A well-defined fat plane is demonstrated between the posterior wall of the bladder and the mass located near the vault of the vagina. Colorectal cancer is the third most common cause of cancer death in the United States. It appears to be associated with diets high in animal fat and protein and low in fiber. Seventy percent of colorectal cancers occur in the rectosigmoid region. Rectal cancers may present with bleeding, change in bowel habits, perineal pain, and symptoms of invasion of adjacent organs including hematuria, urinary frequency, or vaginal fistulas.
Surgical removal is the only effective therapy.
Anterior resection with anastomosis to the rectal stump is performed for upper rectal tumors and a combined abdominal and perineal resection with a permanent colostomy for distal rectal lesions. On CT, rectal lesions may appear as focal lobulated soft tissue masses with asymmetrical or circumferential thickening of the bowel wall. Narrowing of the lumen and bowel obstruction may be evident. Extension into pericolonic fat or adjacent structures, regional adenopathy, adrenal or liver metastases, and hydronephrosis may also be visualized. Common sites of local extension include the pelvic musculature, bladder, prostate, ovaries, and seminal vesicles.