A colonoscopy is a medical procedure used to internally examine the entire length of the large intestine, including the colon and the rectum. The examination utilizes a specialized instrument called a colonoscope, a long, flexible tube equipped with advanced visualization capabilities. This procedure is primarily performed to screen for and prevent colorectal cancer by identifying and removing precancerous growths called polyps. It also serves to investigate symptoms like unexplained rectal bleeding, chronic diarrhea, or abdominal pain, helping to diagnose conditions such as inflammatory bowel disease.
Anatomy of the Colonoscope
The colonoscope is designed to be flexible yet maneuverable through the curved anatomy of the large bowel. It is a long, slender tube, typically measuring between 160 and 180 centimeters in length and 1.0 to 1.2 centimeters in diameter, inserted into the rectum. This flexible shaft contains multiple internal channels that allow the physician to perform various functions during the examination.
At the tip of the scope is a high-definition video chip, which transmits real-time images to an external monitor. Adjacent to the camera are light guides that illuminate the colon’s interior, ensuring the mucosal lining is visible. The scope also houses channels for water irrigation to clean the lens, and for air or carbon dioxide insufflation to gently distend the colon for a better view. A dedicated working channel allows the passage of accessory instruments, such as biopsy forceps for tissue samples or snares for polyp removal.
Preparing for the Procedure
The success of a colonoscopy depends entirely on the cleanliness of the colon, requiring a rigorous pre-procedure preparation process. Several days before the appointment, the patient must switch to a low-fiber diet, avoiding whole grains, nuts, seeds, and raw fruits and vegetables. This dietary restriction reduces the solid waste content in the bowel.
The day before the colonoscopy, the diet must be restricted only to clear liquids, such as water, broth, clear juices, and plain tea or coffee. Patients must avoid liquids colored red, blue, or purple, as these pigments can stain the colon lining and be mistaken for blood. This clear liquid phase ensures no solid material is introduced before the final cleansing.
The most intensive step is the prescribed bowel preparation solution, a powerful laxative that induces purging to completely empty the colon. This preparation is often administered as a “split prep,” with the first dose taken the evening before and the second dose consumed several hours before the procedure. Successful preparation results in a watery, clear effluent, confirming the colon’s lining is visible for inspection.
How the Procedure is Performed
On the day of the procedure, the patient is positioned on their side with knees drawn toward the chest, and an intravenous line is started for sedating medication. While some patients receive conscious sedation to remain relaxed but aware, many undergo deep sedation, allowing them to sleep comfortably through the process. The physician begins the examination by gently inserting the lubricated colonoscope into the rectum.
The scope is carefully guided through the large intestine, past the sigmoid colon and anatomical flexures, until it reaches the cecum, where the large and small intestines meet. To create space for viewing, the physician uses the air/water channel to insufflate the colon with either air or carbon dioxide (CO2). CO2 is preferred because it is absorbed by the body faster than air, potentially leading to less post-procedure bloating.
The most detailed part of the examination occurs as the physician slowly withdraws the colonoscope, scrutinizing the mucosal surface for abnormalities. If a polyp or suspicious lesion is identified, specialized instruments are passed through the working channel to remove the growth, a process known as a polypectomy. The removed tissue is retrieved and sent to a pathology lab for analysis to determine if it is benign or precancerous.
Immediate Post-Procedure and Results
Once the colonoscope is removed, the patient is transferred to a recovery area where nurses monitor vital signs while the effects of the sedative wear off. Patients may feel groggy and tired for a few hours; common side effects include bloating and cramping due to residual gas used for insufflation. Walking gently can help the body expel this gas more quickly.
Due to the lingering effects of the sedation, the patient must have a responsible adult present to drive them home after discharge. For the next 24 hours, patients must avoid driving, operating machinery, or making significant decisions until the medication is cleared from the system. The physician usually provides immediate preliminary findings before discharge, explaining whether the colon was clear or if polyps were removed.
If tissue samples or polyps were collected, the final pathology results, which provide a definitive diagnosis, are typically available within a few days to two weeks. Based on the severity of the findings, the doctor recommends a schedule for the next screening. This may be ten years for a normal result or a shorter interval if precancerous polyps were discovered.