signs include loss of the normal fine vascular pattern, a granular or red (erythematous) mucosal surface, and superficial ulcerations.
In contrast, Crohn’s Disease is characterized by inflammation that is patchy, meaning areas of diseased tissue are interspersed with sections of healthy lining, known as “skip lesions.” This condition can also affect the entire thickness of the bowel wall (transmural inflammation), unlike UC, which is confined to the inner mucosal layer. Crohn’s-specific findings include deep, linear, or longitudinal ulcers, which, when combined with surrounding edematous mucosa, can create a distinctive “cobblestoning” appearance. The procedure also allows for targeted biopsies of inflamed areas to confirm the specific inflammatory pattern and rule out other causes.
The ability to directly visualize the extent and pattern of inflammation determines disease severity and guides therapeutic choices. Repeated colonoscopies also play a role in surveillance for patients with long-standing IBD, as chronic inflammation increases the risk of developing colorectal dysplasia and cancer. The procedure can identify complications of IBD, such as pseudopolyps, which are inflamed, regenerating mucosal tags that remain after severe ulceration.
Revealing Structural and Vascular Anomalies
Beyond neoplastic and inflammatory diseases, a colonoscopy reveals structural and vascular anomalies that can be the source of a patient’s gastrointestinal symptoms. One common structural finding is diverticulosis, characterized by the presence of small, outward-pouching sacs in the colon wall. While diverticulosis itself is usually asymptomatic, the procedure can sometimes identify signs of diverticulitis, which is the inflammation or infection of these pouches, or pinpoint a bleeding diverticulum as the cause of acute hemorrhage.
Another finding is angiodysplasia, which involves small, fragile, and dilated blood vessels near the mucosal surface. These lesions typically appear as small, fern-like, flat red spots, often located in the right side of the colon, particularly the cecum. Angiodysplasia is a frequent cause of lower gastrointestinal bleeding that may lead to chronic iron-deficiency anemia. The colonoscopy provides the opportunity to treat these lesions immediately using thermal energy or other cauterization techniques to stop the bleeding.
The procedure can also reveal strictures, which are narrowings of the colon lumen resulting from scarring due to prior inflammation, surgery, or an underlying malignancy. A stricture’s appearance helps the physician determine its likely cause; for instance, long, deep strictures are typical of advanced Crohn’s disease, while a short, rigid narrowing might raise suspicion of cancer. Finally, the colonoscopy provides a method for locating the precise source of any acute or chronic gastrointestinal bleeding, whether it originates from ulcers, hemorrhoids, or the lesions previously mentioned.