Abdominal Wall Anatomy and Ostomy Sites

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Abdominal Wall Anatomy and Ostomy Sites

Jeremy M. Lipman

Introduction

Proper ostomy creation can significantly minimize the potential for associated morbidity. Incidents of peristomal hernia, pouch leak, skin complications, and bowel prolapse can all be reduced with an appropriately created ostomy.

Surgical Principles

The general location of the stoma will be determined by the type of ostomy required (proximal or distal bowel, small or large intestine) and by the reach of the mesentery associated with the bowel to be brought through the skin. Ideally, the patient should be examined preoperatively and potential ostomy sites marked by the surgeon or a trained enterostomal nurse. In cases in which the exact stoma location is unknown preoperatively, multiple acceptable locations may be marked to provide the surgeon with several options for placement. Markings are usually performed with permanent marker and may be scored with a needle intraoperatively to avoid removal during surgery.

The planned ostomy site should be placed over the rectus abdominis muscle whenever possible. Care should be taken to observe the patient standing, sitting, and reclining to identify and avoid skin creases and bony prominences that may cause pouching difficulties. Placement of the site should avoid the patient’s belt line and ensure easy visualization and reach by the patient, accounting for any functional limitations. Ideally, stomas should be located far enough from incisions to allow for placement of a stoma appliance lateral to existing or new incisions. By locating the stoma in the upper abdomen in obese patients, the surgeon may avoid placing the stoma through the pannus, decrease the amount of subcutaneous tissue between fascia and skin, and provide better visualization of the stoma for the patient.

Abdominal Wall Anatomy

The fasciae of the external and internal oblique and transversus abdominis muscles converge at the linea semilunaris, lateral to the rectus muscles (Fig. 20-1). Medially, these fasciae converge again at the linea alba. Superior to the linea semicircularis (arcuate line), usually at the umbilicus, the fasciae divide to encircle the rectus muscles completely, forming an anterior and a posterior rectus sheath. Inferior to the linea semicircularis, all layers of the fasciae are anterior to the rectus muscles, with only the transversalis fascia posterior.

FIGURE 20–1 Abdominal wall anatomy and rectus sheath.

Preoperative Imaging

Although no imaging is specifically required for ostomy creation, available imaging should be reviewed to avoid existing fascial defects during operation (Fig. 20-1, C).

External Landmarks

The ideal ostomy location is on the summit of the infraumbilical fat pad, within the boundaries of the rectus abdominis muscle (Fig. 20-2, A).

FIGURE 20–2 Ileostomy: anatomic landmarks and surgical technique.

Creating the Trephine

A circle of dermis is excised at the site of the planned ostomy; the subcutaneous tissues are not removed. When a midline incision has been made, the surgeon grasps the converged fasciae at the linea alba with a Kocher forceps through the skin incision. This forceps will be pulled medially to ensure the skin and muscular layers are aligned during creation of the trephine. Using a second Kocher forceps, the surgeon grasps the subcutaneous tissues at the planned ostomy site. A sponge is placed deep to the peritoneum through the incision and pushed anteriorly on the abdominal wall to protect the bowel and minimize the distance between abdominal wall layers (Fig. 20-2, B).

The subcutaneous fat is longitudinally divided with cautery through the fasciae of the anterior rectus sheath, exposing the rectus abdominis muscle. A clamp is placed between the fibers of the rectus muscle and is slowly spread transversely, separating the fibers without dividing them. The posterior sheath is then longitudinally divided with cautery onto the sponge pressing anteriorly against the peritoneum.

End Ostomy

Elevating the Bowel

The distal aspect of the divided small or large intestine is then oriented to ensure the mesentery has no twists or turns. A Babcock clamp is passed through the trephine and the intestine is brought through to the skin. No tension is applied, to prevent inadvertent damage to the intestines or mesentery (Fig. 20-3).

FIGURE 20–3 End colostomy.

Maturing the Ostomy

Several centimeters of bowel should be brought beyond the skin level. Sutures are placed full thickness from mucosa to serosa at the open end. The suture is then passed subcutaneously at the corresponding site on the trephine, taking care not to pass through the epidermis. Once sutures are placed in four quadrants, the bowel is everted while the sutures are tied (Fig. 20-4).

FIGURE 20–4 Brooke ileostomy technique.

Loop Ostomy

Elevating the Bowel

An appropriate segment of bowel is selected for the loop ostomy. Sutures of differing colors can be placed to mark the proximal and distal limbs to ensure correct orientation as the bowel is elevated. A window is created in the mesentery adjacent to the bowel, and umbilical tape is passed through the opening. The ends of the tape are then grasped through the trephine, elevating the ostomy above the skin. The umbilical tape is then exchanged for an ostomy rod (Fig. 20-5, step 1).

FIGURE 20–5 Loop-end ileostomy technique.

Maturing the Ostomy

The distal aspect of the loop is opened transversely across two-thirds its circumference, leaving the posterior wall intact. Distally, absorbable sutures are then placed (Fig. 20-5, step 2), with one in the center and one laterally just inferior to the rod on both sides. Sutures should be full thickness through the bowel and into the dermis, again taking care not to pass through the epidermis.

Sutures are placed proximally, in the same locations. While they are tied, the bowel is everted as a Brooke ileostomy. Brooke ileostomy allow for easier placement of the stoma appliance by elevating the stoma above the level of the epidermis (Fig. 20-5, steps 3 and 4).

Suggested Readings

Beck, DE. The ASCRS textbook of colon and rectal surgery. New York: Springer; 2011.

Corman, ML. Colon and rectal surgery. New York: Lippincott; 2004.

Gordon, PH. Principles and practice of surgery for the colon, rectum and anus. New York: Informa; 2007.

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