GI Studies
41 Contrast Enema
Anatomy
- Cecum (large blind pouch below ileocecal valve)
- Appendix (vermiform process) (worm-like extension from cecum)
- Ascending colon
- Right colic (hepatic) flexure
- Transverse colon
- Left colic (splenic) flexure
- Descending colon
- Sigmoid colon
- Rectum
- Anus
🔑 Key Differentiators of Large vs Small Intestine:
- Larger internal diameter
- Three longitudinal muscle bands (taeniae coli) → create pouches called haustra
- Positioned along the periphery of the abdomen (vs. small bowel centrally located)
Indications, Contraindications, and Patient Preparation
Indications
- Colitis (inflammation of colon, causes include infection, diet, stress)
- Diverticulitis/diverticula (outpouchings of mucosa)
- Neoplasms (colon cancer → “apple-core” lesions)
- Volvulus (twisting of bowel)
- Intussusception (telescoping, common in infants)
- Appendicitis (clinical suspicion; appendix demonstrated in many cases)
Contraindications
- Suspected bowel perforation (use water-soluble iodinated contrast instead of barium)
- Recent colonoscopy with biopsy (risk of perforation)
- Severe diarrhea, gross bleeding, or acute appendicitis (contraindicated for prep)
Patient Preparation
- Low-residue diet 1–2 days before exam
- Laxative afternoon before exam (irritant or saline type)
- NPO after midnight
- No laxatives for patients with: severe diarrhea, obstruction, gross bleeding, or appendicitis
- Occasional cleansing enema as alternative prep
Projections
PA or AP Abdomen
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine (AP) or prone (PA)
- CR: Perpendicular to IR at level of iliac crest
- Pt. Instructions: Suspend respiration on expiration
Evaluation Criteria
- Entire large intestine included
- No rotation (iliac wings symmetric, spine midline)
Anterior Obliques (RAO / LAO)
CR Location & Positioning
- SID: 40 inches
- Patient position: 35–45° oblique
- CR: Perpendicular to IR, centered at level of iliac crest, 1″ lateral to midsagittal plane
- Pt. Instructions: Suspend respiration on expiration
Evaluation Criteria
- RAO → Right colic (hepatic) flexure open
- LAO → Left colic (splenic) flexure open
- Entire colon included
Posterior Obliques (RPO / LPO)
CR Location & Positioning
- Same as anterior obliques
- RPO opens left colic (splenic) flexure
- LPO opens right colic (hepatic) flexure
Evaluation Criteria
- Correct flexure demonstrated depending on position
- Entire colon included
Left Lateral Rectum
CR Location & Positioning
- SID: 40 inches
- Patient position: Left lateral
- CR: Perpendicular, directed to midaxillary line at level of ASIS
- Pt. Instructions: Suspend respiration
Evaluation Criteria
- Rectum and distal sigmoid well demonstrated
- No rotation
PA Axial (Billings)
CR Location & Positioning
- SID: 40 inches
- Patient position: Prone
- CR: Angled 30–40° caudad, centered to ASIS, exiting at level of pubic symphysis
- Pt. Instructions: Suspend respiration
Evaluation Criteria
- Rectosigmoid area elongated
- Pelvis not rotated
AP Axial (Billings)
CR Location & Positioning
- SID: 40 inches
- Patient position: Supine
- CR: Angled 30–40° cephalad, entering 2″ below ASIS at midline
- Pt. Instructions: Suspend respiration
Evaluation Criteria
- Rectosigmoid area elongated
- Pelvis not rotated
Procedure Adaptation
- Double-contrast studies (air contrast) → enhance mucosal detail, especially for polyps or early neoplasms.
- Water-soluble iodinated contrast → used if perforation or recent biopsy suspected.
- Pediatrics → intussusception can sometimes be reduced during BE.
- Geriatrics → may require slower filling and extra care with balloon inflation.
- Bag height → must not exceed 24 inches above the table to avoid excessive pressure.
Exposure Factors & Technical Considerations
- SID: 40 inches
- kVp: 100–125 (single contrast); 90–100 (double contrast)
- mAs: Short exposure times, use fluoroscopy to monitor filling
- Contrast:
- Single contrast → thin barium sulfate
- Double contrast → high-density barium + room air
- Water-soluble iodinated contrast → suspected perforation cases
- Collimation: Large field to include entire colon
- Shielding: Gonadal shielding where possible
Hows & Whys of Contrast Enemas
Anatomy & Physiology
- Which posterior oblique opens the right colic flexure?
LPO. - Which anterior oblique opens the right colic flexure?
RAO. - Which posterior oblique opens the left colic flexure?
RPO. - Which anterior oblique opens the left colic flexure?
LAO.
Contrast & Technique
- Why should exposures of the abdomen be made on expiration?
Expiration spreads out the abdominal organs, reducing overlap. - How do you separate the loops of bowel in the sigmoid colon?
Angle the tube 30–40° (AP or PA axial projections). - Why is double contrast often preferred?
It highlights mucosal detail and improves detection of small polyps and early cancers. - Why must the enema bag not exceed 24″ above the table?
To prevent excessive pressure that could cause overfilling or perforation.
Clinical & Safety Considerations
- Why use water-soluble iodinated contrast if perforation is suspected?
Because barium leakage into the peritoneum requires surgical removal; iodinated contrast can be absorbed/excreted safely. - Why must the radiologist be informed of recent colonoscopy with biopsy?
Because the bowel wall may be weakened and at higher risk of perforation. - Why is the Sims position used for tip insertion?
It relaxes the abdominal muscles and provides easier access for rectal insertion.