The CT finding of thickened large intestine may denote following disease process;
1) Crohn's disease
2) Pseudo membranous colitis
3) Infectious colitis
4) Intramural (in between the walls) hemorrhage
5) Lupus vasculitis
6) Ischemic colitis.
Depending on the involvement of the bowel segment or generalized involvement, your gastroenterologist may contemplate a biopsy or further investigations.
Please feel free for your follow up questions.