Hepatopulmonary syndrome other imaging findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2]

Overview

Angiography may be helpful in the diagnosis of hepatopulmonary syndrome. Non-invasive studies are preferred in diagnosis and management of patients with hepatopulmonary syndrome. Pulmonary angiography is indicated in known cases of HPS if sever hypoxia (partial pressure of oxygen is < 60 mmHg) is present, if the patient is a poor responsive to 100% oxygen, and if there is a strong suspicion of direct arterio-venous communications that would be amenable to embolization, based on chest CT scan findings. Rather than direct visualization of the pulmonary dilations (IPVSs), it can also demonstrate type of micro dilation in pulmonary vasculture.

Technetium 99m-labeled macroaggregated albumin scanning also may be helpful in the diagnosis of hepatopulmonary syndrome. labeled albumin macroaggregates (>20 microns in diameter) are injecting intravenously. Macroaggregates exceed the normal pulmonary capillary diameter and should be trapped normally. Scans that identify uptake of the radionucleotide by the brain suggest that the macroaggregates passed through either an intrapulmonary or intracardiac shunt. A calculated shunt fraction of above 6% is abnormal. Nevertheless, it can not distinguish between intracardiac and intrapulmonary shunting and has a lower sensitivity compared to contrast-enhanced echocardiography.

Other Imaging Findings

Pulmonary angiography

Non-invasive studies are preferred in diagnosis and management of patients with hepatopulmonary syndrome. Nevertheless in some cases such as likelihood of tromobotic accident, or when other noninvasive studies were not diagnostic, it is needed to evaluate the patient by means of angiography.

Indication for pulmonary angiography in known cases of HPS are as follows:

• Sever hypoxia (partial pressure of oxygen is < 60 mmHg),
• Poor response to 100% oxygen
• Strong suspicion of direct arterio-venous communications that would be amenable to embolization, based on chest CT scan findings.

Rather than direct visualization of the pulmonary dilations (IPVSs), it can also demonstrate type of micro dilation in pulmonary vasculture as follows:

• Type 1 (minimal):Finely diffuse, spidery infiltrates; may progress to type 1 (advanced).
• Type 1 (advanced): Diffuse spongy or blotchy angiographic appearance
• Type 2: Discrete, localized arterio-venous communications

Technetium 99m-labeled macroaggregated albumin scanning

• labeled albumin macroaggregates (>20 microns in diameter) are injecting intravenously.
• Macroaggregates exceed the normal pulmonary capillary diameter and should be trapped normally.
• In normal physiologic status, particles greater than 20 microns in diameter, (normal range of pulmonary capillary diameter is less than 8 to 15 microns) are trapped and filtered by the pulmonary capillary bed and do not appear in the left side of the heart and general circulation. However, in the presence of an intrapulmonary or intracardiac right-to-left shunt, those particles may be detected either in the left heart chambers or in the other organs such as brain or kidneys.
• Scans that identify uptake of the radionucleotide by the brain suggest that the macroaggregates passed through either an intrapulmonary or intracardiac shunt.
• Shunt fraction is defined as the percent of uptake in the brain compared to lungs.
• 3% to 6% of albumin macroaggregates pass through the pulmonary vasculature in normal patients;Hence, a calculated shunt fraction of above<math>></math> 6% is abnormal.
• The radionucleotide is also taken up by other organs, and the shunt fraction can be calculated in the kidneys as well.
• Nevertheless the brain is preferred to the other organs and particularly kidneys because:
• Free technetium deposits in the kidney but not in the brain and hence could falsely elevate the calculation.
• Renal blood flow decreases significantly in cirrhotics and anemic patients with hyperdynamic circulation, on the other hand, the cerebrum perfusion maintains fairly constant in patients with anemia and most of cirrhotics (needs further investigation).
• limitations
• Can not distinguish between intracardiac and intrapulmonary shunting
• lower sensitivity compared to contrast-enhanced echocardiography

• 

  A schematic view of Technetium 99m-labeled macroaggregated albumin scanning . Particles bigger than 20 microns should not pass through the pulmonary vasculature and should be trapped in healthy subjects (1, 2, 3 ), but in patients with shunts such as patients with hepatopulmonary syndrome, they will appear in the left heart and the systemic circulation subsequently (4, 5, 6). Artwork by Soroush Seifirad, MD.