IS Case 612: Hepatopulmonary syndrome
Imaging Sciences URMC 2011
Publication Date: 2011-12-12
The patient is a 35-year-old male, with past medical history notable for xerocytosis and liver disease (heterozygous for hemochromatosis), presenting with progressively worsening shortness of breath, clubbing, and exertional dyspnea. When walking 1000 ft. on 6L O2 supplementation the patient desaturates to 69%. Has known non-cardiac shunting from recent contrast transesophageal echo (TEE).
Nuclear medicine (NM) VQ scan reveals Tc99-MAA uptake in the kidneys and brain indicative of a systemic shunt. Given the patient’s history this is most compatible with hepatopulmonary syndrome. Large segmental matching perfusion and ventilation defects in the lingula and anterior basal segment of left lower lobe with ventilation worse than perfusion. Low probability for pulmonary embolism (PE).
The hepatopulmonary syndrome (HPS) is the triad of chronic liver disease, an increased alveolar–arterial gradient while the patient is breathing room air, and intrapulmonary vascular dilations or arteriovenous communications that result in a right-to-left intrapulmonary shunt and occurs in 4–29% of patients with cirrhosis.” 
The proposed mechanism for the hepatopulmonary syndrome is a decreased hepatic clearance of pulmonary vasodilators such as nitric oxide. The resulting vascular dilatations result in intrapulmonary shunts and increased perfusion relative to ventilation resulting in hypoxemia. The vascular involvement is typically more prominent in the lung bases. Clinically this distribution results in platypnea and orthodeoxia (Hypoxia in the seated or upright position that improve with recumbency).
Contrast echocardiography is a sensitive screening test for HPS. Intravenous microbubbles from agitated saline are injected and rather than being trapped in the pulmonary capillaries are seen to traverse the lung and appear in the left atrium after 5-10 heart beats. Similarly, macroaggregated albumin lung perfusion scanning will reveal the intrapulmonary shunts as increased systemic activity with increased radiotracer accumulating in the kidneys and brain. Perfusion imaging with Tc-MAA is a specific test for HPS and can be used to confirm the diagnosis and quantify the degree of shunting. The severity of the shunt can be assessed by placing regions of interest over the lungs, kidneys, brain, and comparing the relative counts of the lungs to the total systemic counts.
The syndrome may reverse following liver transplantation, and this form of therapy is considered to be the only true cure. Other forms of medical management are directed at decreasing the pulmonary hypertension with epoprostenol, inhibiting nitric-oxide induced vasodilation with methylene blue, and palliative TIPS in anticipation of a future transplant.
- McPhee SJ, Papadakis M. Current Medical Diagnosis and Treatment 2009. Chapter 16. McGraw Hill Lange.