Which of the following is NOT true when comparing Crohn's disease to Ulcerative colitis?

Ulcerative colitis is characterized by continuous inflammation that typically starts in the rectum and can extend proximally in a continuous manner through the colon. "Rectal sparing" implies that the rectum is not involved in the disease process, which is not true for ulcerative colitis. In fact, the rectum is often affected, and the disease usually begins there.

The correct answer highlights this distinction and underscores the fundamental pathophysiological differences between Crohn's disease and ulcerative colitis. While Crohn's disease may involve areas of the gastrointestinal tract discontinuously (leading to the appearance of "skip lesions") and can produce various complications such as fistulas and "cobblestone" appearances due to transmural inflammation, ulcerative colitis is different in that it typically has a continuous pattern of disease involvement and usually does not spare the rectum.

In this context, it's essential to understand that the patterns of disease manifestation and inflammation in these two conditions are key elements in their diagnosis and management.