Crohn’s disease is a type of Inflammatory Bowel Disease (IBD) that causes chronic inflammation anywhere along the digestive tract, from the mouth to the anus. The inflammation in Crohn’s disease often affects the lower part of the small intestine and the large intestine. A colonoscopy is a medical procedure where a gastroenterologist uses a long, flexible tube with a camera, called a colonoscope, to visually examine the lining of the rectum and colon. This procedure is typically performed under sedation, and it provides a direct, detailed view of the lower gastrointestinal tract.
The Primary Role of Colonoscopy in Diagnosis
A colonoscopy is considered a foundational tool for detecting and diagnosing Crohn’s disease. The procedure allows for the direct visualization of the inner lining, or mucosa, of the large intestine and the final segment of the small intestine. This ability to physically see the state of the intestinal tissue makes it highly valuable compared to indirect imaging methods.
The scope’s capability to reach the terminal ileum, the last part of the small intestine before it connects to the large intestine, is particularly important for Crohn’s detection. This segment is one of the most common locations for the disease to manifest. Visualization also helps determine the extent and distribution of inflammation within the lower digestive tract. Physicians can precisely map affected sections, which is necessary for classifying the disease and guiding treatment. The procedure is also essential for differentiating Crohn’s disease from Ulcerative Colitis (UC), the other main type of IBD.
Visual Markers of Crohn’s Disease
During the colonoscopy, the physician looks for specific visual characteristics highly suggestive of Crohn’s disease. One distinctive feature is the presence of “skip lesions,” which are patches of inflamed tissue separated by sections of healthy, unaffected tissue. This patchy pattern is a strong indicator of Crohn’s, as other forms of colitis usually involve continuous inflammation.
Another common visual sign is the “cobblestoning” appearance of the mucosa. This texture is caused by deep, linear ulcerations that separate raised, swollen areas of less-affected mucosa. The raised areas resemble the rounded stones in a cobblestone street, giving the condition its name. The ulcerations in Crohn’s tend to be deep and longitudinal, sometimes described as fissures. These deep sores differ from the typically superficial inflammation seen in other forms of IBD.
Confirmation Through Biopsy and Histology
While visual findings strongly suggest Crohn’s disease, a definitive diagnosis requires collecting small tissue samples, known as biopsies, during the colonoscopy. These samples are sent to a pathology laboratory for histology, the microscopic analysis of the tissue’s cellular structure. The biopsy process is painless and allows the medical team to confirm the nature of the inflammation seen.
Pathologists examine the samples for evidence of chronic inflammation and architectural distortion, which are hallmarks of IBD. The presence of non-caseating granulomas is a highly specific finding for Crohn’s disease. Granulomas are collections of inflammatory cells that appear walled-off, and their detection is a strong piece of evidence, although they are only found in about 35% of cases. Histology also helps distinguish Crohn’s disease from Ulcerative Colitis, as Crohn’s is characterized by transmural inflammation, affecting the entire thickness of the bowel wall, whereas UC typically only affects the innermost lining.
Integrating Additional Diagnostic Tests
A colonoscopy is limited because it only views the large intestine and the terminal ileum, leaving the rest of the small intestine and the upper GI tract unexamined. Since Crohn’s disease can affect any part of the digestive system, other tests are necessary to determine the full extent of the condition. These supplementary diagnostic tools provide a complete picture of the disease’s location and severity.
Imaging tests are frequently used to visualize the small bowel, which is inaccessible to a standard colonoscope. Magnetic Resonance Enterography (MRE) or Computed Tomography Enterography (CTE) are common options that use contrast material to provide detailed cross-sectional images of the small intestine. These scans detect inflammation, narrowing of the bowel (strictures), and abnormal connections (fistulas) often associated with Crohn’s.
Capsule endoscopy involves the patient swallowing a pill-sized camera that takes thousands of pictures as it travels through the small intestine, capturing images that MRE or CTE might miss. Laboratory tests on blood and stool samples provide non-visual indicators of inflammation. Elevated levels of C-reactive protein (CRP) in the blood or fecal calprotectin in the stool suggest active inflammation in the body and gut, supporting the diagnosis and helping to monitor disease activity.