Today we discussed a really interesting case of a middle-aged gentleman with a longstanding history of lower extremity lymphedema and several months of chylous ascites of unclear etiology, who presented with 50 lb weight loss and was found to have a small bowel obstruction.
In working through this case, it is first important to understand: what is chylous ascites?
Chylous ascites means intra-peritoneal fluid with composition resembling lymphatic fluid. There are different criteria, but definitions generally require triglyceride level >200 mg/dL (some more conservative definitions use a level of 110 mg/dL). Presence of particles such as chylomicrons can also be suggestive of chylous fluid, as can an opalescent or white/milky appearance on gross examination (though this is not specific!).
There are a few general pathophysiologic mechanisms of chylous ascites formation:
1. Increased pressure in lymphatic system: When the pressure within the lymphatic vessels increases, the result is leakage down the pressure gradient into the peritoneal cavity. This causes chylous ascites. Persistence of this physiology can lead to deposition of collagen within the lymphatic vessels, which impairs absorption and can perpetuate the problem as well as causing a protein-losing enteropathy. This cycle can be caused by multiple conditions, including lymphatic obstruction, malignancy, retroperitoneal fibrosis, increased chyle production (can be seen in cirrhosis) and circulatory congestion.
2. Inflammation in the lymphatic system: Inflammatory mediators can cause increased permeability of lymphatic vessels, allowing for leakage of lymph into the peritoneal cavity. (This mechanism is similar to why sites of superficial inflammation appear edematous and red from leaky capillaries). Conditions leading to this outcome include certain infections, notably filiariasis, which is infection with the roundworm wucheria bancrofti. This entity causes dramatic lymphatic inflammation, which can result in a condition called elephantiasis in addition to chylous ascites.
3. Structural abnormality in lymphatic system: The lymphatic system can have either congenital or acquired structural abnormalities that predispose to leakage and development of chylous ascites. Congenital causes are rare. Congenital lymphangiectasia is a condition in which lymphatic vessels commonly lack valves necessary to support lymphatic flow, which can result in dilation, stasis, and leakage throughout the lymphatic system. Acquired causes include damage to the thoracic duct through trauma or as a post-operative complication.
Differential for chylous ascites includes (but is not limited to!):
- GI tumors (particularly small bowel) including lymphoma, neuroendocrine tumor, Kaposi’s sarcoma
- MAI (usually in HIV/AIDS patients)
- wucheria bancrofti (filiariasis)
- Whipple’s disease
- post-radiation fibrosis
- constrictive pericarditis
- nephrotic syndrome
- retroperitoneal fibrosis
- post-operative or traumatic thoracic duct injury
- dilated cardiomyopathy or RH failure
- congenital lymphangiectasia
Our patient’s presentation was concerning for something luminal in the small bowel. Ultimately he was evaluated with push enteroscopy and biopsy of the jejunum, which showed lymphangiectasia, lymphedema, expansion of the lamina propria and small bowel mucosa. For this patient’s constellation of symptoms – starting with unexplained chronic lymphedema, then chylous ascites and a small bowel obstruction – congenital lymphangiectasia is a highly possible diagnosis. This condition can cause SBO by dilated lymphatics becoming large enough to block transit through the bowel, and sometimes lymph can thrombose in areas of stasis. This condition is generally managed with dietary changes (diet high in medium-chain triglycerides). Our patient is awaiting a lymphangiogram for further evaluation of the structure of his lymphatic system.