Ilya Sabsovich, MD
Surgical and Trauma Intensive Care Unit
Elmhurst Hospital Center
Elmhurst, NY
Department of Surgery
Mount Sinai School of Medicine
New York, NY

Ravi Desai, MD
The Mount Sinai Hospital
Department of Surgery
Mount Sinai School of Medicine
New York, NY

Rafael Alba, MD
International Physician
Universidad Iberoamericana School of Medicine
Santo Domingo, Dominican Republic

Jose Yunen, MD
Director
Cardiothoracic Intensive Care Unit
Infectious Diseases and Critical Care Medicine
Montefiore Medical Center
Albert Einstein College of Medicine
Bronx, NY

David Sammett, MD
Surgical and Trauma Intensive Care Unit
Elmhurst Hospital Center
Elmhurst, NY

ABSTRACT

Introduction: Pneumoperitoneum (PP) secondary to blunt abdominal trauma is rarely observed in adults whose viscus has not ruptured. The condition is encountered even less frequently in blunt thoracic trauma patients, who are more likely to present with pneumothoraces, pneumomediastinum, or pneumopericardium.

Results and discussion: Because of the increased use of computed tomography and its high sensitivity, PP often may be an incidental finding in blunt trauma patients. The authors report one such case in a patient who was thrown off his motorcycle when it collided with a motor vehicle. The patient had PP although his viscus did not rupture. The authors provide a comprehensive discussion on the etiology of PP and provide insights on how it may occur in the absence of a ruptured viscus.

Conclusion: Complications from missed intra-abdominal injuries can be disastrous; thus, once PP is identified, exploratory laparotomy is almost always warranted. If a patient’s PP is thought to originate from a benign cause and conservative management is elected, the patient’s vital signs must be monitored closely and serial examinations of the abdomen must be undertaken along with frequent laboratory evaluations.

Pneumoperitoneum (PP) is a striking radiological finding that is almost always indicative of severe intraabdominal disease. It is generally accompanied by prominent clinical symptoms and physical findings consistent with peritonitis, and the need for immediate surgical intervention is apparent. Ninety percent of PP cases result secondary to a perforated viscus and demonstrate intraperitoneal free air on radiography.¹ The remaining 10% of cases are attributable to a variety of nonpathologic causes that result in free subdiaphragmatic air but may not require surgical intervention. Such cases have been referred to as "idiopathic" or "spontaneous" PP.¹ The origin of air in these cases generally can be attributed to air leakage from pneumatosis cystoides intestinalis,² a small perforated duodenal ulcer,^1,3 a minute leak from a colonic diverticulum,⁴ insufflation of air through the female genital tract,^5,6 chronic obstructive pulmonary disease,^7,8 cardiopulmonary resuscitation,⁹ or mechanical ventilation.^8,10,11

Another type of idiopathic PP, which is far rarer, is associated with pneumothorax secondary to trauma.^8,11-15 In these cases, thoracic air is introduced through a rupture of the lungs and dissects retroperitoneally or leaks directly through defects in the diaphragm.¹⁶ The diagnosis of PP in this group of patients does not invariably mean gastrointestinal perforation and, therefore, does not always require operation. Conservative management with prudent judgment and meticulous observation may avoid unnecessary surgery in these patients.

CASE REPORT

A 24-year-old man was riding a motorcycle when he collided with a sports utility vehicle and sustained major injuries. While being transported to the hospital by emergency medical services, he developed significant respiratory distress. A needle thoracocentesis was performed on the right side for tension pneumothorax, which promptly improved his symptoms. On arrival to the emergency department, he underwent placement of a chest tube on the same side as the needle decompression.

Figure 1—CT scan of the chest showing pneumothorax, pneumomediastinum, pneumopericardium, and subcutaneous emphysema.

The patient was initially hypotensive, with a blood pressure of 88/55 mm Hg (normal, 100-to-119/60-to-79 mm Hg). After resuscitation with crystalloids, his systolic blood pressure improved to 120 to 130 mm Hg, but he remained tachycardic. There were no lateralizing neurologic signs, and he scored a 15 on the Glasgow coma scale (a score of 13 to 15 indicates mild head trauma, whereas a score of 3 to 8 indicates coma). An admission hemogram, urinalysis, and blood chemistries were within normal limits. A bedside transthoracic echocardiogram showed normal systolic function without wall-motion abnormalities.

A computed tomography (CT) scan of the patient's chest showed multiple rib fractures bilaterally, bilateral pulmonary contusions, bilateral pneumothoraces, extensive right chest wall subcutaneous emphysema, and a sternal fracture (Figure 1). Pneumomediastinum and pneumopericardium were observed. The great vessels and the tracheobronchial tree were intact. There was no evidence of hemothorax. A CT scan of the abdomen and pelvis showed a splenic laceration and PP without any other intraabdominal or intrapelvic injuries (Figure 2). The decision was made to perform an urgent exploratory laparotomy to rule out injury to a hollow viscus.

A left-sided chest tube was placed, and the patient was brought to the operating room, where he was intubated and ventilated. Intraoperatively, the patient was found to have a large abdominal wall injury in the right upper quadrant just below the diaphragm, with an adjacent nonexpanding retroperitoneal hematoma and a small mesenteric hematoma. The splenic hilum was disrupted and actively bleeding, necessitating a splenectomy. Careful inspection of the viscera did not reveal any evidence of bowel perforation and the diaphragm was found to be intact. The extrahepatic biliary tract was uninjured.

The patient's postoperative recovery was complicated by acute respiratory distress syndrome and persistant pneumothorax on the right side. He was discharged from the hospital in good condition on postoperative day 14.

DISCUSSION

PP is an alarming radiographic finding that is almost always pathognomonic of a ruptured viscus and usually requires immediate exploratory laparotomy. In cases of blunt chest or abdominal trauma, CT scanning is a mandatory part of the evaluation; however, it is not known whether finding free intraperitoneal air on the CT scans of a trauma patient reliably indicates gastrointestinal perforation. In a series by Kane and colleagues, CT scanning was done routinely in evaluating blunt abdominal trauma patients, and free air was associated with a ruptured viscus only 22% of the time.¹⁷ The clinical significance and outcomes of CT-detected PP in blunt trauma patients raises two questions: What is the pathophysiology of CT-detected PP in the setting of blunt chest or abdominal trauma with no evidence of bowel perforation? And, what management protocol should be followed for blunt trauma patients after PP is detected with CT scanning?

The association between pneumothorax and idiopathic PP has been reported in several case studies of patients who have sustained blunt trauma.^8,11-15 In the study by Kane and colleagues, pneumothorax was found in 50% of blunt trauma patients with CT-detected PP.¹⁷ None of these patients had bowel perforation. Because intraabdominal pressure exceeds intrathoracic pressure by an average of approximately 20 to 30 cm H₂O during both inspiration and expiration, 18 simple pneumothorax should not lead to PP. Even patients with tension pneumothorax develop this complication infrequently due to the rapidity of treatment or inadequate buildup of intrathoracic pressure.⁸ These findings suggest that very high intrathoracic pressure is required to cause dissection of air through the retroperitoneal space.

Speculation on the etiology of PP without pneumothorax

Figure 2—CT scan of the abdomen and pelvis showing pneumoperitoneum.

No definitive explanation exists for the presence of PP in blunt trauma patients without concomitant pneumothorax. The speculation is that the free intraabdominal air in these patients may have resulted from intestinal microperforations, which rapidly seal and leave behind no obvious clinical sequelae. This is akin to the well-described clinical entity of pneumatosis cystoides intestinalis, which is a rare cause of PP after blunt abdominal trauma.⁷ In this syndrome, airfilled sacs develop in the bowel wall as a result of mucosal microperforations through which air transects into the intestinal serosa.⁷ Intraperitoneal free air results when these sacs rupture.

The association of mechanical ventilation with pneumothorax increases the risk of air dissection into the peritoneal cavity. Laboratory experiments by Grosfeld and associates in the early 1970s show that interstitial emphysema develops when intratracheal pressures exceed 40 cm H₂O.¹⁹ Pneumomediastinum develops at pressures of 50 cm H₂O, and subcutaneous emphysema accompanied by PP can appear at pressures of 60 cm H₂O and greater. It is thought that air leaking from ruptured alveoli collects in the interstitial space. As intrathoracic pressure increases, the air dissects along the sheath of adjacent vessels into the mediastinum. The air can then dissect into various spaces, including the pleural space and along the thoracic great vessels and esophagus into the retroperitoneum, where it may rupture into the peritoneal cavity and cause PP.¹⁹

Ventilatory pressures and PP

Other literature shows that overinflation of the lungs with high ventilatory pressures can cause air to dissect along the esophagus and aorta, resulting in pneumoretroperitoneum.²⁰ After conducting seminal experiments in 1937, Macklin concluded that air leaking from ruptured alveoli travels along the perivascular sheaths of the mediastinum and retroperitoneum, ultimately reaching the peritoneal cavity and causing PP.²⁰ Alveoli rupture most commonly occurs around the kidneys.²⁰ Operation is not deemed necessary in these cases.

Some posttraumatic patients with pneumothorax developed PP following mechanical ventilation.^11,13,15 This likely resulted when air dissected into the peritoneum. The studies by Macklin and later by Grosfeld and associates demonstrate how high intratracheal pressure and overinflation of the lungs can cause pneumoretroperitoneum and subsequent PP.^19,20 It seems that in patients on mechanical ventilation, especially those with pneumothorax and subcutaneous emphysema, the appearance of free intraperitoneal gas does not necessarily indicate a surgical emergency.¹⁰

An unusual presentation

The blunt trauma patient described in our case report developed bilateral pneumothoraces, pneumomediastinum, and PP. There was no clinical evidence of a perforated viscus, and he was not being mechanically ventilated. The patient's pneumothoraces were thought to be due to his fractured ribs. High intrathoracic pressures forced air into the abdomen either directly across a defect in the diaphragm or indirectly through the mediastinum retroperitoneally. Rupture of the diaphragm, which is an unusual injury following blunt abdominal trauma, must be suspected in all patients with massive trauma.¹⁶ Our patient's clinical picture and imaging studies, along with a careful examination of his diaphragm during exploratory laparotomy, did not show diaphragmatic rupture. One plausible explanation of his PP is that very high intrathoracic pressure following the initial impact caused bilateral pneumothoraces and pneumomediastinum, leading to dissection of air through the mediastinum into the retroperitoneum and, finally, to the peritoneal cavity. The high pressure of the tension pneumothorax was treated by emergency medical services and again in the emergency department; thus, our patient's PP most likely occurred on impact or immediately thereafter.

CONCLUSION

The dilemma for surgeons is deciding whether CT-detected PP in posttraumatic patients with concurrent pneumothorax is attributable to a benign abnormality or whether it indicates a potential surgical emergency. In the study by Kane and colleagues, approximately 80% of blunt trauma patients with CT-detected PP did not have an abdominal injury requiring surgery; however, the series in this study was too small to make a legitimate statistical analysis.¹⁷

When there is a question as to whether an operation is warranted in a trauma patient with pneumothorax, pneumomediastinum, and CT-detected PP, the CT findings need to be assessed very carefully. CT findings that mandate a trip to the operating room include free peritoneal fluid and mesenteric or bowel wall thickening. If CT findings are questionable and conservative treatment is elected, then serial examinations of the abdomen (preferably by the same clinician), frequent laboratory examinations, and constant monitoring of vital signs must be undertaken.

REFERENCES

1. McGlone FB, Vivion CG Jr. Spontaneous pneumoperitoneum. Gastroenterology. 1966;51:393-398.
2. Sweriduk ST, Deluca SA. Pneumatosis cystoides intestinalis. Am Fam Physician. 1985;32:113-114.
3. Britt CI, Christoforidis AJ, Andrews NC. Asymptomatic spontaneous pneumoperitoneum. Am J Surg. 1961;101:232-235.
4. Besic N, Zgajnar J, Kocijancic I. Pneumomediastinum, pneumopericardium, and pneumoperitoneum caused by peridiverticulitis of the colon: report of a case. Dis Colon Rectum. 2004;47:766-768.
5. Dodek SM, Friedman JM. Spontaneous pneumoperitoneum. Obstet Gynecol. 1953;1:689-698.
6. Wright AR. Spontaneous pneumoperitoneum. Arch Surg. 1959;78: 500-502.
7. Gantt CB Jr, Daniel WW, Hallenbeck GA. Nonsurgical pneumoperitoneum. Am J Surg. 1977;134:411-414.
8. Glauser FL, Bartlett RH. Pneumoperitoneum in association with pneumothorax. Chest. 1974;66:536-540.
9. Clinch SL, Thompson JS, Edney JA. Pneumoperitoneum after cardiopulmonary resuscitation: a therapeutic dilemma. J Trauma. 1983;23:428-430.
10. Altman AR, Johnson TH. Pneumoperitoneum and pneumoretroperitoneum. Consequences of positive end-expiratory pressure therapy. Arch Surg. 1979;114:208-211.
11. Andrew TA, Milne DD. Pneumoperitoneum associated with pneumothorax or pneumopericardium: a surgical dilemma in the injured patient. Injury. 1979;11:65-70.
12. Hashmi S, Rogers SO. Tension pneumothorax with pneumopericardium. J Trauma. 2003;54:1254.
13. Gardner-Thorpe D, Maddox PR. Idiopathic pneumoperitoneum following blunt chest trauma: a case report. Injury. 1999;30:511-513.
14. Hamilton P, Rizoli S, McLellan B, et al. Significance of intraabdominal extraluminal air detected by CT scan in blunt abdominal trauma. J Trauma. 1995;39:331-333.
15. Krausz M, Manny J. Pneumoperitoneum associated with pneumothorax: a surgical dilemma in the posttraumatic patient. J Trauma. 1977;17:238-240.
16. Ferrera PC, Chan L. Tension pneumoperitoneum caused by blunt trauma. Am J Emerg Med. 1999;17:351-353.
17. Kane NM, Francis IR, Burney RE, et al. Traumatic pneumoperitoneum. Implications of computed tomography diagnosis. Invest Radiol. 1991;26:574-578.
18. Rushmer RF. The nature of intraperitoneal and intrarectal pressure. Am J Physiol. 1946;147:242-249.
19. Grosfeld JL, Boger D, Clatworthy HW Jr. Hemodynamic and manometric observations in experimental air-block syndrome. J Pediatr Surg. 1971;6:339-344.
20. Macklin D. Pneumothorax with massive collapse from experimental local overinflation of the lung substances. Can Med Assoc J. 1937;36:414-420.

1. Pneumoperitoneum (PP) is a radiological finding that almost always indicates
   1. Idiopathic intraabdominal pathology
   2. Air leakage from pneumatosis cystoides intestinalis
   3. Pneumothorax secondary to trauma
   4. A ruptured viscus
       
2. Following negative plain films, which imaging modality could be used to reliably diagnose pneumoperitoneum?
   1. Magnetic resonance imaging with gadolinium
   2. Computed tomography (CT) scanning without intravenous or oral contrast
   3. Complete abdominal ultrasonography
   4. White blood cell scan
       
3. Which CT findings warrant operating on a trauma patient who has been found to have pneumothorax, pneumomediastinum, and PP?
   1. Free intraperitoneal fluid
   2. Mesenteric wall thickening
   3. Bowel wall thickening
   4. All of the above
       
4. A middle-aged man is admitted to the intensive care unit with respiratory failure complicating pneumonia secondary to Legionella infection. Mechanical ventilation with positive endexpiratory pressure is initiated. Radiographs of the chest reveal pneumomediastinum and PP, but there is no evidence of air in the pleural cavity. An abdominal examination reveals no abnormalities. What is the next step?
   1. Exploratory laparotomy
   2. Chest tube placement
   3. Observation
   4. Administration of antibiotics

Read the Answers

Answers

1. d—In 90% of cases, PP indicates a ruptured viscus and requires immediate surgical intervention. The other 10% of cases can be considered idiopathic or spontaneous and result from causes that may not warrant an operation. In rare cases, PP may result from pneumothorax secondary to trauma.
2. b—Although air or gas in the peritoneal cavity can be seen on radiography, small amounts of gas may be missed. CT scanning can reveal small amounts of gas and is considered the gold-standard in assessing PP. According to animal studies, CT scanning can depict as little as 5 cc of free air in the peritoneum.* In cases of perforation, inflammatory fluid collections may be observed within the peritoneum. This fluid is readily detected on CT scanning and the cause of the perforation sometimes can be diagnosed. The most commonly observed perforation is a ruptured abdominal viscus secondary to a perforated peptic ulcer, but any part of the bowel may perforate from a benign ulcer, tumor, or trauma. A much rarer form of idiopathic PP is trauma-induced pneumothorax.
   *Khan AN. Pneumperitoneum. Available at: www.emedicine.com/Radio/topic562.htm. Accessed March 28, 2008.
3. d—When there is a question of whether an operation is warranted in a trauma patient with pneumothorax, pneumomediastinum, and CT-detected PP, the CT findings need to be assessed carefully. Findings that mandate a trip to the operating room include free peritoneal fluid and mesenteric or bowel wall thickening.
4. c—PP in the setting of mechanical ventilation, without evidence of visceral perforation, usually can be managed conservatively. Investigators have shown that overinflation of the lungs with high ventilatory pressures can cause air to dissect along the esophagus and aorta and cause pneumoretroperitoneum. The theory is that air leaking from ruptured alveoli travels along the perivascular sheaths of the mediastinum and retroperitoneum, ultimately penetrating the peritoneal cavity and causing PP. The most common site of peritoneal rupture is around the kidneys. In most cases, PP resulting from mechanical ventilation can be managed conservatively with meticulous observation.