Hepatic Hydrothorax Pathophysiology and Clinical Presentation

Anatomical and Physiological Basis

Hepatic hydrothorax occurs predominantly on the right side (73-88% of cases) because small diaphragmatic defects are more frequently located on the right hemidiaphragm, allowing ascitic fluid to move directly from the peritoneal cavity into the pleural space through these defects driven by negative intrathoracic pressure during inspiration 1, 2, 3
The mechanism involves direct fluid passage from the peritoneal cavity through these microscopic or small diaphragmatic defects, with negative intrathoracic pressure during inspiration creating a pressure gradient that facilitates fluid movement 2, 3

In peritoneal dialysis-associated pleuro-peritoneal leaks, 88% occur on the right side 1

Approximately 9% of patients with hepatic hydrothorax have no clinically apparent ascites, which can make diagnosis challenging and should not exclude the diagnosis if other criteria are met 4
The serum-to-pleural fluid albumin gradient (SPAG) >1.1 g/dL remains diagnostic even in the absence of visible ascites 4

The right-sided predominance of hepatic hydrothorax is opposite to traumatic diaphragmatic hernias, where left-sided injuries are more common (50-80%) due to the protective effect of the liver on the right side during trauma 5