A colonoscopy is a medical procedure allowing a doctor to examine the entire inner lining of the large intestine, or colon, using a flexible tube with a camera. During this visual assessment, a biopsy is the removal of a small piece of tissue for laboratory analysis. This practice is employed whenever visual findings alone are not enough to establish a definitive diagnosis. The microscopic examination of the tissue sample is required to confirm or rule out a potential disease process.
Investigating Polyps and Potential Cancer
The primary reason a biopsy is taken during a routine colonoscopy is for the assessment of suspicious growths, most commonly polyps. While a doctor can see a polyp and remove it completely during the procedure, only a microscopic analysis can determine the nature of the cells within that growth. This examination is the only way to differentiate between a non-concerning benign growth and a potentially precancerous or cancerous one.
Polyps are broadly classified into non-neoplastic, such as hyperplastic polyps, and neoplastic polyps, which can progress to cancer over time. The neoplastic group includes adenomatous polyps and sessile serrated lesions. Biopsies confirm the exact type of polyp and the degree of dysplasia, or abnormal cell development, present in the tissue.
If a polyp is small enough, the entire growth is removed during the procedure. The entire specimen is then sent to the lab for analysis to ensure the margins are clear and to confirm the polyp type. If a mass is too large or appears highly suspicious of advanced cancer, the doctor may take only a small tissue sample, or biopsy, rather than attempting a complete removal.
The pathologist’s report on these samples is fundamental for determining a patient’s future surveillance schedule. The discovery of advanced adenomas places a patient at a significantly higher long-term risk for developing colorectal cancer. Identifying these precancerous lesions and confirming their cellular characteristics allows physicians to recommend an accelerated schedule for repeat colonoscopies.
Confirming Inflammatory Bowel Disease and Colitis
Biopsies are also frequently obtained from areas that show signs of inflammation, ulceration, or mucosal changes. Visual signs of redness or friability in the colon lining are suggestive but not diagnostic of a specific disease. The tissue samples are required to distinguish between different types of colitis.
This microscopic distinction is particularly important for diagnosing Inflammatory Bowel Disease (IBD), which includes Ulcerative Colitis (UC) and Crohn’s Disease (CD). While both conditions cause inflammation, the pattern and depth of inflammation seen in the biopsy help differentiate between them. UC typically presents with inflammation confined to the superficial mucosal layer.
In contrast, Crohn’s Disease often involves patchy, segmental inflammation that can affect the full thickness of the bowel wall, and it may include features like granulomas. Biopsies are also necessary to rule out other forms of inflammation, such as infectious colitis or microscopic colitis. In cases of microscopic colitis, the diagnosis is made entirely by the presence of specific inflammatory cells seen only under the microscope.
To ensure an accurate diagnosis, multiple tissue samples are often taken from different sites, including both areas that look inflamed and areas that appear healthy. Analyzing these samples allows the pathologist to map the distribution and specific cellular characteristics of the inflammation. This pathological confirmation is a prerequisite for establishing the correct long-term treatment plan, as UC and CD are managed with different medications and surgical considerations.
The Journey of the Sample: What Pathology Reveals
Once the small tissue sample is collected during the colonoscopy, its journey to a definitive diagnosis begins immediately in the pathology laboratory. The sample is quickly placed into a container filled with a fixative solution, which preserves the cellular structure and prevents the tissue from degrading.
In the lab, the preserved tissue is processed by being embedded in a block of paraffin wax, which provides a firm structure. A specialized instrument called a microtome is then used to cut the wax block into extremely thin slices. These slices are placed onto glass slides and stained with dyes, most notably Hematoxylin and Eosin (H&E), which color the cell nuclei blue and the surrounding cytoplasm pink.
The stained slides are then examined by a pathologist. The pathologist studies the cellular architecture, looking for abnormal cell shapes, patterns of growth, or infiltration by inflammatory cells. This microscopic review translates the visual findings from the colonoscopy into a specific medical conclusion, such as a benign hyperplastic polyp, a precancerous adenoma, or evidence of chronic inflammation.
The final pathology report provides the definitive diagnosis, which is used by the gastroenterologist to determine the appropriate follow-up and treatment plan. This plan may involve surgical removal, medication, or a specific surveillance schedule.