Description

• Air in the wall of the small or large intestine
• Can occur in a variety of clinical settings, ranging from benign to life-threatening
• Gas can be located in the mucosa, submucosa, and/or serosa.
• Pneumatosis intestinalis (PI) is a radiographic sign not a disease.
• Most commonly an incidental finding in adults
• Most patients are asymptomatic.
• Subdivided into two groups: (i) primary PI (15% of cases): Intramural gas is cystic and benign in nature; (ii) secondary PI (85% of cases): Gas accumulates as linear collections and reflects a pathologic condition often attributed to endoscopic procedures, immunologic disturbances, bowel mucosal disruptions, and intra-abdominal pathologies.
• Pseudonyms
  • Pneumatosis cystoides intestinalis
  • Cystic lymphopneumatosis
  • Intestinal emphysema
  • Intramural gas

Pediatric Considerations
PI is often found as a manifestation of fulminant, acute necrotizing enterocolitis (NEC) associated with prematurity and frequently leads to bowel infarction, perforation, and high mortality.

Epidemiology

• Bimodal distribution with peaks in premature infants and adults 41 to 50 years old
• Studies suggest a male-to-female predominance with ranges reported from 2:1 to 5:1.

Incidence
3/10,000 individuals (adult autopsy studies)

Prevalence
No population-based studies provide prevalence data.

Etiology and Pathophysiology

• Etiology is unknown but likely multifactorial. Several hypotheses have been proposed.
  • Mechanical theory: Gas is transmitted through a mucosal defect in the GI tract so that air dissects between tissue layers of the bowel wall. Peristalsis propagates gas to distant sites.
  • Bacterial theories
    • Bacteria (such as Escherichia coli and clostridia) enter the bowel wall through mucosal defects and produce gas.
    • Intraluminal bacterial overgrowth of fermenting bacteria leads to hydrogen gas accumulation, diffusion through the bowel wall, and intraluminal air trapping.
  • Pulmonary theory: In patients with chronic bronchitis, asthma, or emphysema, alveoli rupture and microscopic air enter the mediastinal space traveling along the great vessels into the retroperitoneum. Air tracks along the mesentery until it reaches the bowel and accumulates.
• An inflammatory reaction can occur as air is surrounded by histiocytes and macrophages. Over time, a histiocytic border with fibrosis creates air cysts within the bowel wall.

Genetics
No clear genetic linkage; PI in small numbers of families

Risk Factors

• Prematurity
• Male
• Medications such as lactulose, high-dose steroids, α-glucosidase inhibitors for diabetes mellitus type 2 (acarbose and miglitol), and chemotherapy agents (specifically daunorubicin, cytosine arabinoside, 5-fluorouracil, bevacizumab, sunitinib, and methotrexate)
• Organ transplantation
• Recent endoscopy, sigmoidoscopy, ERCP, or colonoscopy
• Immunosuppression
• Exposure to trichloroethylene
• Administration of infant formula; lack of administration of breast milk
• Secondary PI: hypotension or vasopressor use, peritonitis, lactate level >2 mmol/L, acute renal failure, and active mechanical ventilation

Commonly Associated Conditions

• NEC
• Peptic ulcer disease
• Asthma; pulmonary fibrosis; chronic obstructive pulmonary disease; cystic fibrosis
• Chronic hemodialysis
• AIDS
• Graft-versus-host disease
• Inflammatory bowel disease
• Intestinal tuberculosis
• Gastric cancer
• Scleroderma
• Blunt abdominal trauma
• Pseudomembranous colitis (Clostridium difficile infection)
• Diverticulitis
• Vascular disease