Chylous ascites

Last revised by Daniel J Bell on 8 Dec 2021

Chylous ascites (also known as chyloperitoneum) is defined as the abnormal intraperitoneal accumulation of milky lymphatic fluid with a triglyceride level >110 mg/dL 1. Etiologically it is due to a disruption of the lymphatic system, most commonly obstructive due to a mass or traumatic (which maybe iatrogenic).

  • abdominal distension
  • abdominal discomfort
  • dyspnea: splinting of the diaphragm by ascites
  • sequelae of hypoproteinemia: edema
  • acute abdomen: acute chylous peritonitis 2

For fluid aspirated from the abdomen to be chyle, triglycerides need to be elevated above 110 mg/dL (two to eightfold more than normal plasma concentration) with a specific gravity >1.012. 

The pathogenesis of chylous ascites relies upon a disruption to the normal lymphatic pathways 1,2:

  • obstruction of the lymphatics: usually a mass e.g. malignancy
  • fistula between the lymphatics and the peritoneum/mesentery: usually trauma or surgery
  • leakage of retroperitoneal megalymphatics: usually congenital

Large volume fluid in the peritoneal cavity is the normal finding. However, if the patient is allowed to remain supine for a short interval then the fat commonly rises to the top of the fluid (fat is less dense than water), producing a fat-fluid level (cf. chyluria), which is highly specific for chyloperitoneum.

On CT, chylous ascites is indistinguishable from water on density measurements. Fat-fluid levels are common.

On MRI, due to its high fat content, chylous ascites often demonstrates distinctive signal drop out on fat saturated sequences.

Morton described a case of a boy dying from chylous ascites caused by tuberculosis in 1694, the first known appearance of this condition in the literature 2.

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