What is typically the most likely cause of a pulsatile neck mass?

A pulsatile neck mass is most commonly associated with the presence of a vascular structure that is under pressure, leading to the characteristic pulsation. Tortuous vessels, which refer to twisting or winding blood vessels, can create a pulsatile effect due to the turbulent blood flow that occurs when blood moves through these altered pathways. When a vessel becomes tortuous, particularly the carotid artery, it can be mistaken for a mass, but the pulsations in the neck are actually originating from the blood flow within the vessel rather than from a true mass.

While aneurysms can also present as pulsatile masses, they are less frequent in the neck compared to the phenomenon seen with tortuous vessels. Thyroid enlargement can present as a mass but generally does not exhibit a pulsatile nature since it is not vascular in the same way as blood vessels. Cardiomyopathy primarily affects the heart's ability to pump blood effectively and would not typically present as a pulsatile neck mass.

In summary, the unique nature of tortuous vessels in creating a pulsatile mass in the neck, due to their blood flow dynamics, makes them the most likely cause of such a clinical finding.