Normal ileocecal junction
The ileocecal junction marks the transition from the small bowel to the large bowel.
Although the portal has traditionally been termed the "ileocecal valve", anatomic studies suggest that it is more of a sphincter than a valve (in the mechanical sense of the mitral "valve") 1,2,3.
Any pathologic process that affects the cecum or the paracaecal area (e.g. the paracaecal mesenteries) may disrupt the sphincter. Carcinoma can arise off the valve, infections of the ileocecal junction (e.g. tuberculosis) can affects its function, and inflammatory bowel disease (e.g. ulcerative colitis) can stricture the valve, leading to backwash ileitis from the colon. A carcinoid tumor in the right lower quadrant mesenteries could tether the ileocecal junction and disrupt the sphincter's function.
The fat attenuation at the ileocecal junction also serves as a landmark for finding the appendix... the appendix is always below it.