The authors discuss the different causes of ectopic gas with an etiopathogenic approach.Discuss common and uncommon causes of ectopic gas.

1- Spontaneous origin:

Gas can be spontaneously or incidentally depicted in daily radiologic practice without necessarily being related to iatrogenesis, trauma, malignancy, infection, or ischemic phenomena, such as in cholelithiasis or intervertebral disks.[2]

1.1 Spontaneous pneumomediastinum (SPM):

CT potentially allows differentiation of SPM from secondary pneumomediastinum, particularly when it is caused by traumatic tracheobronchial injury, esophageal rupture, or infectious mediastinitis, which are life-threatening causes of pneumomediastinum.[2]

Fig 2: Spontaneous pneumomediastinum is known as Hamman's syndrome. This condition is...

Fig 3: Air/gas spread to the upper limbs.

1.2 Vacuum disk phenomenon:

On imaging studies, a vacuum disc can be recognized as a lucency within either the intervertebral disc or a synovial joint as a direct product of the liberation of a gas consisting of 95% nitrogen and lesser amounts of oxygen and carbon dioxide into the disc as well as joint space.[5]

However, the presence of gas does not categorically imply merely degenerative disc disease, as other processes can lead to discs containing gas. Examples of other conditions with gas include: vertebral osteomyelitis, Schmorl node formation and spondylosis deformans.

Fig 4: Vacuum disk phenomenon.

1.3 Gas within Gallstones:

Gallstones, particularly soft ones (eg, cholesterol stones) may develop central fissures as they degenerate during the crystallization process.[Occasionally, nitrogen gas may collect in these fissures, causing a radiolucency that adopts a triradiate pattern.[2]

Fig 5: Gas within Gallstones.

2- Inflammatory conditions: 

2.1 Gastric ulcers: 

Peptic ulcers are mucosal breaks of 3 mm or greater and are common, occurring in about 10% of adults in Western countries. Gastric ulcers account for about one third of peptic ulcers, and duodenal ulcers account for the remainder. Because a small percentage (< 5%) of gastric ulcers are caused by ulcerated gastric carcinomas, all gastric ulcers must be carefully assessed to differentiate benign lesions from malignant lesions. With the decline of Helicobacter pylori infection, the detection of idiopathic peptic ulcer disease has become more frequent, making diagnosis and treatment more difficult.[5]

Fig 6: Gastric ulcer.

2.2 Vasculitis:

The symptoms of vasculitis depend on the particular blood vessels that are involved by the inflammatory process.

Fig 7: We report a 32 year old male admitted to a critical care unit for fever, lung...

Fig 8: We report a 32 year old male admitted to a critical care unit for fever, lung...

3-Infectious: 

Gas-forming infections represent potentially life-threatening conditions that require aggressive medical and often surgical management, as they tend to progress rapidly to sepsis in the absence of early therapeutic intervention.[2]

3.1 Emphysematous Infections:

3.1.1 Emphysematous pancreatitis.

Fig 9: Emphysematous pancreatitis.

3.1.2 Emphysematous cystitis.

Fig 10: Emphysematous cystitis.

3.1.3 Emphysematous cholecystitis and hepatitis.

Fig 11: Emphysematous cholecystitis and hepatitis.

3.1.4 Emphysematous pyelonephritis. Pyonephrosis.

Fig 12: Emphysematous pyelonephritis. Pyonephrosis.

3.1.5 Fournier gangrene.

Fig 13: Fournier gangrene.

Fig 14: Fournier gangrene.

3.2 Other causes:

3.2.1 Osteomyelitis- Pressure sores.

Fig 15: Osteomyelitis- Pressure sores.

3.2.2 Perforated Appendicitis-diverticulitis.

Fig 16: Perforated Appendicitis-diverticulitis.

3.3 Organisms:

The presence of abnormal gas in any part of the body should suggest the possibility of gas infection.

-Emphysematous cystitis or pyelonephritis – usually E. coli or Klebsiella.

-Emphysematous cholecystitis – 1/3 Clostridium perfringens, the rest are mostly E. coli or Klebsiella.

-Gas gangrene/ myonecrosis – Clostridium perfringens; C. septicum is associated with colon cancer (as is C. bovis).

-Vibrio vulnificans – salt water, bullous lesions, liver disease.

-Pneumocystis intestinalis = gas in the intestinal wall, seen in ischemic gut, COPD, necrotizing enterocolitis; associated with steroids and chemotherapy.

-Necrotizing fasciitis – I = polymicrobial, II = S. pyogenes – gas results from necrosis.

-Aeromonas hydrophila – associated with crocodile/ alligator bites and fish; bullous lesions, liver disease – mimics Vibro vulniicans.

-Clostridium sordelei – normal flora of female genital tract; associated with abortions.

4- Neoplastic:

Ectopic gas related to malignancy is usually the result of perforation or fistulization of a normal air-containing structure by a neoplastic mass. Radiologists should be aware of this condition, as most of the tumors causing it are malignant, which may have a deleterious effect on the patient’s prognosis.[2].

Acute bowel obstruction, perforation, ischemia, and intussusception are the most common bowel-related emergencies in cancer patients. Advanced gastrointestinal and gynecologic malignancies are the most frequent cause of malignant bowel obstruction.

Pathophysiologic events in acute bowel obstruction include intramural occlusion of the lumen because of malignancy within the wall, which causes poor motility and intestinal linitis plastica;intraluminal occlusion, which results from tumor growth within the bowel wall; and extrinsic luminal occlusion from serosal metastases.[7]

Fig 17: CT/MRI images obtained in a 68-year-old man who had undergone abdominoperineal...

Fig 18: Acute bowel obstruction, perforation, ischemia, and intussusception are the...

Fig 19: Tension pneumoperitoneum, a form of abdominal compartment syndrome, is an...

Fig 20: Neoplastic complications. Examples.

Fig 21: Neoplastic complications. Examples.

5- Ischemic:

Pneumatosis intestinalis is defined as the presence of gas within the wall of the gastrointestinal tract. Traditionally, pneumatosis has been reported as a sign of intestinal ischemia, requiring immediatesurgical exploration. However, new evidence indicates that pneumatosis might be benign, and early surgical intervention might be unnecessary and even harmful. Thus, radiology plays a central rolein helping diagnose clinically worrisome pneumatosis on the basis of certain alarm signs.[2]

Fig 22: Pneumatosis intestinalis: It is an imaging finding (not a definite diagnosis),...

Fig 23: Thrombosis of the celiac artery trunk is a rare cause of acute abdominal pain....

Fig 24: Location of pneumobilia and portal vein gas in the liver based on the direction...

6- Iatrogenic:

Iatrogenesis is one of the most frequent causes of ectopic gas in daily radiologic practice, and it is often related to the postoperative state. Other iatrogenic conditions associated with ectopic gas include tension pneumocephalus, air embolism, and gossypiboma.[2]

Fig 25: Duodenal perforations after endoscopic retrograde cholangiopancreatography...

Fig 26: Location of pneumobilia and portal vein gas in the liver based on the direction...

Fig 27: Iatrogenic causes. Examples.

Fig 28: Iatrogenic causes. Examples

Fig 29: Iatrogenic perforations due to enemas lead to adverse outcomes in elderly...

7- Trauma related:

Criminal events have grown exponentially over the past decade in Argentina as a product of a deep and sustained economic and social crisis.

The city of Rosario, located 300 km from the capital Buenos Aires, has been the epicenter of the well-known "balaceras" (shooting) related to the consolidation of drug trafficking in the most vulnerable neighborhoods of the city.

MDCT is an integral part of the evaluation for all patients with gunshot wounds who have no obvious clinical indications for laparotomy.

Fig 30: Criminal events have grown exponentially over the past decade in Argentina as a...