Interventional radiology Study Guide

📖 Core Concepts Interventional Radiology (IR) – Minimally‑invasive procedures performed under imaging guidance (fluoroscopy, CT, MRI, US) through tiny incisions or natural orifices. Seldinger Technique – Needle puncture → guidewire insertion → sheath placement → catheter advancement; the backbone of virtually every IR access. Imaging Guidance – Real‑time navigation (fluoro, US) vs. cross‑sectional planning (CT, MRI). Each modality has strengths: fluoro = continuous X‑ray, US = no radiation, CT = 3‑D detail, MRI = soft‑tissue contrast. Access Tools – Needle → guidewire → sheath → catheter; they maintain a safe, patent tract to the target. Embolization – Intentional occlusion of a vessel using coils, particles, glue, or plugs to stop bleeding or cut tumor blood supply. Balloon Angioplasty & Stenting – Balloon inflates to dilate a stenosis; a stent (bare‑metal, drug‑coated, or graft) scaffolds the vessel to stay open. Tumor Ablation – Energy‑based destruction (radiofrequency, microwave, cryo, HIFU) delivered percutaneously under image guidance. Hemostasis vs. Perfusion Balance – IR aims to stop unwanted bleeding while preserving flow to vital tissues; choice of embolic material size/viscosity reflects this balance. Venous Physiology – Low‑pressure system with valves; muscle pump and respiration drive flow back to the heart. --- 📌 Must Remember Key Benefits – Less trauma, lower infection risk, shorter stay, real‑time precision. Major Risks – Radiation exposure (cataracts, cancer), limited immediate access in emergencies. Imaging Modality Choice Fluoro → vascular navigation. CT → 3‑D road‑mapping, bone detail. MRI → soft‑tissue, no ionizing radiation. US → bedside, vascular/abdominal, no radiation. Embolic Agent Selection Coils – Precise, permanent occlusion of larger vessels. Particles (PVA, gelatin‑foam) – Small‑vessel occlusion, temporary (gel‑foam) vs. permanent (PVA). Glue (cyanoacrylate) – Rapid polymerization, useful for high‑flow lesions. Stent Types Bare‑metal – Simple scaffold. Drug‑eluting – Releases antiproliferative drug to reduce restenosis. Stent‑graft – Fabric‑covered, for aneurysm exclusion or arterial bleeding. Ablation Temperatures RF: 60–100 °C (coagulative necrosis). Microwave: >150 °C (faster, larger zones). Cryo: −40 °C to −80 °C (ice ball visible). Peripheral Artery Disease (PAD) Clues – Claudication (exercise‑induced leg pain), ankle‑brachial index < 0.9. Critical Limb Ischemia – Rest pain, ulcer/gangrene, requires urgent revascularization. Aortic Dissection Classification – Stanford A = ascending (surgical); Stanford B = distal (medical ± endovascular). --- 🔄 Key Processes Seldinger Access Puncture skin & vessel with needle → confirm blood return. Insert guidewire through needle → remove needle. Advance sheath over wire → remove wire. Pass catheter/sheath‑based device to target. Digital Subtraction Angiography (DSA) Acquire non‑contrast “mask” image. Inject contrast → acquire series. Subtract mask → highlight vessels alone. Embolization Workflow Identify bleeding/tumor feeder via angiography. Choose embolic (size, permanence). Deploy under fluoroscopy; confirm stasis. Balloon Angioplasty & Stenting Cross lesion with guidewire & catheter. Inflate balloon (usually 6–12 atm) to dilate. Deflate, remove balloon; assess residual stenosis. If ≥ 30 % residual → place stent. Tumor Ablation (Microwave example) Plan needle path with CT/US. Insert probe → verify tip position. Deliver microwave energy (typically 30–60 W for 5–10 min). Monitor ablation zone; ensure > 5 mm margin. Dialysis AVF/Graft Intervention Perform fistulogram → locate stenosis. Balloon angioplasty → restore lumen. Consider stent if elastic recoil > 30 %. --- 🔍 Key Comparisons Fluoroscopy vs. CT Guidance Fluoro: real‑time, lower radiation dose per frame, excellent for vascular navigation. CT: cross‑sectional detail, 3‑D planning, higher radiation per study, slower. Coils vs. Particles (Embolization) Coils: larger vessels, permanent, visible on fluoroscopy. Particles: small distal vessels, can be temporary (gel‑foam) or permanent (PVA). Drug‑Coated Balloon vs. Plain Balloon DCB: delivers antiproliferative drug, reduces restenosis. Plain: mechanical dilation only; higher restenosis risk. Radiofrequency vs. Microwave Ablation RF: heat limited by tissue impedance, slower, single probe typical. Microwave: higher temps, less impedance limitation, can use multiple probes. Endovascular Stent‑Graft vs. Surgical Bypass (Aneurysm) Stent‑graft: minimally invasive, quicker recovery, limited by anatomy. Bypass: open surgery, more durable in hostile anatomy, higher morbidity. --- ⚠️ Common Misunderstandings “All embolizations stop bleeding permanently.” Some agents (gelatin‑foam) are absorbable; re‑bleeding can occur. “Radiation dose is negligible in IR.” Cumulative exposure can cause cataracts and increase cancer risk; shielding and low‑dose protocols are essential. “A stent eliminates need for follow‑up.” In‑stent restenosis can occur; imaging surveillance is required. “Cryoablation is only for bone lesions.” It’s also used in kidney, liver, and prostate tumors; the visible ice ball aids safety. “All PAD patients need angioplasty.” First‑line is lifestyle modification & meds; intervention reserved for refractory symptoms. --- 🧠 Mental Models / Intuition “Road‑Map Model” – Visualize the vessel as a road; the guidewire is a car, the sheath is a tunnel, and the catheter is the delivery truck. Keeps the sequence logical. “Size‑Matters Rule” – Larger embolic agents occlude proximally; smaller agents travel distally. Match agent size to target vessel diameter. “Temperature Gradient” – For ablation, think of the probe as a heat (or cold) source; the zone of necrosis expands outward until the temperature falls below the cytotoxic threshold. “Pressure‑Flow Balance” – In hemorrhage control, you want enough embolic material to raise downstream resistance (stop flow) without compromising adjacent perfusion. --- 🚩 Exceptions & Edge Cases Radiation‑Induced Cataracts – Occur with cumulative eye dose > 2 Sv; use lead glasses and limit fluoroscopy time. High‑Flow AV Shunts – Coils may migrate; consider vascular plugs or covered stents. Renal Insufficiency – Iodinated contrast can worsen kidney function; use CO₂ angiography or MR‑angiography when possible. Pseudoaneurysm – Small (< 2 cm) can be thrombin‑injected percutaneously; infected ones need surgical excision. Stanford B Dissection with Organ Ischemia – Though usually managed medically, endovascular fenestration or stent‑graft is indicated when branch vessels are compromised. --- 📍 When to Use Which Choose Imaging Modality Real‑time needle placement → US or fluoroscopy. Complex 3‑D anatomy (e.g., hepatic tumors) → CT. Soft‑tissue contrast needed (e.g., spinal lesions) → MRI. Select Embolic Material Large arterial bleed → coils or vascular plug. Diffuse tumor perfusion → particles or drug‑eluting beads. Rapid, high‑flow bleeding → glue (cyanoacrylate). Stent vs. Balloon Alone Elastic recoil > 30 % after balloon → stent. Vessel < 4 mm, high restenosis risk → drug‑eluting stent. Ablation Technique Small (< 3 cm) liver lesion → RF or microwave. Lesion near heat‑sensitive structures → cryo (visible ice ball). Bone pain palliation → microwave or RF with cementoplasty. Dialysis Access Intervention Stenosis without thrombosis → balloon angioplasty ± stent. Thrombosed fistula → thrombectomy, then angioplasty. --- 👀 Patterns to Recognize “Triphasic Contrast Curve” on hepatic angiography → suggests hypervascular tumor → candidate for chemo‑embolization. “Wedge‑Shaped Perfusion Defect” on CT after embolization → successful target vessel occlusion. “Ring‑Enhancement” on post‑ablation CT → expected inflammatory rim; larger than 1 cm may indicate residual tumor. “Delayed Enhancement” on MRI after TIPS → indicates shunt patency. “Collateral Vessel Recruitment” on chronic PAD angiograms → may guide distal bypass planning. --- 🗂️ Exam Traps Distractor: “All aneurysms are treated with open surgery.” Why wrong: Endovascular stent‑grafts are first‑line for many abdominal/thoracic aneurysms. Distractor: “Coils are the best choice for embolizing a high‑flow arteriovenous malformation.” Why wrong: High flow can displace coils; liquid embolics (glue, Onyx) are preferred. Distractor: “Microwave ablation always requires general anesthesia.” Why wrong: Many procedures are done under moderate sedation; anesthesia choice depends on patient and location. Distractor: “All peripheral arterial disease patients need stents.” Why wrong: First‑line is lifestyle and medication; stents reserved for refractory lesions. Distractor: “CT‑guided biopsy has no radiation risk.” Why wrong: CT uses ionizing radiation; dose‑saving techniques are essential. ---