The cecum marks the beginning of the colon and is a blind ending sac whose upper border is defined by the ileocecal valve. It is one of the widest portions of the colon. The word cecum comes from the Latin word “blind” since the proximal and inferior portion is blind ending. In herbivores it is fairly large since it is important in the digestion and fermentation of complex carbohydrates while it is small in carnivores who have little or no fiber in their diet.
It measures about 6 cm. in length and about 7.5cms in breadth and is situated in the right iliac fossa, usually above the inguinal ligament. Rapid cecal distention is a warning sign of an impending perforation. A cecal diameter >10 -12 cm is an ominous sign and may indicate impending perforation. However slow and chronic distension allows the cecum to adapt and hypertrophy its muscle so that larger diameters can be tolerated. It is therefore imperative to review old films before sending a patient off to the OR with a diagnosis of impending rupture.
Because of large capacity of the cecum, malignancy in the cecum rarely presents with obstruction. Thus patients who develop cecal carcinomas present relatively late in the disease usually presenting with a less dramatic anemia or occult blood in the stool. The importance of colonoscopic screening cannot be overemphasized. The U.S. Preventive Services Task Force strongly recommends that all men and women of 50years of age or older be screened for colorectal cancerusing one of the following techniques: fecal occult blood testing each year, flexible sigmoidoscopy every five years, fecal occult blood testing every year combined with flexible sigmoidoscopy every five years, double-contrast barium enema every five to 10 years or colonoscopy every 10 years.
The cecum is usually covered by peritoneum on less than two thirds of its circumference making it a fixed retroperitoneal structure, but in about 5-10 % of people it is devoid of peritoneal fixation and is associated with an elongated mesentery making the cecum and proximal part of the ascending colon unusually mobile.
The cecum is supplied by the ileocolic artery which is a branch of the SMA and its venous drainage is into the SMV.
The floppy cecum and ascending colon are given the freedom to rotate which predisposes the structure to two types of important mechanical diseases. When it flops and kinks anteriorly and upward the resulting entity is called cecal bascule – usually a reversible kink. The word bascule comes from the French word drawbridge n a structure that raises up on one side and is hinged at its base which acts as a fixed point. In cecal bascule the fixed point is in the ascending colon while the floppy cecum moves on the hinge, flips upward to the right upper quadrant and kinks the bowel. This flip often reverses itself. The clinical presentation is one of intermittent obstruction and pain which commonly subsides as the kink spontaneously reverses itself. The radiographic appearance is one of a dilated cecum that is located in the RUQ in a subhepatic location.
When the bowel twists around itself, torsion or volvulus occurs along the longitudinal axis of the ascending colon with a twist of 180-360 degrees it usually cannot untwist itself easily and the resulting volvulus is complicated by vascular compromise, infarction of the bowel wall and perforation – a condition with high mortality. The radiographic image is usually characteristic with the dilated loop, sometimes described as an omega shape, presenting as dilated loop in the left upper quadrant with a twisted or whirl like appearance. A barium enema would give a beak shaped appearance at the site of the twisting in the right lower quadrant. Either way when the colon reaches 12cms it implies impending rupture. A 9cms cecum in the appropriate clinical setting, particularly if rapid distension is the presentation, should raise concern for rupture.
An inverted cone best describes the normal shape of the cecum with the point of the cone pointing down, while the slit like ileocecal junction situated medially further defines its characteristic shape. The three longitudinal taenia described above originate near the base of the appendix and further define the shape of the cecum and depending on their positioning as well as their state of contraction the cecal shape will be defined at any given time. There are a number of conditions that cause the cecum to become narrowed, spastic, or coned caused by intrinsic disease of the cecum, muscle spasm within the cecum, or mass effect on the cecum by extrinsic disease. These diseases include infections such as amebiasis, TB, actinomycosis, typhoid fever, typhlitis, and appendicitis and inflammatory diseases such as Crohn’s disease, and ulcerative colitis. Carcinoma and mucocele of the appendix are other entities that can deform the cecum.
Acute appendicitis often deforms the cecum. The cecum is described as an arrowhead sign since the base of the appendix squeezes the cecum from the outside and the crescentic effect leads to a shape reminiscent of an arrowhead.
There are a few entities that you may come across that are unique to the cecum including a condition called typhlitis. This disease of the cecum is characterized by a severe inflammation in patients with leukemia and other white cell dyscrasias whose white cell count is less than less than 1000/microL, and who are usually in the midst of chemotherapy. The exact cause is not known but presumed to be multifactorial. (eMedicine)
Another condition commonly seen in the cecum is intussusception. (eMedicine) In children it is usually a benign entity that can often be treated with a gentle barium enema, while in adults it is usually associated with a tumor acting as the leading edge and has the additional risk of ischemic or obstructive complications. In the adult, surgery is indicated once the diagnosis is made. The findings are characterized by the finding of bowel within bowel, so that in the centre one should see a narrow column of contrast in the inner lumen of the intussusceptum, surrounded by some mesenteric fat that has been dragged into the receiving loop, and then a hint of coiled springs of mucosa that has been telescoped by the process, and lastly the loop of receiving bowel called the intussuscipiens. Ischemic or obstructive changes may be associated.