Blunt abdominal injury causes high morbidity and mortality and accounted for 79% of trauma death. [1] Of all the injuries, hollow viscous injury is more frequent in the presence of an associated severe solid organ injury, particularly to the pancreas. Therefore, expedient diagnosis and treatment of intra-abdominal injuries are essential to avoid preventable disability and death. One of the common signs of hollow viscous injury is the presence of air under the diaphragm. Refinement in diagnostic capabilities have allowed a more selective application of laparatomy to the trauma patients at risk for abdominal injury and has reduced the number of non-therapeutic laparatomy without increasing morbidity and mortality from abdominal trauma.

Indications for exploratory laparatomy for blunt abdominal trauma can be undertaken on the basis of physical examination findings alone or on the basis of results of further diagnostic tests. Clinical findings include obvious peritoneal signs and hypotension with a distended abdomen. [2] Diagnostic tests available to assist the physician in the emergency department include supine abdominal X-ray, erect chest X-ray, abdominal ultrasonography, computed tomography (CT) scan of the abdomen and laparoscopic examination.

We describe a case of suspected perforated viscus with positive findings on abdominal radiograph and CT of abdomen (pneumoperitoneum) but negative explorative laparatomy. In these cases, careful observation and monitoring may avoid unnecessary surgery and related complications. The purpose of this case report is to highlight the advantages and disadvantage of various investigations used to detect the intraabdominal injury.

A 19-year-old male motorcyclist alleged a collision with a cow. The cow died instantly and his bike was badly damaged. He was brought by the passerby to the nearest hospital (Hospital Kuala Terengganu is about 160 km distant from Hospital Universiti Sains Malaysia (HUSM)). He had sustained severe head injury with GCS of 8/15. He was intubated, ventilated and immediately referred to neurosurgical department of HUSM for urgent CT brain and possibility of surgical intervention.

Initial primary survey (upon arrival to the Emergency Department (ED) of HUSM) revealed he was hypoxic, with diminished breath sounds and hyper resonance over the right lung. His blood pressure, pulse rate and pulse oximetry were 165/114 mmHg, 130 beats/min and 83% respectively. A diagnosis of right pneumothorax was made and needle thoracostomy procedure was commenced immediately. Subsequently, oxygen saturation improved (96%) and chest tube was inserted. Supine chest radiograph after the procedure revealed pneumothorax of left lung (figure 1). Then another chest tube was inserted on the left side.

Further primary survey assessment revealed that the right pupil was dilated. CT brain was ordered immediately. Secondary survey revealed rhinorrhea, subcutaneous emphysema over the neck extended to upper abdomen and right 4th and 5th metacarpal fracture. Abdomen examination was normal. Focus Abdominal Sonography in Trauma (FAST) was unable to visualize free fluid or solid organ injury. CT brain revealed a large extradural hemorrhage at the right temporal region. It measures 4.8 cm (CC) x 3 cm (AP) x 2 cm (width). There was also an extradural hemorrhage at the right parietal region. It measures 2.3 cm (width) x 7.6 cm (AP) x 7.5 cm (CC). It caused compression of the ipsilateral lateral ventricle and a subfalcine herniation. On bone window, there was a comminuted depressed right parietal bone fracture. Air pocket was noted in the left temporal region, right orbit and between muscle planes of neck and prevertebral area. CT scan of thorax revealed pneumomediastinum with bilateral basal lung contusion and pneumothorax. Contrast enhanced CT (CECT) scan of the abdomen demonstrated pneumoperitoneum and pneumoretroperitoneum. There was absence of peritoneal free fluid and solid organ injury (figure 2 A, B).

Neurosurgical team commenced emergency right temperoparietal craniotomy and evacuation of extradural hemorrhage. Later, the surgical team performed exploratory laparotomy. Intra-operative findings of laparatomy included presence of multiple retroperitoneal bubbles surrounding the splenic flexure, no solid organ injury seen and no alimentary tract perforation. Both surgeries went successfully. Postoperative period was uneventful. On day-21, post-trauma, he was discharged home.

The goal of the initial evaluation of blunt abdominal trauma is to expeditiously identify patients who require laparatomy and prompt repair of the intra-abdominal injuries. Unfortunately, victims involved in high velocity accidents are difficult to assess, especially those associated with closed head trauma, under influence of alcohol or drugs and poly trauma. Therefore, diagnostic modalities beyond physical examination are required to identify the injury promptly.

Pneumoperitoneum may occur as a result of perforated viscus secondary to pathologic process of the alimentary system or as a result of trauma. Air under the diaphragm is a radiological finding viewed from a chest radiograph that suggests intraperitoneal gas. Other features of intraperitoneal gases can be detected via plain supine abdominal radiograph. The features include Rigler's sign ("double wall sign"), football sign or falciform ligament sign (Silver's sign).

Our patient underwent emergency laparatomy based on the evidence of significant high impact injury, air under diaphragm on supine chest radiograph and evidence of pneumoperitoneum from a report of CECT of the abdomen. Abdominal CT is more sensitive and superior to upright chest radiograph in demonstrating free intraperitoneal air. However, pneumoperitoneum finding on abdominal CT is not pathognomonic of bowel perforation. [3] The detection of pneumoperitoneum has obvious significant surgical implications.

Plain supine chest radiograph for this patient was utilized to assess the lung fields and to reveal a ruptured hemi-diaphragm or pneumoperitoneum if present. Approximately one half of patients with pneumoperitoneum have gas in the right upper quadrant on plain radiograph. [4] Unfortunately, the available evidence suggests that an erect posteroanterior chest radiograph is not sufficiently sensitive to rule out pneumoperitoneum. The sensitivity of penumoperitoneum detection might be improved by performing either an erect lateral chest radiograph or computed tomography. [5]

Unfortunately, in emergency setting when the patients are critically ill, the chest radiograph is almost always done in supine position instead of standard erect position. Some of them require intubation and ventilation prior to the chest radiograph and later they may suffer from pneumothorax. Air under diaphragm on supine chest radiograph may mislead in making the wrong diagnosis. Obviously, when the chest X-ray is taken in the upright position, gas being lighter rises up and settles under the diaphragm and is seen in the X-ray as a radiolucent (dark) area. In contrary, if the patient is supine when the X-ray is taken, the gas will settle at the region of the umbilicus and hence such a film is not useful in diagnosing hollow viscous perforation.

In this case, it is important to emphasize the various causes of air under diaphragm seen in the chest radiograph since the patient had normal and soft abdomen on palpation and was hemodynamically stable. Pneumoperitoneum resulting from a perforated hollow viscus in 90% of the cases causes peritonitis and requires immediate surgical intervention. [10] Free intraperitoneal air is not necessarily caused by alimentary tract perforation. [11] Other clinical conditions that may mimic pneumoperitoneum include Chilaiditi syndrome, basal lung bulla, undulating diaphragm, subphrenic abscess due to gas forming organisms, pyonephrosis due to gas forming organisms, subphrenic fat and pneumoretroperitoneum. [5]

Radiological finding of air under diaphragm in a patient with pneumothorax or ventilated patient with absence of peritonism needs to be interpreted cautiously. Pneumoretroperitoneum can mimic pneumoperitoneum in chest radiograph. CT abdomen may eliminate this problem. It is vital to establish the diagnosis of perforated bowel. If the diagnosis of perforated hollow viscus can be eliminated with considerable certainty, then conservative management with careful observation and monitoring may avoid unnecessary surgery. Unfortunately in our case, even the CT abdomen demonstrated pneumoperitoneum.

Pneumoperitoneum is an expected finding in patients on positive end-expiratory pressure therapy. Anterior mediastinal air can enter the peritoneal cavity, particularly in patients with a history of median sternotomy. [6] Radiological finding of air under the diaphragm can be observed in about 10% of patients with pneumomediastinum, pneumothorax and in patient on mechanical ventilation. [7] Pneumoretroperitoneum can occur in the presence of pneumomediastinum secondary to barotrauma from mechanical ventilation. [8] It is thought to arise from alveolar rupture into the bronchoalveolar sheath with dissection through the pulmonary interstitium toward and into mediastinum and then further dissection can occur into the neck superiorly and into the retroperitoneum inferiorly. Frequently dissection occurs with a subsequent pneumothorax. [9] Air can also leak from the alveolus to the mediastinum via pores of Kohn. [10] There is a tissue plane that extends anteriorly from the mediastinum to the retroperitoneal space through the sternocostal attachment of the diaphragm. This anterior pathway of infradiaphragmatic extension of air can be erroneously diagnosed as intraperitoneal air, which may lead to unnecessary exploratory laparotomys. The mediastinum also communicates directly with the retroperitoneum by way of the periaortic and perioesophageal fascial planes. [11] In this patient tracking from a pneumomediastinum is the most likely cause of pneumoperitoneum.

In such a complicated presentation of traumatic patient, a diagnostic peritoneal lavage (DPL) will be beneficial [12] for those patients who are suspected to have hollow visceral injury based on physical examination and/or CT findings, those who may have suffered abdominal trauma, those with multiple injuries, those with disturbance of consciousness due to head injury, or those under sedation for respiratory support. DPL using Otomo's criteria and the cell count ratio is highly predictive of the presence of blunt hollow visceral injury. [13] To avoid similar problem in the future, we suggest diagnostic peritoneal lavage (DPL) after CT abdomen for identifying blunt hollow visceral injury. The combined application of the two criteria improves the accuracy of diagnosing blunt hollow visceral injury, thereby enabling surgeons to avoid unnecessary celiotomies.

In conclusion, this case provides additional evidence that the presence of pneumoperitoneum on chest radiograph and CT abdomen are just plain radiological findings. It does not always indicate pneumoperitoneum secondary to perforations of the alimentary tract. Appropriate diagnosis avoids invasive procedure.

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