Episode 29: Hepatic Hydrothorax
A 55-year-old man with alcohol-induced liver cirrhosis was admitted to the ward complaining of progressive shortness of breath and occasional coughs. The chest x-ray and CT thorax showed a massive right pleural effusion without pulmonary parenchymal abnormalities. The abdominal ultrasound and CT abdomen revealed minimal ascites with a nodular liver. A diagnosis of hepatic hydrothorax secondary to alcohol-induced liver cirrhosis was made. Thoracocentesis was done for symptomatic relief. 1.5 Liters of pleural fluid was removed, and a sample was sent to the laboratory, along with blood for liver function tests. The laboratory findings reported that the fluid-to-serum protein ratio was less than 0.5, confirming that the fluid was a transudate. The patient then improved symptomatically.
Hepatic hydrothorax is a pleural collection associated with cirrhosis and portal hypertension without a primary cardiac, pulmonary or pleural disease.
It is an uncommon manifestation of cirrhosis, and occurs in about 4-6% of patients with clinical ascites.(1,2) The mechanism is the presence of diaphragmatic defects mainly found in the tendinous portion of the diaphragm. (1–3) Research has shown that the congenital defects in the diaphragms are actually small in a normal person, but in patients with liver disease, the increased abdominal pressure and thinning of diaphragm due to malnutrition enlarges these defects. (1) The peritoneum might herniate through these stoma forming blebs and form a pleuroperitoneal communication when it ruptures. The normal pressure in the pleural space is -7mmHg whereas the normal intraperitoneal pressure without ascites is already +6 mmHg.(4) The chest literally sucks the ascitic fluid from the peritoneal cavity.
Since the chest sucks the ascitic fluid, it would follow that the fluid in the pleural cavity should exceed the volume of ascites. This is usually, true: the ascites is typically small when compared to the quantity of pleural fluid, and some patients may develop hepatic hydrothorax without clinical ascites if the rate of fluid crossing into the pleural cavity exceeds the rate of ascitic fluid production. (1,3) Indeed, a study managed to show the occurrence of ascites after pleurodesis in patients with hepatic hydrothorax without clinical ascites.(1)
Hepatic hydrothorax is most found on the right. It may sometimes occur on the left, and, least often, bilaterally. (5,6) Why is there a right-sided predominance? The likely cause is anatomical. Congenital defects are commoner in the tendinous portion of the diaphragm, which is much larger on the right than on the left. (6) This situation is described as a “porous” diaphragm.
If pleuroperitoneal communication indeed exists, then the movement of substance across the diaphragm into the pleural space should not only be limited to the ascitic fluid in cirrhosis. This in fact is true. There are reports of peritoneal-pleural movement of dyes or radiolabeled materials through these defects. (3) A pleural collection may occur as a complication of peritoneal dialysis (7–9), chylothorax (10) and Meigs syndrome (7,13). Even air can cross the diaphragm: laparoscopic surgery sometimes complicated by a pneumothorax. (11,12) There was a study that analyzed the air in a patient with pneumothorax, and found that the air was pure carbon dioxide, which could only have come from the gas insufflated into the abdomen for laparoscopy. All of these fluid collections are predominantly right-sided. More interestingly, even cells can move through the diaphragm! There are examples of recurrent right-sided haemothorax secondary to non-fibromatous uterine leiomyomas as the endometrial tissues migrate up from the fallopian tube through the porous diaphragm, implants and erodes the lung. This explains the case of haemothorax in ectopic pregnancies as well! (7)
In closing, fluid in the abdomen can cross over to the pleural cavity, causing a collection that may lead to shortness of breath. This crossing occurs due to small defects, called the pleuroperitoneal communications, and is much commoner on the right side.
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