What are push enteroscopy, enteroclysis, and Technetium (TC) labeled Red Blood Cell (RBC) scans?

Diagnostic Techniques for Small Bowel Evaluation

Push Enteroscopy

Push enteroscopy is an endoscopic procedure that allows visualization and intervention in the proximal small bowel beyond the reach of standard upper endoscopy, typically examining 50-120 cm of the jejunum beyond the ligament of Treitz. 1

• Technical aspects:

  • Utilizes a longer endoscope (200-250 cm) compared to standard upper endoscopes
  • May be performed with an overtube to reduce looping and increase insertion depth
  • Allows for direct visualization, biopsy, and therapeutic interventions (polypectomy, hemostasis, stricture dilation)
  • Average insertion depth is 90-113 cm past the ligament of Treitz 2

• Clinical applications:

  • Evaluation of obscure gastrointestinal bleeding with diagnostic yield of 50-64% 3, 2
  • Tissue sampling of small bowel lesions identified on other imaging modalities
  • Therapeutic interventions for accessible small bowel pathology
  • Should be reserved for when capsule endoscopy is unavailable or has failed to identify the source of bleeding 1

• Limitations:

  • Limited depth of insertion compared to device-assisted enteroscopy
  • Requires deep sedation or general anesthesia
  • Capsule endoscopy identifies bleeding sources more effectively (50% vs 24%) 1

Enteroclysis

Enteroclysis is a specialized radiographic technique for small bowel imaging that involves direct instillation of contrast material into the duodenum via a nasojejunal tube to achieve optimal small bowel distension. 1

• Technical aspects:

  • Requires placement of a nasojejunal tube under fluoroscopic guidance
  • Uses conventional X-ray equipment with digital fluoroscopy
  • May involve single contrast (barium) or double contrast (barium followed by air/methylcellulose)
  • Patient preparation includes fasting for at least 6 hours 1

• Clinical applications:

  • Detection of mucosal abnormalities including ulcerations and strictures
  • Identification of extramural complications such as internal fistulas
  • Has been largely replaced by cross-sectional imaging techniques (CT/MR enterography)

• Limitations:

  • Poor diagnostic yield (7%) compared to capsule endoscopy (30%) for obscure GI bleeding 1
  • Patient discomfort due to tube placement
  • Radiation exposure
  • Limited sensitivity for subtle mucosal lesions
  • Should not be considered a useful diagnostic tool in patients with obscure gastrointestinal bleeding 1

Technetium-99m Labeled RBC Scans

Technetium-99m labeled RBC scans are nuclear medicine studies that can detect active gastrointestinal bleeding at rates as low as 0.05-0.1 mL/min by tagging the patient's red blood cells with radioactive technetium. 1

• Technical aspects:

  • Involves in vivo labeling of patient's RBCs with technetium-99m
  • Imaging includes dynamic phase followed by static images at intervals
  • Modern techniques incorporate SPECT/CT for improved anatomical localization 1
  • Can detect slower bleeding rates than angiography (0.05-0.1 mL/min vs 0.5-1.0 mL/min) 1

• Clinical applications:

  • Detection and localization of active GI bleeding when endoscopy is negative
  • Particularly useful for intermittent bleeding
  • Can guide subsequent interventions (angiography, surgery)
  • Diagnostic yield of 69% for localizing obscure GI bleeding sources 4

• Limitations:

  • Limited anatomical resolution without SPECT/CT
  • Potential for incorrect localization (10-33% of cases) 1
  • Poor specificity for localization (33.3%) compared to CTA (90.9%) 1
  • No role when bleeding site has been positively identified by other methods 1
  • Planar-only radionuclide scans without SPECT/CT should not be used for small bowel evaluation due to lower accuracy in locating bleeding sites 1

Comparative Effectiveness

When evaluating the small bowel for obscure gastrointestinal bleeding:

1. Capsule endoscopy has the highest diagnostic yield (50-63%) and should be considered first-line for stable patients 1
2. CT enterography with neutral oral contrast offers excellent visualization of the small bowel wall and lumen, with sensitivity of 75-90% and specificity >90% for Crohn's disease 5
3. Push enteroscopy has lower diagnostic yield (24-28%) compared to capsule endoscopy but offers therapeutic capabilities 1
4. Tc-99m RBC scans can detect slower bleeding rates but have localization limitations unless SPECT/CT is used 1
5. Enteroclysis has poor diagnostic yield (7%) and has been largely replaced by cross-sectional imaging techniques 1

Common pitfalls:

• Relying on planar-only Tc-99m RBC scans without SPECT/CT for small bowel bleeding localization
• Using enteroclysis as first-line for obscure GI bleeding evaluation
• Performing push enteroscopy before capsule endoscopy in stable patients without obstruction
• Failing to consider CT enterography with neutral oral contrast when evaluating for inflammatory bowel disease