The most common cause of a mass in the neck that appears only on straining is a laryngocete. However, internal jugular phlebectasia may manifest in a similar manner. Dilation of the internal jugular vein with any maneuver that increases intrathoracic pressure suggests mechanical obstruction in the neck or the mediastinum, but the cause is still in doubt. Dilated internal jugular veins have been excised and have been found to have thinning of the wall of the vein, but have not been found to have a congenital abnormality.