Pneumoperitoneum due to pneumothorax in blunt thoracoabdominal trauma: A diagnostic challenge

Introduction The presence of pneumoperitoneum after thoracoabdominal trauma is usually caused by perforation of hollow viscus, requiring surgical exploration for sepsis control (1). Rare causes of pneumoperitoneum have been described, as the air can reach the abdominal cavity from different sources through alternative routes (such as diaphragm, genitourinary tract, abdominal wall or retroperitoneum) (2,3). The characteristics of the trauma forces applied and the imaging results can raise suspicion for those alternative causes of pneumoperitoneum (4). We present a case of pneumoperitoneum after traumatic pneumothorax with diaphragmatic laceration.

of free-fluid in the right subphrenic recess and in the computed tomography (CT) scan moderate right-sided pneumothorax (Figure 1), extensive pneumoperitoneum and fat-stratification near the sigmoid colon ( Figure 2). After the pneumothorax was drained, the patient was taken to the operating room for exploratory laparotomy. Intra-operative findings included a diaphragmatic laceration of 5 cm (Figure 3), a non-expansive haematoma of the sigmoid mesocolon and the absence of hollow viscus perforation after thorough abdominal exploration. The diaphragmatic defect was closed with non-absorbable continuous suture reinforced with non-absorbable ePTFE (expanded polytetrafluoroethylene) mesh overlapping the defect. No bowel resection was done after signs of tissue ischemia on the sigmoid colon where excluded. On the third postoperative day, a small amount of right subphrenic fluid and right pleural effusion were identified without signs of infection. No other adverse events or surgical complications were identified and the patient was discharged on the sixth postoperative day.

Discussion
High intensity blunt trauma is associated with a myriad of internal lesions that should be interpreted as a whole clinical picture, alongside with the characteristics of the Case Report Volume 8, Issue 1, 2022, p. 80-82 forces involved. The identification of pneumoperitoneum after a blunt thoracoabdominal trauma is associated with perforation of hollow viscus in the vast majority of cases, however the air may come from different parts of the body following a pressure gradient to the abdominal cavity (1-3).
After blunt thoracic trauma, pneumothorax is a relatively common finding with high intensity forces, generally associated with rib fractures. Usually a positive pressure gradient of 7 to 20 cm of water exists between the peritoneal and pleural spaces but the presence of pneumothorax increases the pleural space pressure. Also, Grosfeld et al found that when a pressure of 60 cmH2O in the pleural space is achieved, subcutaneous emphysema and pneumoperitoneum can occur. The presence of a diaphragmatic laceration enables the flow of air to the peritoneal space in lower pressures, further aiding the association of pneumothorax and pneumoperitoneum (5,6).
Traditionally, the identification of pneumoperitoneum in a trauma patient demands prompt surgical exploration, but several studies have identified a low specificity for hollow viscus perforation in CT scan detected pneumoperitoneum, allowing for a more conservative management of some selected patients, such as a haemodynamically stable patient, with no peritoneal irritation findings and low volume pneumoperitoneum without other abdominal findings suggestive of perforation or additional lesions. The associated presence of clinical signs of peritoneal irritation significantly increases the specificity of CT scan detected pneumoperitoneum for hollow viscus perforation (4,7).
Identification and drainage of a pneumothorax before tracheal intubation is of utmost importance to avoid the development of a tension pneumothorax once positive pressure is created and mechanical ventilation is initiated.
The diagnosis of an unusual origin for the pneumoperitoneum should only be made after thorough exploration of the abdominal cavity and exclusion of more common aetiologies (such as bowel perforation) and other associated gastrointestinal lesions are taken into account.
The reported overall incidence of diaphragmatic hernias after blunt thoraco-abdominal trauma is between 1% and 20% with a great percentage of these unidentified in the inciting episode. Left-sided hernias are more common possibly due to the protective effect of the area covered by the liver on the right side and more fibrous tissue on the  left. Recently, the common use of preoperative CT scans decreased the number of undiagnosed diaphragmatic hernia (DH's). Repair of DH's should be done once the defect is recognized, if possible in the inciting event, avoiding late complications of strangulation. Primary repair is possible if the defect is small and no tension on the repaired tissue is present. In case of a large defect, severe tissue damage or primary repair under tension, mesh repair is recommended to reduce recurrence, but no consensus on mesh type is found in the literature. In cases of contaminated field, such as concomitant bowel perforation, use of biological mesh is an option to reduce infection rate (8).
In the case described, the presence of pneumothorax, several rib fractures and subcutaneous emphysema could raise the suspicion for an alternative origin for intra-peritoneal free air. But peritoneal irritation signs were present and CT scan showed alterations of the mesosigmoid, consequently, urgent surgical exploration was performed. The diaphragmatic defect was corrected with mesh placement due to concern on tissue tension after simple closure.

Conclusion
Pneumoperitoneum after blunt abdominal or thoracoabdominal trauma is not always due to hollow viscus perforation and other sources of free intraperitoneal air should be considered, particularly in high intensity settings.
Careful selection of patients to undergo conservative management can be useful to avoid the high morbidity and mortality of an urgent surgical exploration. However, the presence of peritoneal irritation signs, haemodynamic instability or suspected multiple injuries warrants surgical exploration either by a laparoscopic or an open approach. Thoracic drainage is mandatory in every case of pneumothorax before starting invasive ventilation to avoid creating a tension pneumothorax.
Authors' contributions RMM, CFB and CV: Surgical Team, Scientific review AL: Scientific review. All authors made substantial contribution to the conception and design of the work and to the drafting and revision of the article content. The final version submitted as the approval of all authors which are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Ethical issues
Informed consent statement was obtained from the patient for the publication of this report.