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Indications / Contraindications
Indications
- Lower GI hemorrhage (distal to ligament of Treitz) refractory to endoscopic management or in hemodynamically unstable patient
- Active extravasation on CTA (sensitivity ~79–85% for LGIB)
- Failed colonoscopy (blood obscuring view, inadequate prep, or endoscopist unable to achieve hemostasis)
- Hemodynamic instability requiring >5 units pRBC in 24h
- Causes: Diverticulosis (#1 — ~30%), hemorrhoids, ischemic colitis, angiodysplasia, post-polypectomy, IBD, tumor
- Key: Lower GI has LESS collateral supply than upper GI — ischemia risk is HIGHER. Superselective is mandatory.
Contraindications
- Absolute: None in life-threatening hemorrhage
- Relative: Severe contrast allergy (premedicate or CO2); Renal insufficiency (minimize contrast); Uncorrectable coagulopathy (correct while proceeding)
- Critical difference from upper GI: Do NOT empirically embolize in lower GI without angiographic visualization of bleeding — too high an ischemia risk without a confirmed target
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Pre-Procedure Checklist
Hemodynamic pathway decision: Stable → colonoscopy first (preferred); Unstable (SBP ≤90, >5 units pRBC) → CTA → IR directly. Do not delay IR for bowel prep in the unstable patient.
CTA angiography: Best localizes bleeding source (sensitivity 79–85%). Guides targeted selective catheterization. Identifies underlying pathology (diverticulum, AVM, tumor). Use as procedural roadmap.
Nuclear RBC scan (Tc-99m): More sensitive (~0.1 mL/min) but localizes poorly. Largely supplanted by CTA at most centers. May be useful for identifying intermittent bleeding prior to angiography.
Labs and resuscitation: CBC, PT/PTT/INR, BMP, type & cross. Transfusion threshold: maintain Hgb >7 g/dL (or >8 in CAD). Active resuscitation continues through procedure.
Consent: Colonic ischemia (most feared in lower GI), rebleeding, post-embolization syndrome, contrast nephropathy, access site complications.
Colonoscopy coordination: Plan for post-procedure colonoscopy at 24h to confirm hemostasis and assess mucosal viability.
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Relevant Anatomy
Colonic Vascular Supply
- SMA → right colon: Ileocolic (cecum/ascending), right colic, middle colic (transverse)
- IMA → left colon and rectum: Left colic (descending), sigmoid branches, superior rectal artery
- Rectum (dual supply): Superior rectal (from IMA) + middle/inferior rectal (from internal iliac)
- Vasa recta: End arteries supplying colonic wall from marginal artery (Drummond) — 1–3 cm straight vessels. Embolization at vasa recta level limits ischemia to <5 cm segment.
Critical Zones and Principles
- Watershed zones: Splenic flexure (middle colic ↔ left colic) and rectosigmoid — HIGHEST ischemia risk. Superselective only in these areas.
- Proximal SMA/IMA embolization = danger: Segmental ischemia or infarction risk. Always superselect.
- Small bowel: Jejunal and ileal branches from SMA. Rich marginal arcades → lower ischemia risk than colon
- Marginal artery of Drummond: Connects SMA and IMA territories along the mesenteric border — critical for collateral flow
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Technique
Default RadCall approach · share your own below
Supplies
Micropuncture kit
5 Fr sheath
Flush catheter (pigtail)
Selective catheter (Cobra / SH)
Microcatheter 2.4–2.7 Fr
0.014–0.018" microwire (hydrophilic)
Microcoils (0.018" pushable)
Gelfoam pledgets
Contrast + heparinized saline flush
3-way stopcocks
Steps
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Arterial access
Common femoral artery (CFA), 5 Fr sheath. Heparin bolus 3,000–5,000 units IV after access.
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Initial angiography — target CTA-based vessel
Based on CTA findings, target the most likely vessel first. CTA shows right colon bleeding → SMA first. Left colon/sigmoid → IMA first. This approach minimizes contrast use and procedure time.
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SMA angiogram
AP arteriogram. Selective branches: ileocolic (cecum/ascending colon), right colic, middle colic (transverse colon). Look for contrast extravasation or blush. Compare to CTA location.
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IMA angiogram
Catheter to IMA (L2–L3 level, anterior aorta). Branches: left colic (descending colon), sigmoid branches, superior rectal artery. AP arteriogram; oblique views may help for IMA branches.
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Superselective catheterization — CRITICAL
Advance microcatheter as far distally as possible — ideally to the level of the vasa recta directly adjacent to the bleeding point. Use CTA as roadmap for navigation. This step is non-negotiable in lower GI embolization.
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Confirm extravasation
Superselective injection confirms active bleed site. Always correlate position to CTA location before embolizing. Proximity to watershed zone increases scrutiny threshold.
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Embolization
Microcoils first choice — placed superselectively at vasa recta level. Gelfoam acceptable if microcatheter cannot reach vasa recta level. AVOID large particles (PVA ≥300 μm) in colon — unacceptable ischemia risk. In uncorrectable coagulopathy or non-focal bleeding: Gelfoam preferred over permanent occlusion.
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Post-embolization check
Full SMA and/or IMA arteriogram to confirm no residual extravasation and no non-target embolization. Evaluate the colonic segment supplied by embolized vessel — look for pruning or stasis indicating ischemia.
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Troubleshooting
Problem
Cannot localize on angiography despite active CTA bleed
Likely cause: Intermittent bleeding with cessation before angiography; contrast timing mismatch.
Next step: Use CTA as anatomic roadmap — superselect the vessel based on anatomy even without active extravasation. Provocative angiography (heparin, vasodilators, low-dose tPA) as last resort. Unlike upper GI, do NOT empirically embolize in lower GI without visualization.
Problem
Cannot advance microcatheter to vasa recta level
Likely cause: Tortuous mesenteric vessels, vessel spasm, or inadequate catheter support.
Next step: More proximal embolization (branch level) is acceptable but increases ischemia risk — document this decision. Hydrophilic microwire (Fathom, Synchro). Coaxial technique with larger support catheter. Accept higher-level embolization if unable to progress, but document rationale.
Problem
Post-embolization ischemic colitis
Likely cause: Inadequate collateral supply — most common with watershed zone embolization or proximal occlusion.
Next step: Abdominal pain + bloody diarrhea + peritoneal signs post-procedure = emergency. Surgical consultation immediately. CT abdomen/pelvis to assess extent of ischemia. Surgery for transmural infarction — IR cannot solve this problem.
Problem
Small bowel bleed (Dieulafoy, GAVE, angiodysplasia)
Likely cause: Aberrant or ectatic mucosal vessel — may be subtle on angiography.
Next step: Superselective embolization has lower ischemia risk in small bowel given rich arcades. Coils preferred. Coordinate post-procedure capsule endoscopy or push enteroscopy for definitive characterization and potential recurrence management.
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Complications
Primary Risks
- Colonic ischemia — 5–10% with proximal embolization; <1% with superselective vasa recta technique. Most feared complication. Can require colectomy.
- Rebleeding — ~20–30%; repeat embolization or surgery
- Non-target embolization — inadvertent occlusion of adjacent bowel segment
Secondary Risks
- Post-embolization syndrome — fever, leukocytosis, pain; usually mild; supportive care
- Access site hematoma — standard CFA complication; manual compression or closure device
- Contrast nephropathy — minimize contrast load; CO2 angiography for SMA/IMA assessment in renal insufficiency
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Post-Procedure Care
Monitoring
- ICU monitoring post-procedure
- Abdominal exams q6h for 24h — peritoneal signs or worsening pain = ischemia until proven otherwise → surgical consultation immediately
- Diet: NPO → clear liquids → advance per clinical trajectory
- Serial CBC q6–8h for first 24h
- Persistent/recurrent bleed: falling Hgb, return of hematochezia → repeat CTA → repeat embolization or surgery consult
Follow-up and Definitive Therapy
- Colonoscopy at 24h when safe — confirms hemostasis, evaluates mucosal viability, assesses for ischemia
- Transfusion threshold: Hgb >7 g/dL in most patients; >8 g/dL in CAD or ACS patients
- Diverticular disease: Consider elective colonic resection if recurrent episodes (>2 bleeding episodes)
- Surgical consultation on standby for failed embolization or ischemic complications
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Critical Pearls
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SUPERSELECTIVE IS EVERYTHING in lower GI: Colonic vasa recta are end arteries. Proximal embolization = segmental infarction. You must reach the vasa recta. This is non-negotiable.
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Do NOT empirically embolize in lower GI: Unlike upper GI where empiric left gastric embolization is reasonable, lower GI embolization without visible extravasation carries unacceptable ischemia risk. Wait and restudy.
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Diverticular bleed: Most common cause of LGIB. Bleeds are often profuse and sudden. Identify the actual diverticulum on angiography — don't just embolize the nearest vessel. CTA roadmap is essential.
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Watershed zones demand extreme caution: Splenic flexure (middle colic ↔ left colic junction) and rectosigmoid are most ischemia-vulnerable. If you must embolize here, vasa recta level only — no exceptions.
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Sigmoid/rectal bleeding: Dual supply via IMA (superior rectal) and internal iliac (middle/inferior rectal) — lower ischemia risk than colon. Important anatomic protection when embolizing this region.
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Angiodysplasia — consider endoscopy: Diffuse, non-targeted lesions. May require embolization of multiple points but colonoscopy with argon plasma coagulation (APC) is often better definitive therapy.
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Ischemia Risk by Location
| Location | Arterial Supply | Collateral | Ischemia Risk | Strategy |
|---|---|---|---|---|
| Cecum / Ascending | Ileocolic, R colic | SMA arcades, marginal a. | Low | More proximal embolization acceptable |
| Hepatic flexure | R colic, middle colic | SMA | Low–moderate | Superselect when possible |
| Transverse colon | Middle colic | Marginal artery | Moderate | Superselective preferred |
| Splenic flexure | Middle colic, L colic | Watershed! | HIGH | Vasa recta only |
| Descending / Sigmoid | L colic, sigmoid branches | Marginal artery | Moderate–high | Superselective mandatory |
| Rectosigmoid | Sigmoid, sup. rectal | Watershed! | HIGH | Superselective; consider rectal vasculature |
| Rectum | Sup. rectal + middle/inf. rectal | Internal iliac | Low | Dual supply protective |
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References & Resources
Primary sources · Key data · Related procedures
Key Guidelines
- ACR Appropriateness Criteria — Rectal Bleeding
- SIR Standards of Practice
- CIRSE Standards of Practice
Primary References
- Koh DC et al. Mesenteric embolization for lower gastrointestinal bleeding. Ann Acad Med Singapore. 2009;38(1):73-80.
- Bandi R et al. Superselective arterial embolization for the treatment of lower gastrointestinal hemorrhage. J Vasc Interv Radiol. 2001;12(12):1399-1405.
- Strate LL, Naumann CR. The role of colonoscopy and radiological procedures in the management of acute lower intestinal bleeding. Clin Gastroenterol Hepatol. 2010;8(4):333-343.