Imaging for Swallowed Foreign Body in the Abdomen
Order plain radiographs (anteroposterior and lateral views of chest, abdomen, and pelvis) as the initial imaging study, but proceed directly to CT scan if the patient is symptomatic, has high clinical suspicion, or if plain films are negative but concern persists. 1, 2
Initial Imaging Approach
Plain radiography is the first-line imaging modality for suspected foreign body ingestion, but it has significant limitations that must be understood upfront. 1, 3, 4
Critical Limitations of Plain X-rays:
- False-negative rates reach 47% for esophageal foreign bodies overall 2
- Up to 85% false-negative rate for food bolus, fish bones, chicken bones, and non-radiopaque objects 2
- Glass fragments, wooden objects (like chopsticks), and plastic materials are frequently missed 5, 6
- A negative X-ray does NOT rule out foreign body ingestion 2, 6
When Plain Films Are Useful:
- Identifying radiopaque objects (most metals, some glass) 1, 3
- Determining object shape, size, and location 1
- Detecting pneumoperitoneum (free air indicating perforation) 1
- Assessing for bowel obstruction patterns 7
When to Proceed Directly to CT Scan
CT scan should be performed without delay in the following scenarios:
Absolute Indications for CT:
- Any symptomatic patient despite negative X-ray 2, 6
- Suspected perforation (fever, persistent chest/abdominal pain, peritoneal signs) 1, 2
- Persistent symptoms for >24-48 hours 2
- High clinical suspicion with negative plain films 2, 6
- Known ingestion of non-radiopaque objects (wood, plastic, fish bones) 2, 6
CT Performance Characteristics:
- 90-100% sensitivity for detecting foreign bodies 2
- 93.7-100% specificity 2
- Superior for locating non-radiopaque objects 2, 7
- Essential for evaluating complications (perforation, abscess, obstruction) 2, 7
- Best modality for assessing extent of contamination and mediastinal involvement 8
Imaging Protocol Specifications
For Plain Radiographs:
- Obtain lateral AND anteroposterior views of chest, abdomen, and pelvis 1
- Include chest films to assess for pneumomediastinum or pneumothorax 1
For CT Scan:
- Use contrast-enhanced CT for suspected perforation in hemodynamically stable patients 1
- Use non-contrast CT for suspected drug packet concealment (contrast obscures packets) 9
- Multiplanar reconstruction improves detection 7
Clinical Decision Algorithm
Step 1: Obtain plain radiographs first
- If radiopaque foreign body clearly visualized AND patient asymptomatic → proceed based on object type and location 3, 4
Step 2: Proceed to CT if:
- Plain films negative but patient symptomatic 2, 6
- Suspected non-radiopaque object (fish bone, wood, plastic) 2, 6
- Any signs of perforation or obstruction 1, 2
- Persistent symptoms >24 hours 2
Step 3: Consider endoscopy timing based on findings:
- Emergent endoscopy (within 2-6 hours): Complete esophageal obstruction, sharp-pointed objects, button batteries, magnets 2
- Urgent endoscopy (within 24 hours): Other esophageal foreign bodies, persistent symptoms despite imaging 2
Common Pitfalls to Avoid
Never rely solely on negative plain films to exclude foreign body ingestion - this is the most dangerous error, as demonstrated by a case of duodenal perforation occurring 9 months after chopstick ingestion that was missed on initial X-ray. 6
Do not delay CT imaging in symptomatic patients - waiting for "serial X-rays" in a patient with persistent pain can miss early perforation. 2, 6
Avoid contrast-enhanced CT if drug packet concealment is suspected - contrast obscures the packets and reduces detection sensitivity. 9
Do not perform digital rectal examination before imaging if anorectal foreign body suspected - obtain X-ray first to prevent accidental injury from sharp objects. 1
Laboratory Workup
If perforation is suspected or patient requires intervention, obtain: 2
- Complete blood count (CBC)
- C-reactive protein (CRP)
- Serum creatinine
- Blood gas analysis (lactate, base excess)
- Inflammatory markers (procalcitonin if available)
Special Considerations
Hemodynamically unstable patients: Do not delay surgical treatment to perform imaging investigations. 1
Location matters: The ileum is the most common site for retained foreign bodies in the gastrointestinal tract (29% of cases), followed by the stomach. 7