Mesenteric injury occurs in 18 per cent of patients with penetrating abdominal injury and 5 per cent of those with blunt abdominal trauma. The latter figure has been substantiated by a recent review which reported 41 major mesenteric injuries in a population of 870 patients undergoing laparotomy for blunt abdominal trauma (4.7 per cent). Thirty-four patients had injury to the small bowel mesentery; 10 of these injuries involved the root, with disruption of either the superior mesenteric artery or vein. The colonic mesentery was damaged in seven patients and six of these injuries were in the right colon.

Mesenteric injury in blunt trauma arises from a shearing force (see Fig. 3 1348, Section 26.1). In experimental animals the injury can be reproduced by compression between two opposing surfaces such as the abdominal wall and spine. In this animal model the site of injury cannot be related to the intraluminal pressure, the fixation of the bowel at the ligament of Treitz, or the presence or absence of air and fluid within the intestine. Such shearing forces can be generated not only by the traumatic incident itself but also by protective devices such as car safety belts during a sudden deceleration, especially if these are worn across the abdomen rather than across the bony pelvis. Experimentally, more severe intra-abdominal injuries are associated with higher abdominal compression loads.

Mesenteric injury is seldom diagnosed preoperatively: the injury tends to be found at exploratory laparotomy. The preoperative diagnosis of haemoperitoneum may be made from clinical findings, diagnostic peritoneal lavage, CT scan, or ultrasound and, in the adult population, this is an indication for surgical exploration. The patient with a bleeding mesenteric laceration has a clinical presentation of blood loss, hypotension, abdominal tenderness, a falling haematocrit, and abdominal distension. If pain is prominent, intestinal ischaemia should be suspected. It is the policy of the Massachusetts General Hospital that all penetrating gunshot wounds of the abdomen are explored; penetrating wounds from knives or similar objects entering the abdominal cavity are also explored, although some institutions advocate a selective approach.

All patients undergoing abdominal exploration for trauma require inspection of the entire length of the intestine as an integral part of operative management; a search should be made for mesenteric haematomas, tears in the mesentery and ischaemic bowel.

Non-expanding haematomas and contusions of the mesentery should not be explored if the bowel is definitely viable. If a haematoma of the mesentery is expanding, proximal and distal control should be obtained and the haematoma explored. The management of injury to major intestinal vessels is out of the scope of this chapter.

If the haematoma appears to compromise intestinal viability, the surgeon needs to decide between resection and expectant observation; in the large bowel, exteriorization of the compromised section is an additional option. Intraoperative Doppler examination or intravascular injection of fluorescein may assist the surgeon in these difficult cases. A ‘second look’ should be considered, close re-examination of the bowel being performed within 24 h of the original laparotomy.

If a laceration is actively bleeding, haemostasis should be obtained with artery forceps, after which sutures can be placed to preserve haemostasis, taking care not to compromise distal circulation and so avoiding intestinal ischaemia. Once haemostasis is obtained, the mesenteric defect should be closed using interrupted absorbable sutures. The defect may require both anterior and posterior surfaces to be closed, especially if the mesentery is thick, as in an obese patient. At the termination of the procedure, the viability of the bowel should be confirmed and noted in the operative record.

Following blunt trauma the mesenteric laceration may parallel the bowel and disrupt the arterial arcade, so that the surgeon at laparotomy will be presented with a bleeding mesentery and a section of ischaemic bowel, usually small intestine. In these patients there is no choice but to perform a bowel resection. After obtaining haemostasis, small bowel resection can be performed in one or two layers or with the use of a stapler. Once bowel continuity is restored, the surgeon should repair the mesenteric defect. The surgeon's options for treating ischaemic colon include resection with primary anastomosis, resection with colostomy (or ileostomy for an ischaemic right colon), mucus fistula, or Hartmann's pouch. If there is uncertainty, a segment of ischaemic colon can be exteriorized.

If there is a mesenteric injury and ischaemic bowel from a penetrating injury, the decision as to whether revascularization is to be attempted should be made soon after opening the abdomen. Issues such as the length of time that the bowel has been ischaemic, the mechanism of injury, the extent of other injuries, the length of bowel involved, and the likelihood of successful revascularization need to be considered.

Complications following the repair of injured mesentery include bleeding, bowel ischaemia, and bowel obstruction. Bowel obstruction can arise from both adhesions or an internal hernia through a patent mesenteric defect. Continuing blood loss following laparotomy requires re-exploration to be performed. If there is concern over bowel viability, the patient should be re-explored within 24 h of initial surgery. A mesenteric defect that is either missed at laparotomy or inadequately repaired can serve as the site of an internal hernia with potentially fatal consequences; death may occur from septicaemia from a portion of gangrenous intestine.

Mesenteric injury is common in both penetrating and blunt abdominal trauma. Although not often diagnosed preoperatively, surgeons should evaluate the mesentery as part of the trauma laparotomy; if appropriately managed, a cause of morbidity and even mortality may be avoided.

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