Obstruction of the superior vena cava or subclavian veins: sonographic diagnosis.

The normal subclavian vein shows a respiratory rhythmicity on sonograms and responds to a sudden sniff maneuver by collapsing in a rapid, transient manner secondary to the sudden decrease in intrathoracic pressure. Of 11 patients studied using ultrasound (US) for possible superior vena cava (SVC) obstruction, five patients with proved SVC obstruction had no response of the enlarged subclavian veins to respiratory maneuvers. One patient with a partial obstruction had a minimal response on one side. Two patients with isolated subclavian vein obstructions had no response on the affected side and a normal response on the contralateral side. Three patients proved not to have SVC obstruction had normal responses. Sonography of the subclavian veins may be an effective, indirect screening technique for the presence of SVC obstruction and can also be used to evaluate the patency of the subclavian vein, although the sensitivity and specificity of the method remain to be determined from a larger, prospective study.