Interventional Radiology
Core framework
IR questions test indications, contraindications, technique steps, and complication recognition. Know the Seldinger technique (needle, wire, catheter, sheath) and the difference between diagnostic and embolic catheters. Vascular access: common femoral artery puncture at the mid-femoral head, well below the inferior epigastric artery origin and above the femoral bifurcation.
Embolization and oncology
Embolic agents: coils (permanent, large vessel), gelatin sponge (temporary, medium), polyvinyl alcohol particles (permanent, small vessel), and microspheres. Indications include GI bleeding, trauma, epistaxis (sphenopalatine), and tumor devascularization. TIPS reduces portosystemic pressure gradient; a target post-TIPS gradient is <12 mmHg, and complications include encephalopathy and shunt stenosis. Ablation (radiofrequency, microwave, cryo) is used for small HCC and renal and lung tumors; a 0.5–1 cm margin is desired.
Biliary and GU
Percutaneous transhepatic cholangiography is used when ERCP fails; know the risk of hemobilia and sepsis. Nephrostomy indications: obstruction with infection or failed retrograde access. Uterine artery embolization for fibroids uses particles, with ovarian failure as a rare complication.
Traps and rule of thumb
Traps: confusing a temporary agent (gelatin sponge) with permanent particles; forgetting to check coagulation and renal function before contrast; not recognizing postembolization syndrome (fever, pain, leukocytosis) as expected rather than infectious. Also know radiation protection: ALARA, pulsed fluoroscopy, last-image hold, and inverse-square dose falloff.
Rule of thumb: for GI bleeding, first localize with CT angiography if the patient is stable; angiography detects bleeding at roughly 0.5 mL/min, while a tagged red cell scan is more sensitive but less localizing.