A lower endoscopy is a medical procedure used to visualize the interior of the lower gastrointestinal tract, specifically the large intestine, which includes the colon and the rectum. The two main types are a colonoscopy, which examines the entire colon, and a flexible sigmoidoscopy, which focuses on the rectum and the lower part of the colon. This examination is performed using a thin, flexible tube called an endoscope, which has a light and a camera to transmit images to a monitor. The primary function of a lower endoscopy is direct visualization of the mucosal lining, which allows for the detection of abnormalities and the collection of tissue samples (biopsies) for laboratory analysis. This technique is fundamental for both screening symptom-free individuals and diagnosing the source of unexplained gastrointestinal symptoms, such as abdominal pain, rectal bleeding, or changes in bowel habits.
Detecting Neoplastic Changes
The most widely recognized application of lower endoscopy is in the detection and prevention of colorectal cancer, which is the third leading cause of cancer-related deaths in the United States. The procedure allows for the identification of precancerous growths called polyps, which arise from the inner lining of the colon. These growths, known as adenomas, are considered precursors to most colorectal cancers, meaning their removal prevents cancer from developing.
During a colonoscopy, any identified polyp is typically removed in a procedure called a polypectomy, often using a snare to excise the growth and cauterize the base to control bleeding. This intervention transforms the procedure from a diagnostic tool into a preventative one, significantly reducing the lifetime risk of cancer. Polyps are classified into various types, with adenomas being the most concerning for cancer risk.
Endoscopy also helps distinguish between adenomatous polyps, which have malignant potential, and non-neoplastic polyps, such as hyperplastic polyps. Advanced techniques, including narrow-band imaging (NBI) and chromoendoscopy, use specialized light filters or dyes to enhance the visual details of the mucosal surface. These enhancements allow endoscopists to better classify polyps in real-time and predict their histology with high accuracy before a laboratory biopsy confirms the diagnosis. By identifying and removing these early-stage lesions, colonoscopy serves as the gold standard for colorectal cancer screening.
Diagnosing Chronic Inflammatory Bowel Disease
Lower endoscopy is a fundamental tool for establishing the initial diagnosis and monitoring the long-term course of chronic inflammatory bowel disease (IBD), which includes Ulcerative Colitis (UC) and Crohn’s Disease (CD). These conditions are characterized by chronic inflammation of the gastrointestinal tract, and endoscopy provides an objective, direct view of the severity and pattern of this inflammation. The visual evidence helps to differentiate between the two main types of IBD: UC typically affects only the colon and starts in the rectum, progressing continuously, while CD can affect any part of the digestive tract and often presents with patchy areas of inflammation.
During the procedure, the endoscopist can observe specific signs of active disease, such as mucosal redness, swelling, loss of the typical vascular pattern, and the presence of erosions or ulcers. In cases of suspected CD, a colonoscopy is typically performed with intubation of the terminal ileum, as this is a common site for Crohn’s disease involvement. Biopsies are taken from both affected and seemingly normal areas to confirm the diagnosis and to assess the microscopic extent of the disease.
The procedure is also used for ongoing surveillance in IBD patients, particularly for monitoring disease activity and response to treatment. Chronic inflammation increases the risk of developing dysplasia and colorectal cancer. Regular endoscopic examinations allow doctors to monitor for these complications and assess for complications like strictures, which are areas of narrowing in the intestine caused by scarring.
Identifying Structural and Vascular Abnormalities
Lower endoscopy is highly effective at identifying structural defects and vascular malformations that can be the source of unexplained symptoms or gastrointestinal bleeding. One common structural finding is diverticulosis, which are small, outward-facing pouches or sacs that develop in the wall of the colon. While diverticulosis itself is often asymptomatic, it is the most frequent cause of significant lower gastrointestinal bleeding.
The endoscope can also directly visualize angiodysplasia, which are abnormal, fragile, dilated blood vessels near the mucosal surface of the colon. These vascular lesions, often seen as small, flat, cherry-red spots, are a common cause of recurrent, low-grade bleeding that can lead to iron deficiency anemia. Angiodysplasia is the second leading cause of lower gastrointestinal bleeding in older patients, and colonoscopy often allows for immediate endoscopic treatment, such as thermal coagulation, to stop the hemorrhage.
The procedure also helps to evaluate the source of rectal bleeding, often distinguishing between a higher, more serious source and a more common, low-lying cause, such as internal hemorrhoids. Hemorrhoids are swollen veins in the rectum or anus that can be visualized during the procedure. Identification of these structural and vascular issues helps target treatment and rule out more serious underlying conditions.
Evaluating Causes of Acute Colitis
Lower endoscopy plays a role in evaluating the causes of acute, non-chronic inflammation of the colon, generally termed acute colitis. This inflammation often presents with sudden-onset diarrhea and abdominal pain, frequently accompanied by bleeding. The procedure is used to determine the cause and extent of the inflammation, which can stem from several distinct etiologies.
Infectious colitis, caused by pathogens like Clostridium difficile, is a common cause, and the endoscope can reveal the characteristic appearance of pseudomembranes on the colon wall. The procedure is also used to diagnose ischemic colitis, which results from a temporary lack of blood flow to a segment of the colon. In ischemic cases, the colon lining may appear pale, fragile, and edematous with characteristic segmental involvement.
Endoscopy is also useful for identifying drug-induced colitis, which can be triggered by various medications, including nonsteroidal anti-inflammatory drugs (NSAIDs). In all forms of acute colitis, a targeted biopsy obtained during the procedure is necessary to differentiate the specific cause, such as distinguishing infectious from ischemic injury. While most cases of ischemic colitis are transient and self-limiting, endoscopy is essential for recognizing the signs of more severe injury that might require urgent intervention.