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Anatomy and Physiology

The large bowel starts at the cecum, moves up to the ascending colon with the hepatic flexure, the transverse colon with the splenic flexure, the descending colon, and the sigmoid colon. As the content moves through the colon, it gets firmer in consistency as a result of water and electrolyte absorption in the large bowel.

The most common type of colostomy is the sigmoid colostomy followed by the transverse colostomy, while ascending and descending colostomies are rare and hardly performed.

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There are different types of colostomies, including loop colostomy, double-barrel colostomy, and end colostomy. The different types of colostomies are created depending on the indication, length of the mesocolon, and amount of diseased and remaining normal bowel.

The content of effluent in the different types of colostomies varies from soft and loose, foul-smelling, oatmeal-like stool in the ascending and transverse colostomies to firmer, paste-like stool from the transverse and descending colostomies, to output resembling normal stool from a sigmoid colostomy. As the stool gets firmer along the colon, the output becomes easier to manage.

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Colostomies are generally made in the anterior abdominal wall over the rectus abdominis muscle to either side of the linea alba, generally inferior to the umbilicus. Occasionally the site is cephalad to the umbilicus, particularly in obese patients, as the anterior abdominal wall has less subcutaneous fat in the upper part. During the procedure, a circular incision is created over the pre-identified stoma site. It needs a flat surface on the abdomen of at least 2 to 3 inches and should be away from the beltline, any scars, as well as bony prominences to ensure a secure seal of the stoma appliance. The incision is deepened onto the anterior rectus sheath, which is incised in a cruciate fashion.

The rectus muscle is retracted sideways, without cutting into the muscle itself, and the posterior rectus sheath is again incised in a cruciate manner. The loop of bowel that is identified for the stoma creation is pulled through the incision and exteriorized onto the skin. The identification of the bowel is aided by performing a diagnostic laparoscopy to ensure good mobility and reach the anterior abdominal wall without tension. However, the stoma can also be created in a trephine manner without a laparoscopic approach. It is important to consult cross-sectional imaging to pre-identify the most mobile segment of the bowel and mark the colostomy site in accordance. A transverse colostomy should be fashioned in the left upper quadrant, a sigmoid colostomy in the left iliac fossa.

Once it is exteriorized, a stoma rod can be eased through the mesocolon to reduce the risk of retraction into the abdominal cavity. The colon is incised three-quarters of the circumference and the bowel edges fixed to the skin with interrupted sutures using an absorbable suture material and raising the stoma above the skin level slightly. In contrast to an ileostomy, colostomies generally do not require eversion and 3-point fixation, owing to the content having less enzymatic action.[1]

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