What is Crohn's disease primarily characterized by?

Crohn's disease is primarily characterized by the formation of granulomas in the intestinal walls. Granulomas are small clusters of immune cells that form in response to chronic inflammation, and their presence is a key pathological feature in Crohn's disease. This autoimmune condition can affect any part of the gastrointestinal tract but often involves the ileum and the colon. The formation of these granulomas indicates an inappropriate immune response, which is central to the disease’s underlying mechanism.

While other options describe various gastrointestinal issues, they do not capture the essence of Crohn's disease. Inflammation affecting the mucosal layer might relate more to conditions like ulcerative colitis, which is another form of inflammatory bowel disease but differs from Crohn's. Fluid accumulation in the peritoneal cavity indicates a different pathological process, possibly related to other conditions like ascites, and abnormally high blood pressure in the portal venous system is associated with liver disease, rather than Crohn's. Thus, the distinctive characteristic of granuloma formation is what primarily defines Crohn's disease.