Intrahepatic Portosystemic Venous Shunts: The Advantages and the Limitations of Ultrasonography

Abstract

The origin of an intrahepatic portosystemic venous shunt can be either spontaneous or acquired and is caused by liver injury or portal hypertension. The term “congenital shunt” may be more suitable than “spontaneous shunt” in the precise description of the origin of the shunt detected soon after birth, in which there is no evidence of hepatic injury. Patients with intrahepatic portosystemic venous shunts are at risk of hepatic or portosystemic encephalopathy. B-mode real-time sonography is usually the first modality to suspect the presence of an intrahepatic portosystemic venous shunt. However, the suspicion depends on the examiner's awareness of the disease and the size of the shunt. Small shunts may be undetected by B-mode real-time sonography. Doppler sonography, contrast-enhanced computed tomography, magnetic resonance imaging, and angiography can be used to confirm the diagnosis. Among these techniques, Doppler sonography is most convenient and noninvasive. The cost of a Doppler examination is also the lowest. This modality may allow calculation of the shunting blood flow. Patients with a shunt ratio exceeding 60% of the total portal blood flow are at high risk of encephalopathy. Small shunts may be missed by Doppler sonography, because small shunting blood flow may be lower than the detection range of the machine. The advantages and the limitations of sonography for the diagnosis of intrahepatic portosystemic venous shunt are discussed in this review.