Endoscopic Capsule (Capsule Endoscopy)
Capsule endoscopy is a wireless, pill-sized camera (measuring 26 × 11 mm) that is swallowed and travels through the gastrointestinal tract via intrinsic peristalsis, continuously capturing and transmitting images to an external data recorder for subsequent review by a trained gastroenterologist. 1
Technical Components and Mechanism
The capsule endoscope contains the following integrated components 1:
- Video imaging chip for capturing mucosal images
- Illuminating diode system for visualization
- Two batteries providing power (newer generations last >12 hours vs. 8 hours in first-generation devices) 1
- Radio transmitter for wireless relay of digital data to an externally worn receiver and sensor array
The patient wears a data recorder during the examination, and after completion (typically 8-12 hours), images are downloaded to a workstation for interpretation 1.
Primary Clinical Applications
Small Bowel Evaluation
Capsule endoscopy is the diagnostic procedure of choice for suspected mucosal lesions in the small bowel, which represents approximately 75% of the GI tract length and is largely inaccessible to conventional endoscopy. 1, 2
The most common indications include 1, 3:
- Obscure gastrointestinal bleeding (66% of all capsule endoscopy procedures) - should be performed as soon as possible after negative esophagogastroduodenoscopy and colonoscopy 1, 2
- Suspected or known Crohn's disease (10.4% of procedures) - particularly when ileocolonoscopy and cross-sectional imaging are negative or equivocal 1
- Small bowel neoplasms - especially important in patients younger than 50 years with obscure bleeding 2
- Iron-deficiency anemia with negative conventional workup (selected patients only) 1
Specific Pathology Detection
Capsule endoscopy identifies 2, 3:
- Angiectasias/arteriovenous malformations (most common finding, accounting for up to 80% of obscure bleeding cases and 50% of all OGIB findings)
- NSAID-induced small bowel ulcerations invisible to conventional endoscopy
- Crohn's disease involving jejunum and mid-small bowel beyond reach of ileocolonoscopy
- Small bowel tumors at early stages
- Dieulafoy's lesions in younger patients
Patient Preparation and Procedure
Pre-Procedure Requirements
Patients must 1:
- Fast for at least 12 hours prior to capsule ingestion
- Undergo bowel preparation (recommended to improve visualization and diagnostic yield) - polyethylene glycol in half dose (1 L), low volume (2 L), or high volume (4 L) has shown benefit 1
- Take clear liquids after 2 hours and food/medications after 4 hours following capsule ingestion 1
Special Populations
For patients with dysphagia, anatomical abnormalities, or gastroparesis, endoscopic delivery of the capsule can be performed 4:
- EGD with overtube placement
- Foreign body net retrieval device grasps activated capsule
- Capsule released in duodenum under direct visualization
For patients with poor GI motility or chronic narcotic use, confirm capsule reaches small bowel within 1 hour and continue study to full battery life 1.
Diagnostic Performance
Detection and Completion Rates
The pooled performance metrics are 3:
- Overall detection rate: 59.4%
- OGIB detection rate: 60.5%
- Crohn's disease detection rate: 55.3%
- Completion rate: 83.5% (capsule reaches cecum before battery expires)
Capsule endoscopy has greater sensitivity for mucosal small bowel Crohn's disease than radiological imaging techniques and should be performed when inflammatory small bowel disease is suspected despite normal or equivocal cross-sectional imaging 1.
Risks and Contraindications
Capsule Retention
The primary complication is capsule retention (capsule remaining in digestive tract for minimum 2 weeks), with pooled retention rates of 1, 3:
- 1.4% overall
- 1.2% in OGIB
- 2.6% in Crohn's disease
- 0-1.6% in suspected IBD
- 5.2-13% in known IBD
Risk Stratification for Retention
In patients with obstructive symptoms, known stricturing Crohn's disease, or imaging suggesting narrowing, cross-sectional imaging should be performed before capsule endoscopy 1. Risk factors for retention include 1:
- Known Crohn's disease with strictures
- Pelvic or abdominal radiation history
- Suspected tumors
- History of small bowel resection
- Chronic NSAID use
When retention risk is high, patency capsule should precede capsule endoscopy (risk of retention after successful patency capsule passage: 2.7%) 1.
Other Considerations
- Cardiac pacemakers: Previously considered a contraindication, but studies show no interference between pacemakers and capsule endoscopy 5
- Incomplete examinations: Occur in 20% overall, 12% in Crohn's disease patients 1
- Minor mucosal abnormalities: Can be seen in normal individuals, particularly with recent NSAID use; validated diagnostic criteria are still in development 1
Training and Interpretation Requirements
Capsule endoscopy should be performed and interpreted by a gastroenterologist experienced in conducting, interpreting, and reporting capsule endoscopy procedures 1. For IBD patients specifically, evaluation should be by gastroenterologists with experience in both conventional endoscopy and clinical management of IBD 1.
Limitations
Current capsule endoscopy cannot 6:
- Obtain tissue biopsies
- Perform therapeutic interventions
- Provide ideal images of esophagus, stomach, and colon (small bowel capsule) 1
The combination of capsule endoscopy and device-assisted enteroscopy (such as double-balloon enteroscopy) represents the optimal strategy for management of obscure GI bleeding, as device-assisted enteroscopy can retrieve retained capsules and perform therapeutic interventions 6.