Gastric Air on KUB: Diagnostic Significance
Gastric air on a Kidney, Ureter, Bladder (KUB) X-ray can indicate various conditions including gastric distention, gastroesophageal reflux disease (GERD), or potentially more serious conditions such as bowel obstruction or perforation, depending on the pattern and associated findings.
Normal vs. Abnormal Gastric Air
- Normal gastric air bubble is present in approximately 70% of normal chest and abdominal radiographs 1
- The form of the gastric air bubble can be classified into different types: dome-type, irregular-type, stomach-type, and undetected-type 1
- Stomach-type gastric air bubbles are most frequently associated with GERD symptoms 1
Pathological Significance of Gastric Air
- Presence of air in the esophagus, especially in the middle and lower parts, can suggest a diagnosis of GERD 2
- Air-fluid levels within a gastric ulcer are statistically more common in benign ulcers than in malignant ulcers, though this sign alone is not definitive for determining benignancy 3
- Gastric air with air-fluid levels may be seen in cases of gastritis or peptic ulcer disease (PUD) 2
Concerning Findings Associated with Gastric Air
- Extraluminal gas (97%), fluid or fat stranding along the gastroduodenal region (89%), and wall thickening (72%) are features associated with gastroduodenal perforation 2
- Free intraperitoneal air with gastric air may indicate perforation, which can be detected on KUB but is more sensitively identified on CT 2, 4
- Air-fluid levels of differential height in the same small-bowel loop and a mean air-fluid level width ≥25 mm on upright abdominal radiographs are highly predictive of high-grade or complete small bowel obstruction 5
Limitations of KUB for Diagnosis
- Plain X-rays, including KUB, have limited sensitivity (approximately 70%) for detecting bowel obstruction 2
- CT is superior to plain radiography for detecting air-fluid levels and associated complications such as perforation, with approximately 90% accuracy in predicting strangulation and need for urgent surgery 2
- KUB alone cannot reliably differentiate between various causes of abnormal gastric air patterns 6
When to Consider Additional Imaging
- If perforation is suspected based on gastric air patterns on KUB, CT with contrast enhancement should be performed 2
- For suspected bowel obstruction with gastric air distention, CT scan is the preferred imaging technique to assess the need for urgent surgery 2
- Water-soluble contrast studies may be useful when gastric air patterns suggest possible obstruction 2
Clinical Correlation
- Laboratory tests including white blood cell count and C-reactive protein should be performed when abnormal gastric air patterns suggest possible perforation or inflammation 2
- Patients with abnormal gastric air patterns and signs of peritonitis require immediate surgical intervention 7
- Small amounts of free air visible on CT but not on plain radiography may occur after procedures like endoscopic submucosal dissection without requiring surgical intervention 8