Why Right-Sided Hepatic Hydrothorax is More Common
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, 4
Anatomical and Physiological Basis
The right-sided predominance is explained by several anatomical factors:
Diaphragmatic defects are more common on the right side due to the embryological development of the diaphragm and the anatomical relationship between the liver and right hemidiaphragm 2, 3, 5
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, 6
The right hemidiaphragm has thinner areas that are more susceptible to developing these defects in the setting of increased intra-abdominal pressure from ascites 7
Clinical Distribution Pattern
The actual distribution of hepatic hydrothorax demonstrates clear right-sided predominance:
- Right-sided effusions occur in 73% of cases 4
- Left-sided only effusions occur in 17% of cases 4
- Bilateral effusions occur in 10% of cases 4
- In peritoneal dialysis-associated pleuro-peritoneal leaks, 88% occur on the right side 1
Important Clinical Caveat
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 5. The serum-to-pleural fluid albumin gradient (SPAG) >1.1 g/dL remains diagnostic even in the absence of visible ascites 5, 4.
Contrast with Traumatic Diaphragmatic Injuries
It's worth noting that this right-sided predominance 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 1. This distinction helps differentiate hepatic hydrothorax from traumatic causes.