Traumatic abdominal wall hernia (TAWH) is defined as disruption of the abdominal wall musculature and fascia with herniation of intra-abdominal contents, in the absence of surgery to that area of the abdominal wall.^[1] It is rare, with an incidence of 0.17%-0.90% in patients with blunt abdominal trauma.^[2,3] Deceleration forces caused by falls from height or seat belt injuries are the most common causes of TAWH.^[4] Low-energy blunt injuries from bicycle or motorcycles handlebars or charging animals are less frequent causes. Due to the rare incidence and complex presentation of this condition with other distracting injuries, this diagnosis is often not considered, resulting in missed or delayed diagnosis. We present a case of a 46-year-old male who suffered major abdominal trauma, and was found to have TAWH as well as intra-abdominal organ injury.

A 46-year-old male patient presented to the emergency department (ED) after being involved in a high-speed motor vehicle accident. His car rolled over and he was entrapped upside down for 30 min, with the lap seat belt cutting across his lower abdomen during that time. He was extricated by emergency medical services, and was transforted by helicopter to the ED. He complained of pain over the chest, pelvis and right knee. He also complained of bleeding around the right eye. He denied shortness of breath or loss of consciousness, and was able to move all his limbs. On arrival, his heart rate was 128 beats/min, respiratory rate was 30 breaths/min, blood pressure was 120/70 mmHg (1 mmHg=0.133 kPa) and oxygen saturation was 98% on 6 litres of oxygen. His Glasgow Come Scale (GCS) was 14 (E3 V5 M6). His height was 185 cm and weighed 116 kg. Clinical examination revealed an intact airway, but there was tenderness bilaterally over the chest wall on palpation and a slight reduction in air entry over the left lung. There was no cephalhematoma or tenderness over the cervical spine. There was contusion over his upper lip, right orbit and right cheek and superficial laceration over the right eyelid. His pupils were bilaterally equal and reactive to light with normal visual acuity. There was abrasion over the lower abdomen but no obvious tenderness. There was no bruising around the flank. Examination also revealed deformity over the right knee, but there was no external hemorrhage and the distal pulsations and sensations of the lower limb were normal. Pelvic binder was applied in view of suspicion of pelvic injury. The patient was log-rolled, there was no spinal step or deformity and his anal tone was normal.

The initial laboratory tests including hemoglobin, creatinine, liver function test and coagulation profile, were normal. Bedside ultrasound did not show hemoperitoneum or hemopericardium. Computed tomography (CT) scans of the head and cervical spine were normal. A CT scan of the chest showed bilateral rib fractures with flail segments of the left 9^th to 11^th ribs, left scapular fracture, bilateral pulmonary contusion, small right hemo-pneumothorax and small left hemothorax. A CT scan of the abdomen and pelvis indicated a 6-cm left lateral abdominal wall defect with herniation of multiple loops of small bowel (Figure 1), but there was no obvious suggestion of perforation. X-ray of the right knee showed widening of the lateral compartment and tiny intercondylar fragments suggestive of lateral and cruciate ligament injury. There was no indication of chest tube insertion for small hemopneumothorax and a decision was made to monitor the patient as an inpatient.

In view of traumatic abdominal wall hernia, the decision was made by the trauma team to transfer the patient to the operating room (OR) from the ED. He underwent an exploratory abdominal laparotomy, which showed a large amount of bowel herniation in the subcutaneous space through the full thickness defect in the abdominal muscles extending from the lateral border of the rectus abdominis muscle towards the quadratus lumborum and the psoas muscle posteriorly. There was some blood in the peritoneal cavity, mesenteric contusion in the ileocolic region, contusion over the posterior aspect of the cecum with a 3-cm serosal rent up to the sub-mucosa and complete rent in the mesentery of the apex of the sigmoid colon with impending perforation. He underwent a sigmoid colectomy with over-sewing of caecal serosal tears. A 25 cm × 20 cm Bio-A mesh was anchored onto the quadratus lumborum muscle posteriorly and each individual muscle layer including the transversus abdominis, external oblique and internal oblique muscles, was closed in layers. Two drains were placed, one in the retromuscular space overlying the mesh and the other in the subcutaneous space. Orthopedic surgeons examined his right knee in the operating theatre and found lateral collateral and posterior cruciate ligament injury. They applied a Zimmer knee splint and planned to perform magnetic resonance imaging (MRI) of the right knee prior to performing surgical repair. He was then admitted to a high dependency unit under trauma service for subsequent care. He was started on intravenous antibiotics (cefuroxime, metronidazole and gentamycin). A few days later, the patient was noted to be hypotensive with a blood pressure of 85/62 mmHg; hence, in view of the consideration of intra-abdominal sepsis, he was taken to the OR and was noted to have multiple serosal tears on the dilated large bowel from the ascending colon to the site of the sigmoid anastomosis which had necrosed. This leads to fecal contamination on the left side of the abdomen, which extendeds into this hernia repair. The fecal contamination was washed and the patient underwent a staged ileostomy the next day. He had been stable post-operatively. His scapular fracture was managed conservatively. Subsequent MRI of the right knee showed complete rupture of the anterior and posterior cruciate ligaments, complex medial meniscus tear, severe lateral ligamentous complex/posterolateral corner injury, medial tibial spine fracture, medial femoral compartment impaction fracture and full thickness chondral loss and traumatic bone contusions. He underwent complex knee reconstruction surgery and is currently undergoing rehabilitation in the hospital.

TAWH in blunt trauma occurs due to sudden elevation of intra-abdominal pressure secondary to a large amount of force applied over a small surface area of the abdomen. The tangential forces lead to rupture of abdominal wall muscles and fascia, resulting in subcutaneous herniation of the abdominal viscera, especially bowel loops, through the defect. However, the overlying skin remains intact due to its elasticity.^[1,5] Dennis et al^[6] developed a grading system based on CT imaging to classify TAWH according to the level of injury to abdominal wall. This classification is described in Table 1.

TAWH is more prevalent in younger males, usually less than 50 years of age, as they are more likely to be involved in motor vehicle accidents. The presence of abdominal tenderness, abrasions, ecchymosis or hematoma may be the only clinical findings during examination. Differential diagnosis includes pre-existing hernia, abdominal wall hematoma or tumor. TAWH is rarely isolated and is often accompanied by associated intra-abdominal injuries in 25%-79% of patients.^[4,7] It is common to suffer gastric, intestinal, liver, or splenic injuries as well. Sometimes, injuries to the bowel mesentery may result in bowel ischemia or retroperitoneal hematoma.^[1,2] It is postulated that a high body mass index/obesity and seatbelt-related trauma, as noted in our patient, may also contribute to shearing deceleration forces, thus increasing the incidence of TAWH and associated mesenteric injury.^[8,9]

The diagnosis of TAWH requires a detailed physical examination and a high index of suspicion. The most common clinical feature on examination includes abdominal pain with a tender bulge in the abdominal wall at the site of traumatic hernia. Plain abdominal X-ray examination may show the presence of intestinal loops outside the abdominal cavity. The use of abdominal CT scans in hemodynamically stable patients with blunt trauma has increased, especially in identifying injuries to intra-abdominal organs. CT scans are the imaging modality of choice for the diagnosis of TAWH, as they will provide information regarding the location, size and contents of the hernia as well as the anatomy of the ruptured muscles. TAWH is an important predictor of associated intra-abdominal injuries in patients who suffer from severe trauma, especially radiologically occult mesenteric and serosal/mucosal shearing injuries.^[1,7,8] Occasionally, the hernia can be discovered during a laparotomy performed for other indications, and this then poses a significant challenge to the surgeon who has to decide on the method of reconstruction.

The appropriate timing of surgery for TAWH should be considered on a case-by-case basis, depending on the mechanism and severity of trauma, hemodynamic stability of the patient, the size of the abdominal musculature defect, clinical and radiological findings and other associated injuries.^[10] Trauma protocols for stabilization must be strictly followed in clinically unstable patients. A previous study suggested urgent laparotomy for all patients with TAWH due to the risk of associated bowel or other intra-abdominal organ injuries.^[3] Primary closure in layers of TAWH is usually technically easier than delayed repair. It also reduces the incidence of complications such as strangulation or the need for prosthetic material to close the defect. Early repair with TAWH is safe with a low rate of complications or recurrence.^[3] Patients with small defects may be repaired without prosthetics, but those with large muscular defects or those whose repair has been delayed will require mesh repair. The presence of a hollow viscus injury leading to contamination is usually a contraindication to the use of mesh repair, due to the high risk of infection.^[1] When emergency surgical intervention is not needed, repair of the hernia defect may be delayed. If TAWH is not identified early or in cases of delayed repair, potential complications include intestinal obstruction, strangulation and recurrent abdominal wall herniation. The risk of incarceration and strangulation varies between 10% and 25%.^[7]

TAWH presents a diagnostic challenge in patients presenting with blunt trauma. Due to its rarity, as well as subtle presentation with other distracting injuries, TAWH is often missed. CT scans are the imaging modality of choice to diagnose and classify TAWH and to look for other intra-abdominal injuries. Although not immediately life-threatening, identification of this condition is crucial to guide appropriate surgical management and avoid potential complications.

Funding: This manuscript did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.

Ethical approval: Informed written consent was obtained from the patient.

Conflicts of interest: All authors declare that they have no conflicts of interest.

Contributors: SP conceptualized and drafted the initial version of the manuscript. All authors revised and edited the manuscript. All authors accept the final version of the manuscript.