Introduction
The presence of gas under the diaphragm, also known as pneumoperitoneum, is a critical finding in medical imaging, most notably on erect chest or abdominal radiographs. While often indicative of a serious underlying condition requiring prompt surgical intervention, the most common culprit being hollow viscus perforation, a significant minority of cases, approximately 10%, arise from less frequent and often more challenging to diagnose etiologies. These rarer causes span both abdominal and extra-abdominal origins, including intra-abdominal infections caused by gas-forming organisms. This article delves into the differential diagnosis of air under the diaphragm, presenting a unique case of pancreatic abscess manifesting as pneumoperitoneum and emphasizing the importance of considering atypical presentations in clinical practice. Understanding the diverse range of conditions that can lead to air under the diaphragm is crucial for accurate diagnosis and timely management, particularly in cases where the presentation deviates from the typical scenario of a perforated viscus.
Case Presentation: Atypical Pneumoperitoneum from Pancreatic Abscess
We present the case of a 51-year-old male patient with a history of poorly controlled diabetes mellitus, who presented to the emergency department with a recurrent episode of severe abdominal pain and distention. He described the pain as worsening over three days, accompanied by mild abdominal distention and fever onset within the last 24 hours. Notably, he denied any back pain radiation. Three weeks prior, he experienced a similar episode of moderate abdominal pain in the periumbilical region, diagnosed as subacute intestinal obstruction based on abdominal X-ray findings of multiple air-fluid levels, which was managed conservatively. Serum amylase and lipase levels were reportedly normal during that initial episode.
Upon examination, the patient appeared distressed and febrile, with vital signs revealing tachycardia (130 beats per minute), hypotension (100/70 mm Hg), and tachypnea (24 breaths per minute). His abdomen was mildly distended and soft on palpation, with tenderness localized to the lower abdomen. Bowel sounds were absent. Rectal examination was unremarkable. Initial investigations revealed: Hemoglobin 11gm/dl; total white cell count 5500/cc; neutrophils 54%; lymphocytes 40%. Liver function tests were within normal limits.
An erect abdominal X-ray was immediately performed, revealing a significant gas shadow under the right dome of the diaphragm (Fig. 1). To rapidly confirm and further assess the pneumoperitoneum, a bedside abdominal ultrasound was conducted, which demonstrated gross pneumoperitoneum, obscuring visualization of upper abdominal viscera. Minimal ascites and bowel/mesenteric wall thickening were also noted. Based on these findings, a provisional diagnosis of intestinal perforation was made, and the patient was prepared for emergency laparotomy. While a CT scan of the abdomen would have been ideal for detailed evaluation, it was deferred due to financial constraints and the urgent clinical situation.
During emergency laparotomy, the surgical team discovered thick purulent fluid emanating from the inferior leaf of the transverse mesocolon, to the left of the duodenojejunal flexure. Remarkably, no hollow viscus perforation was identified (Fig. 2). Further exploration revealed an inflammatory mass within the lesser sac, originating from the body and tail of the pancreas, actively discharging yellow pus. A diagnosis of ruptured pancreatic abscess was established. The abscess was meticulously debrided, and drainage was established using two suction drains positioned supero-inferiorly. Postoperatively, continuous irrigation and drainage were performed via these drains using copious amounts of normal saline. The patient’s postoperative course was uneventful. Pus culture yielded Klebsiella species, sensitive to aminoglycosides. Histopathological examination of tissue samples confirmed necrotic pancreatic tissue.
Fig. 1.
Fig. 2.
Differential Diagnosis of Air Under Diaphragm
When encountering air under the diaphragm on imaging, particularly in an erect chest or abdominal X-ray, a comprehensive differential diagnosis is essential. While hollow viscus perforation constitutes the vast majority (approximately 90%) of cases, it is crucial to consider the remaining 10% which encompass a diverse range of less common etiologies. These can be broadly categorized as:
Common Causes (Primarily Hollow Viscus Perforation)
- Peptic Ulcer Perforation: Gastric or duodenal ulcers eroding through the bowel wall are the most frequent cause.
- Appendicitis with Perforation: Ruptured appendix leading to generalized peritonitis and pneumoperitoneum.
- Diverticulitis with Perforation: Perforation of colonic diverticula, especially in the sigmoid colon.
- Traumatic Bowel Perforation: Penetrating or blunt abdominal trauma causing bowel injury.
- Iatrogenic Perforation: Complications from procedures like endoscopy or colonoscopy.
Less Common and Atypical Causes
It is within this category that the importance of a broad differential diagnosis for air under the diaphragm truly emerges. These less common causes, while individually rare, collectively represent a significant clinical challenge:
- Post-Laparotomy Status: Residual air following abdominal surgery, typically resolves within a few days but can persist longer in some cases. Clinical context is paramount.
- Ruptured Liver Abscess: Infection within the liver can rarely rupture into the peritoneal cavity, introducing air and infectious material.
- Retroperitoneal Air: Air tracking from the retroperitoneum, possibly from retroperitoneal infections or instrumentation, can mimic pneumoperitoneum.
- Biliary-Enteric Fistula: Abnormal communication between the biliary system and the intestine can allow air to enter the peritoneum.
- Gallstone Ileus: A large gallstone obstructing the small bowel can, in rare instances, lead to perforation proximal to the obstruction or gas formation due to bacterial overgrowth.
- Incompetent Sphincter of Oddi: Rarely, dysfunction of the Sphincter of Oddi can allow reflux of air into the biliary tree and potentially into the peritoneum.
- Focal Biliary Lipomatosis: A very rare condition, not typically associated with pneumoperitoneum but listed in some broader differentials. Its relevance is questionable in the context of air under the diaphragm.
- Post Scuba Diving (Barotrauma): Alveolar rupture due to pressure changes during diving can result in pneumomediastinum and, rarely, pneumoperitoneum.
- Post Adeno-tonsillectomy: Extremely rare, potentially due to air tracking along tissue planes, more likely to cause pneumomediastinum or subcutaneous emphysema.
- Post Dental Extraction: Another very rare cause, possibly due to air entering tissue planes and tracking.
- Following Arthroscopy of the Knee: Rarely, air used for distention during arthroscopy can track into the retroperitoneum and potentially mimic pneumoperitoneum.
- Intra-abdominal Sepsis by Gas-Forming Organisms: Infections caused by bacteria capable of producing gas, such as Klebsiella, Escherichia coli, Clostridium, Staphylococcus, Streptococcus, Candida, and Pseudomonas, can lead to pneumoperitoneum even in the absence of perforation. This is the mechanism in our case.
- Pneumatosis Coli: Air within the bowel wall itself, usually benign, but in severe cases, it can mimic free air or be associated with serious conditions like bowel ischemia.
- Vaginal Insufflation for Tubal Patency Test: Air introduced during procedures like hysterosalpingography can rarely track into the peritoneal cavity.
- Overlying Bowel Gas (Chilaiditi Syndrome): Interposition of the colon between the liver and diaphragm can mimic pneumoperitoneum on X-ray, but this is a positional anomaly, not true free air.
Pancreatic Abscess as a Rare Cause
In the presented case, the etiology of pneumoperitoneum was a ruptured pancreatic abscess, a particularly rare cause of air under the diaphragm. The abscess was caused by Klebsiella, a known gas-forming organism. These organisms utilize glucose fermentation, particularly the mixed acid fermentation pathway, which, under anaerobic conditions and low pH, can lead to the production of carbon dioxide and hydrogen gas. In diabetic patients, such as our patient, elevated blood glucose levels provide an abundant substrate for bacterial fermentation and gas production within an abscess cavity. Furthermore, diabetes-related microangiopathy and compromised immune function can hinder the clearance of metabolic byproducts, promoting gas accumulation within the infected pancreatic tissue.
Diagnostic Modalities and Considerations
While erect chest or abdominal X-rays are often the initial screening tool for pneumoperitoneum, detecting free air in 60-70% of cases of peritonitis, ultrasound offers improved sensitivity (85-100%) and specificity (84-100%). However, CT scanning of the abdomen is considered the gold standard for detecting even small amounts of free air (as low as 5cc) and can also identify the source of perforation or intra-abdominal pathology with greater accuracy. In cases of suspected pancreatic abscess, CT is invaluable in visualizing intra-pancreatic gas, gas within the portal vein, and the abscess itself. Despite its diagnostic superiority, CT scanning may not always be readily available or financially feasible, as in our patient’s case, highlighting the continued importance of clinical acumen and judicious use of available resources like ultrasound.
Pancreatic abscesses are a serious complication of acute pancreatitis, occurring in 5-9% of cases. They represent collections of pus and necrotic debris, often arising from the liquefaction of necrotic pancreatic and peripancreatic tissues or infection of pre-existing fluid collections. Immunocompromised individuals and those with chronic renal failure are at increased risk. While open surgical debridement remains a standard treatment, percutaneous and minimally invasive drainage approaches are increasingly utilized with success.
Conclusion
This case underscores the importance of considering a broad differential diagnosis when encountering air under the diaphragm. While hollow viscus perforation remains the most common cause, atypical presentations such as pancreatic abscess, particularly in the context of gas-forming bacterial infections, should be recognized. To the best of our knowledge, pancreatic abscess presenting as an extraintestinal source of gas under the diaphragm has been sparsely documented in English literature, highlighting the rarity and educational value of this case. A systematic approach to differential diagnosis, coupled with appropriate imaging modalities, is crucial for accurate diagnosis and optimal patient management in cases of pneumoperitoneum, especially when the clinical picture is not straightforward.
Conflict of interest
Dr Sreevathsa MR and Dr Khyati Melanta declare that they have no conflict of interest.
Funding
None.
Ethical approval
Not applicable.
Consent
Informed consent of patient for publishing case details and images have been taken.
Author contributions
Dr Sreevathsa M.R: Design, data collection, writing the paper, analysis.
Dr Khyati Melanta: data collection, writing.
Guarantor
Dr M.R. Sreevathsa.
Contributor Information
Maddibande Ramachar Sreevathsa, Email: [email protected].
Khyati Melanta, Email: [email protected].
