In endoleak evaluation, a vessel communicating with the residual aneurysm sac demonstrates flow patterns similar to which feature?

• A. Inflow-only from the artery
• B. To-and-fro directionality in the neck of a pseudoaneurysm
• C. No flow variation
• D. Turbulent venous flow

Answer: (B)

A vessel that communicates with the residual aneurysm sac shows bidirectional, to-and-fro flow because the sac acts as a small reservoir that intermittently fills and empties through a narrow channel. During systole, arterial pulsatile flow pushes blood into the sac, and during diastole, blood can recede back through the same channel, producing a characteristic to-and-fro pattern seen at the neck of a pseudoaneurysm. This pattern reflects the cyclical inflow and outflow through the communicating vessel, which is typical of endoleak channels feeding the sac.

If the flow were inflow-only from the artery, you’d see continuous forward flow without reversal. No flow variation would imply a non-pulsatile or insignificant flow, which isn’t characteristic of a sac communicating through a narrow neck. Turbulent venous flow would have a venous spectral pattern and velocity characteristics, not the arterial-to-sac bidirectional pattern described here.