6.3 Scenario Practice for Ultrasound-Guided Procedures (7%)

6.3 Scenario Practice for Ultrasound-Guided Procedures (7%)

Scenario questions hand you a duplex finding and ask for the next action. Use a fixed reading order: setting → finding → threshold → decision.

Carotid endarterectomy completion study

After carotid endarterectomy (CEA), intraoperative duplex checks the repair before the wound is closed. The technologist looks for technical defects — an intimal flap, retained thrombus, a kink, or residual stenosis — because all are correctable on the table but become a stroke risk once closed.

Contrast-enhanced ultrasound (CEUS)

Microbubble contrast agents are pure intravascular tracers. They improve flow visualization in technically difficult patients, sharpen detection of slow flow, and are a leading tool for finding and classifying endoleaks after EVAR (endovascular aneurysm repair). Key safety facts the exam likes: microbubbles are not nephrotoxic (unlike iodinated CT contrast), involve no ionizing radiation, and are cleared via respiration. Contraindications include known right-to-left cardiac shunt and prior agent hypersensitivity.

Pseudoaneurysm triage scenarios

Walk the decision tree:

• Small (<2 cm), stable, off anticoagulation: observation or compression — many small PSAs thrombose spontaneously.
• Larger sac or patient anticoagulated: thrombin injection is first-line.
• Limb ischemia, infection, skin necrosis, rapid expansion, or very wide neck: surgical repair — minimally invasive methods are unsafe.

Worked example

A patient 6 hours post-catheterization on therapeutic heparin has a 3.5 cm groin PSA with a 4 mm neck, intact distal pulses, no skin changes. The decision driver is anticoagulation + sac >2 cm, both of which sink compression success. The defensible choice is ultrasound-guided thrombin injection, placing the needle in the sac body away from the neck, then re-scanning to confirm no residual sac flow and a patent parent artery. Surgery is not yet indicated because there is no ischemia, infection, or rapid expansion.

Endoleak scenarios after EVAR

A recurring scenario type asks you to interpret flow inside an aneurysm sac that has been excluded by a stent graft. Persistent flow within the sac outside the graft is an endoleak, and contrast-enhanced ultrasound is excellent at finding it and timing its appearance:

A growing sac with a high-pressure type I or III leak is urgent; a type II leak with a stable sac is often watched. The exam wants you to connect the flow location and timing to the leak type and to recognize that sac enlargement is the danger signal regardless of type.

How to break a two-answer tie

When two options look defensible, return to the cue the stem emphasized. If it stresses anticoagulation or a large sac, the tie usually breaks toward thrombin over compression. If it stresses ischemia, infection, or rapid expansion, it breaks toward surgery. If it stresses a post-CEA velocity number, compare it to the 150 cm/s and ICA/CCA >3.0 thresholds before deciding revise-versus-accept. If it stresses renal function or radiation concern, the contrast comparison favors microbubble ultrasound over CT angiography. Naming the cue out loud forces you to choose for a reason rather than by familiarity.

AV fistula versus pseudoaneurysm scenarios

A common paired scenario asks you to separate the two classic access complications. Both follow catheterization, both sit near the groin, but their flow stories differ completely. The fistula is an artery-to-vein shortcut: spectral Doppler in the feeding artery becomes low-resistance with high diastolic flow, the draining vein becomes pulsatile and arterialized, and color shows perivascular tissue vibration. The pseudoaneurysm is a blind sac: yin-yang swirling inside and to-and-fro at the neck.

If a stem describes "arterialized venous flow" or "continuous high diastolic signal," choose fistula; if it describes "swirling sac" or "forward-and-back neck flow," choose pseudoaneurysm. Many fistulas with small shunts are observed; symptomatic or high-flow fistulas may need endovascular or surgical closure.

Worked CEA example

Intraoperative completion duplex after a left carotid endarterectomy shows a mobile echogenic structure at the distal endarterectomy site with a focal PSV of 190 cm/s and post-stenotic turbulence. The decision driver is a velocity above the 150 cm/s revision threshold combined with a visible intimal flap. The defensible action is to revise the repair before closure — re-explore, remove the flap or thrombus, and re-image to confirm a normalized velocity and laminar flow. Closing over this finding risks early thrombosis and perioperative stroke, which is exactly why completion imaging exists.

An answer that records the finding but proceeds to close is the trap.