Ulcerative Colitis (UC) is a chronic inflammatory bowel disease (IBD) that causes inflammation and ulcers in the lining of the large intestine, known as the colon. While symptoms and imaging can suggest UC, a biopsy remains the definitive procedure for establishing a diagnosis. This test involves examining tissue samples under a microscope to reveal the characteristic cellular changes. The findings confirm the presence of UC and guide treatment decisions and long-term monitoring strategies.
Why Biopsies are Essential for UC Diagnosis and Management
A biopsy provides microscopic evidence of disease activity that is not visible during a visual examination. While a colonoscopy can reveal the gross appearance of inflammation, ulceration, and bleeding, only the tissue analysis can provide a definitive diagnosis. This microscopic confirmation is necessary to distinguish UC from other conditions that cause similar symptoms, such as infectious colitis or other forms of IBD.
The biopsy helps differentiate UC from Crohn’s Disease, which often requires a different management approach. The pathologist looks for distinct patterns of inflammation and tissue damage to accurately classify the type of bowel disease. Biopsies are also used after diagnosis to assess how well a patient is responding to treatment by determining the level of active inflammation remaining in the tissue. Achieving microscopic healing, or mucosal remission, is confirmed only by a biopsy.
The Process of Tissue Sample Collection
Tissue collection occurs during an endoscopic procedure, typically a colonoscopy or a flexible sigmoidoscopy. The gastroenterologist uses a long, flexible tube equipped with a camera to visualize the inner lining of the colon. Tiny forceps passed through the endoscope are then used to pinch off small pieces of the mucosal lining.
The procedure involves systematic sampling, often referred to as pancolonic sampling, where tissue is collected from multiple, distinct locations throughout the entire colon. This comprehensive approach is necessary because UC can affect the colon continuously, and taking samples from both visibly inflamed and seemingly normal areas helps determine the full extent of the disease. Samples may also be taken from the terminal ileum to help rule out Crohn’s Disease. Immediately after collection, the delicate tissue samples are placed into a preservative solution, typically formalin, which stabilizes the cells for processing at the pathology laboratory.
Analyzing the Pathological Features of Ulcerative Colitis
Once the tissue reaches the lab, a pathologist prepares the samples on slides to be examined under a microscope. The pathologist looks for a combination of chronic and active inflammatory features. Chronic changes include a distortion of the crypt architecture, which are the small glandular structures in the colon lining.
In UC, these crypts often appear shortened, branched, or irregular, a sign of repeated cycles of injury and repair over time. A specific chronic feature is basal plasmacytosis, which is an unusually dense collection of plasma cells gathered at the base of the crypts near the muscle layer of the mucosa. Active inflammation is characterized by the presence of neutrophils in the glandular structures.
When neutrophils accumulate within the crypts, they form what are called crypt abscesses, a classic finding in active UC. The inflammation in UC is generally confined to the mucosal layer, which is the innermost lining, unlike Crohn’s Disease, which typically involves deeper layers of the bowel wall. The pathologist grades the severity of the colitis based on the density of inflammatory cells, the extent of architectural distortion, and the presence of active features like crypt abscesses.
Biopsy Surveillance for Dysplasia and Long-Term Monitoring
Beyond the initial diagnosis, biopsies play a role in the long-term surveillance of UC patients. Individuals who have had extensive UC for many years face an elevated risk of developing colorectal cancer. This risk increases with the duration and extent of the colitis.
The long-term surveillance aims to detect dysplasia, pre-cancerous cellular changes in the colon lining. Patients with long-standing or extensive disease begin regular surveillance colonoscopies, often starting eight to ten years after their initial diagnosis. During these procedures, the clinician takes multiple biopsies, sometimes utilizing advanced imaging techniques like chromoendoscopy to highlight subtle changes in the mucosa.
The pathologist classifies any detected dysplasia as either low-grade or high-grade, which significantly impacts the patient’s management plan. Low-grade dysplasia may require more frequent monitoring and follow-up colonoscopies. The presence of high-grade dysplasia often suggests a higher risk of developing cancer and may lead to discussions about surgical removal of the colon to prevent the progression to invasive cancer.