A colonoscopy allows a doctor to visually examine the entire large intestine (colon and rectum) using a long, flexible tube equipped with a camera. This examination is frequently performed for cancer screening or to investigate symptoms such as chronic diarrhea or unexplained bleeding. During the procedure, the physician may perform a biopsy, removing a small piece of tissue using tiny instruments passed through the scope. This tissue specimen is analyzed in a laboratory, providing a microscopic view of the cells that is not possible through visual inspection alone.
The Purpose of Tissue Sampling
Tissue sampling during a colonoscopy serves two distinct purposes: to remove abnormal growths and to diagnose underlying mucosal diseases. The most common reason for a biopsy is to remove a polyp, which is an abnormal growth of tissue that can develop into cancer over time. When a polyp is found, the goal is often to remove the entire lesion, a process called polypectomy, preventing potential future malignancy.
The second primary purpose is diagnostic, often involving areas that appear inflamed or even completely normal. Physicians take samples to look for microscopic evidence of disease when a patient has symptoms like persistent diarrhea. This method is used to diagnose conditions such as Inflammatory Bowel Disease (IBD), including Crohn’s disease and ulcerative colitis, or microscopic colitis, where the colon lining only shows abnormalities under a microscope. These biopsies help determine the cause of symptoms and guide appropriate medical treatment.
Factors Influencing the Number of Samples Taken
The number of biopsies taken during a colonoscopy is not fixed and varies significantly based on the findings and the specific reason for the procedure. If the colonoscopy is purely a screening examination and no polyps or suspicious areas are found, zero biopsies may be taken. Conversely, the number of samples can range from a single specimen to dozens, depending on the clinical scenario.
When polyps are discovered, the number of specimens is directly related to the number and size of the growths removed. For example, if a physician removes five separate polyps, this will result in five distinct specimens. A single, larger polyp may also be removed in multiple fragments, which are collected together and placed into a single container for the pathologist to examine as one specimen.
For diagnostic purposes, such as investigating potential microscopic colitis, a systematic sampling protocol is followed to ensure adequate tissue representation. A common protocol involves taking multiple random biopsies, often six to eight total, from different segments of the colon, such as the ascending, transverse, and descending colon. This is done because the pathological changes for microscopic colitis can be patchy and are not always uniform throughout the entire length of the large intestine.
In cases of long-standing Inflammatory Bowel Disease, particularly for cancer surveillance, the number of biopsies can be high. Historically, some surveillance protocols required taking multiple biopsies, sometimes exceeding 30 specimens, from four quadrants every ten centimeters throughout the colon. While advanced imaging techniques now allow for more targeted sampling of suspicious areas, a physician may still take numerous random biopsies in addition to targeted ones, especially if the patient has a complex medical history or other risk factors.
Processing and Analysis of Biopsy Samples
Once the tissue samples are collected, they are immediately placed into small, labeled containers filled with a chemical fixative. This fixative preserves the cellular structure and prevents the tissue from degrading before it reaches the pathology laboratory. Each container is labeled to indicate the patient and the exact anatomical location within the colon where the sample was taken.
Upon arrival at the pathology lab, the tissue specimens undergo a detailed process orchestrated by a pathologist. First, the samples are examined with the naked eye (gross examination), where the pathologist notes the color, size, and texture. The specimens are then processed by dehydrating them and embedding them in a block of paraffin wax, which provides a stable medium for extremely thin slicing.
These thin slices are placed onto glass slides and stained with special dyes to make the cellular components visible. The pathologist then examines the stained slides under a microscope, looking for abnormalities such as inflammation, cellular changes like dysplasia (pre-cancer), or invasive cancer. This analysis is necessary to determine the exact nature of the tissue.
The final step is the creation of a pathology report, which is sent to the referring physician. This report confirms the number of specimens received and provides a formal diagnosis for each sample, including the specific type of polyp or the severity of any inflammatory condition. The typical turnaround time for receiving the final biopsy results is often between five and ten business days, depending on the laboratory’s workload and the need for specialized staining.