Normal spectral waveforms obtained in hepatic veins. (a) Spectrum from the middle hepatic vein in a 17-year-old girl shows normal a, S, v, and D waves from right atrial pressure changes. (b) Spectrum from the middle hepatic vein in a 1-month-old girl shows a normal monophasic flow pattern.

Most people have three hepatic veins: left, middle, and right. However, accessory hepatic veins are commonly observed. The hepatic veins join the inferior vena cava immediately inferior to the diaphragm and are in open communication with the right side of the heart (19). Flow in the hepatic veins is predominantly hepatofugal (away from the liver, toward the inferior vena cava) (20). The Doppler spectral waveforms from normal hepatic veins are multiphasic, similar to those obtained in the inferior vena cava and other large systemic veins (21). The waveform in the normal hepatic vein consists of two large antegrade waves (toward the heart) that represent atrial diastole and ventricular systole; a small retrograde wave (away from the heart) that represents flow during atrial systole; and a small wave between the two antegrade waves, which is produced by overfilling of the right atrium (19,21) (Fig 16a).

The monophasic flow pattern sometimes seen in neonates (Fig 16b) is normal and may be secondary to atypical hepatic compliance due to a large horizontally positioned liver or to hepatic hematopoietic activity (22). Variations in flow pattern among the veins have been reported. Flow in the middle hepatic vein has the most consistent triphasic pattern, probably because this vein is positioned at a favorable angle for Doppler US (22). There is no variation in triphasic activity after a meal (22).

http://radiographics.rsna.org/content/28/3/691.full