Hepatopulmonary syndrome (HPS) refers to the combination of
- hepatic dysfunction (cirrhosis)
- hypoxemia (alveolar-arterial O2 gradient of >15 mmHg; >20 mmHg in >64 years old patients)
- peripheral pulmonary arterial dilatation (due to right to left micro-shunts)
It is estimated to be present in ~15% of adults with liver cirrhosis.
Arterial hypoxemia in patients with hepatopulmonary syndrome is thought to occur because of excessive production of vasodilators, formation of subpleural arteriovenous microshunts (that resemble spider angiomas) and in some patients, macroscopic pulmonary AVM's, producing ventilation-perfusion mismatch and limitations in oxygen diffusion.
The radiologic manifestations of this disease include distal vascular dilatation associated with an abnormally large number of visible terminal vessel branches, which are always concentrated in the lower lung zones.
Chest x-ray may include bibasal medium-sized (1.5-3 mm) nodular or reticulonodular opacities 2,4
May show peripheral arteriolar dilatation on CT with an increased number of terminal branches extending towards the pleura.
Two patterns have been described on CTPA 6:
- most common (~85%)
- manifests as distal vascular dilatation with subpleural telangiectasia
- features include multiple, slightly dilated subpleural vessels that do not taper normally and therefore extend to the pleural surface
- less common (~15%)
- seen as individual arteriovenous malformations on angiograms and nodular dilatation of peripheral pulmonary vessels
Nuclear medicine - scintigraphy
Tc-99m MAA (micro-aggregated albumin) lung scan is a useful method to detect intrapulmonary vascular dilatation. A scan showing uptake of radionuclide over the kidneys, brain, or both suggests shunting through the lung caused by an intrapulmonary shunt. The perfusion lung scan is a simple, safe, noninvasive and effective method to evaluate intrapulmonary vascular dilatation associated with right-to-left shunts.
- pulmonary complications of cirrhosis and portal hypertension
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