Which of the following best describes the routes of inflammation in Crohn's disease?

In Crohn's disease, the inflammatory process is characterized as transmural, meaning it affects all layers of the bowel wall, including the mucosa, submucosa, muscularis propria, and serosa. This extensive involvement can lead to complications such as strictures, fistulas, and abscess formation, which are common in Crohn's disease due to the full thickness inflammation. The distinction between Crohn's disease and other types of inflammatory bowel disease, such as ulcerative colitis, is important here. In ulcerative colitis, for instance, inflammation is typically limited to the superficial layers of the bowel wall, primarily affecting the mucosa and submucosa.

The option suggesting that inflammation is restricted to superficial layers does not accurately reflect the nature of Crohn's disease. Additionally, stating that only the rectum is involved is misleading, as Crohn's disease can affect any part of the gastrointestinal tract from the mouth to the anus, but it does not typically do so in a confined manner. Therefore, the most precise description of the inflammatory routes in Crohn's disease is that it involves the entire thickness of the bowel wall, which is reflected in the correct choice.