Colorectal carcinomas are the most common gastrointestinal tract tumors. 50-60% of colorectal carcinomas originate in rectum and sigmoid colon. Colorectal carcinoma is a frequent disease. New and improved surgical techniques and the implementation of adjuvant and neoadjuvant therapy have improved the 5 year survival rate significantly. Accurate preoperative assessment of tumor extent is essential for choosing the appropriate therapeutic strategy, and thus for patient prognosis.