Anatomy and Mobilization of the Omentum

The omental flap has many uses in airway surgery. An omental flap based on a right gastroepiploic vascular pedicle is sufficiently long to reach any part of the airway. The omentum seems to possess unique abilities to enhance neovascularity, provide fibroplasia, and reestablish lymphatic drainage. Its bulk serves to fill space. It functions in the face of infection and helps to clear it. These functions have long been recognized.1,2 In 1988, Mathisen and colleagues described the uses of the omentum in the management of complicated cardiothoracic problems.3 This chapter deals only with its application to airway problems.

The greater omentum is supplied by branches from the right and left gastroepiploic arteries, which form variable arcades (Figure 42-1). Commonly, three major vessels branch more distally in the omentum to anastomose in inconstant vascular arcades.4 The right gastroepiploic artery is almost always of good caliber and with good flow, except if previously divided. The left gastroepiploic artery is smaller and less constant, especially in its anastomosis with the right gastroepiploic artery. The right artery extends well to the left of the midpoint of the greater curvature of the stomach. The pulse in the right gastroepiploic artery should always be palpated. Although 5 to 13 arteries to the omentum originate from the right gastroepiploic artery, only 1 usually continues from the left.2 It may or may not form an anastomotic arcade distally with other omental arteries. From the gastroepiploic arcade, multiple small branches flow to the greater curvature of the stomach. The short gastric arteries supply the greater curvature of the stomach above the left gastroepiploic artery. The veins parallel the arteries and empty into the portal system, most often via the superior mesenteric vein.

The omentum varies in length from 14 to 36 cm and in width from 23 to 46 cm.5 In a few patients, the omentum may be turned upward into the chest through an appropriate entry point without any mobilization. This is in effect an omentopexy. In most cases, it is necessary to detach the omentum from the transverse colon and also laterally from attachments to other abdominal structures. If the lesser omental sac is partially or completely obliterated, separation from the transverse mesocolon must be done with figure 42-1 Distribution of omental arteries and mobilization of the omentum. The gastroepiploic arcade is incomplete in about one-third of patients. The left gastroepiploic artery is inconstant in size and pattern. Distal epiploic arterial arcades are also extremely variable and may be incomplete. The superior dashed line indicates the line for omental mobilization with preservation of right gastroepiploic arterial supply. The lower dashed line represents the plane of separation of the omentum from the transverse colon. In many patients, this alone provides sufficient mobility for omental transfer.

Gastroepiploic Artery Origin

care to avoid injury to middle colic vessels. Detachment of the omentum from the transverse colon will provide sufficient length to reach nipple level in 75% of patients. The precise plane of dissection between the omentum and epiploic appendices of the colon is often unclear. The epiploic appendices should be left attached to the colon to minimize bleeding. The omental pedicle thus established often reaches the desired point in the thorax.

For further mobilization, I prefer to divide the left gastroepiploic artery and detach the gastroepiploic arch from the greater curvature of the stomach, carefully protecting the origin of the right gastroepiploic artery. The numerous short arteries to the stomach are individually ligated and divided one by one. With careful dissection, injury to the gastroepiploic arcade or to the stomach wall will not occur. When thus pedicled, the omentum will reach the base of the neck in 88% of patients. We have found that this degree of mobilization meets almost all the needs of the thoracic surgeon (Figure 42-2). A flap based on the left gastroepiploic artery is less dependable and provides little, if any, advantage. It is possible to obtain further length by dividing the arcade at one or more points to produce a longer pedicle.4,5 In such a case, atraumatic vascular clamps are placed at the points of the anticipated division of vascular arcades, and the distal omentum is examined for viability after about 10 minutes. Such division permits the omentum to reach as high as the skull, but there is an attendant risk of partial loss of blood supply.

Omental mobilization is most often done through an upper midline abdominal incision from the tip of the xiphoid to the umbilicus. The timing of omental mobilization and the route of transposition to the chest vary with the intended use. In treating the airway, there is no indication to transfer the omentum sub-

cutaneously. The routes for transposition of the omentum into the chest are most commonly a substernal tunnel immediately behind the retrosternal fascia or through incisions made through the diaphragm on either the right or left side anteriorly just beyond the costal attachments (Figure 42-3). Lateral incisions must be adequate to permit the omentum to pass through without compression of blood supply, and at the same time, snug enough to prevent herniation of intestine. A few sutures between the diaphragm and the omentum protect against herniation.

If a decision is made in advance to use the omentum in a patient who will be operated upon by thoracotomy, I prefer first to mobilize the omentum through a midline abdominal incision, with the patient supine, and place the omentum in a substernal tunnel or pocket that has been created. The abdominal incision is closed and the patient positioned for thoracotomy. Mobilization should therefore be generous, most often using a right gastroepiploic artery pedicle. At thoracotomy, the mediastinal pleura is opened, and the omentum is drawn into the hemithorax when needed. With cervicomediastinal approach to the trachea, a change of position is of course not required. If it is not clear whether the airway lesion is resectable prior to exploration by thoracotomy, the patient is placed in a modified thoracoabdominal position and the abdominal incision is deferred. In this case, transfer of the omentum to the chest may sometimes be more easily done through a small anterior diaphragmatic incision.

figure 42-3 Diaphragmatic apertures for transposition of omentum. A indicates the area of opening for substernal transfer. B and C indicate the regions of incisions for anterolateral passage.

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