Traumatic abdominal wall hernia
Synonyms and keywords: TAWH

# Overview
Traumatic Abdominal Wall Hernia (TAWH) represents an infrequent form of hernia and constitutes 1% of hernia cases.

# Historical Perspective
The first case was reported by Selby in 1906.

# Epidemiology and Demographics
There have been 100 cases reported worldwide. The frequency of cases has increased in the last two decades.

# Classification
Traumatic abdominal wall hernia is generally classified into three types 
- A small abdominal wall defect caused by low-energy trauma with small instruments (e.g. bicycle handlebar)
- A larger abdominal wall defect caused by high-energy transfer such as motor vehicle accident or a fall from a height
- Iintra-abdominal herniation of bowel with deceleration injures (rare)

# Pathophysiology
TAWH is defined as herniation of viscera occurring after a force is applied to the abdomen in a patient without preexisting abdominal hernia, resulting in disruption of muscles and fascia while maintaining skin continuity.  The mechanism of TAWH is thought to be caused by shear stress associated with acute elevation of intra-abdominal pressure.  The shear stress is transferred to the peritoneum, fascia and muscle fibers which is then followed by tissue rupture.  These injuries are mostly located below the umbilicus due to weaker musculature in that region since the rectus sheath is present only above the arcuate line.  The hernia may occur at a site fremote from the initial site of trauma. When traumatic insult to the abdominal wall is mainly due to shearing stresses or tensile forces, intra-abdominal injuries are extremely uncommon.

# Diagnosis
The criteria for diagnosing TAWH were suggested by McWhorten in 1939, and they are:
- Immediate occurrence following blunt trauma
- Severe pain at the site of the injury
- Patient presents within the first 24 hours
- No previous hernia.
Later, these criteria were modified to include:
- Intact Skin over the hernia and
- No evidence of hernial sac during surgery

## Symptoms
The majority of these patients present immediately following the trauma, and 26% present later.

## Physical Examination
The classical signs of hernia (i.e., cough impulse and reducibility) are present in only 50% of patients, thus it can be confused with a hematoma. An interesting feature recorded in such a situation is the tendency of such hernias to increase in size over a short period of time. Bowel sounds can occasionally be heard over such a swelling.

## Imaging
Ultrasound of the abdominal wall is still widely used because of its availability and relatively low cost. For the first evaluation in the emergency room, ultrasound is easily accessible and can be helpful in establishing the primary diagnoses. However, the sensitivity and specificity of the CT scan is much higher and also enables better imaging of the abdominal wall and the intra-abdominal organs which is of interest in the abdominal trauma patient. At present, CT scan is the standard for diagnosing of any form of abdominal wall hernia since the relationship between the different muscle layers and surrounding structure is better visualized.

# Treatment
Surgical intervention remains the mainstay of management in these patients, although conservative management has been reported in the literature. There is controversy as to whether to operate immediately or later.  The majority of surgeons prefer to operate immediately, and some after a period of conservative management.  The timing of surgery depends on the following considerations:
- Surgeon preference
- The timing of presentation
- Comorbidities and fitness for surgery
- The presence of complications
- The hemodynamic status and severity of associated injuries
Complications that should be avoided with surgery include incarceration and strangulation of the bowels.
Despite the trend to use the laparoscopic approach in treatment of incisional hernias, it infrequently practiced in cases of TAWH. Open surgery was selected in most of the reported cases in the literature. Debates exist on whether to use a midline incision or an incision over the hernia. In the majority, midline incision was chosen in acute cases, to rule out associated intra-abdominal injury which occurs in about 30 % to 44% of patients in high energy trauma. While in low energy induced TAWH, local exploration through an incision over the hernia is preferred.
The main goal of surgery is reconstruct the disruption of the abdominal wall, which can be achieved either by primary closure or by applying a mesh. It depends on the size and site of hernia, associated intra-abdominal injury and timing of intervention. In TAWH induced by low energy, a primary repair, by approximation of the defect using non-absorbable sutures, was the first choice, because in these cases the soft tissue damage and defect size is minimal. On the other hand, in high energy TAWH, the defect size is usually larger and tissue loss is greater, which cant be repaired primarily. So mesh is preferred, with additional benefit by decreasing the recurrence rate. But not to forget the increased risk of infections in these circumstances.