Chylous Ascites 

Chylous ascites is the extravasation of milky chyle into the peritoneal cavity. This can occur de novo as a result of trauma or obstruction of the lymphatic system. Moreover, an existing clear ascitic fluid can turn chylous as a secondary event.

True chylous ascites is defined as the presence of ascitic fluid with high fat (triglyceride) content, usually higher than 110 mg/dL.

Chylous ascites is an uncommon clinical condition that occurs as a result of disruption of the abdominal lymphatics. Multiple causes have been described, including the following:

• Abdominal surgery
• Blunt abdominal trauma
• Malignant neoplasms - Hepatoma, small bowel lymphoma, small bowel angiosarcoma, and retroperitoneal lymphoma
• Spontaneous bacterial peritonitis
• Cirrhosis - Up to 0.5% of patients with ascites from cirrhosis may have chylous ascites.
• Pelvic irradiation
• Peritoneal dialysis
• Abdominal tuberculosis
• Carcinoid syndrome
• Congenital defects of lacteal formation

Milky ascites is subdivided into 3 groups as follows:

• True chylous ascites - Fluid with high triglyceride content
• Chyliform ascites - Fluid with a lecithin-globulin complex due to fatty degeneration of cells
• Pseudochylous ascites - Fluid that is milky in appearance due to the presence of pus

This classification is not clinically useful and has been discarded by some.

Frequency

The rarity of chylous ascites in clinical practice can be judged by the fact that only 28 cases were identified at Massachusetts General Hospital over a period of 20 years. Of these 28 patients, 4 were children. The mean age at detection in adults was 54.3 years.^[1]

A report from the 1950s estimated the incidence of chylous ascites to be 1 case per every 187,000 hospital admissions.^[2] By the 1980s, the incidence of chylous ascites has increased to 1 case in 11,584 hospital admissions, perhaps due to more aggressive retroperitoneal and cardiothoracic surgical techniques and longer survival of cancer patients.^[3]

Age and sex distribution

No differences in sex distribution have been cited, but, of the 28 patients with chylous ascites from Massachusetts General Hospital, 75% were women. Chylous ascites can occur in adult and pediatric populations. In adults, it commonly is observed in individuals aged 50-65 years.

Clinical disease associations

In adults, chylous ascites is associated most frequently with malignant conditions. These conditions particularly include lymphomas and disseminated carcinomas from primaries in the pancreas, breast, colon, prostate, ovary, testes, and kidney. Infectious diseases, such as tuberculosis^[4] and filariasis,^[5] can cause chylous ascites. In children, the most common causes are congenital abnormalities, such as lymphangiectasia, mesenteric cyst, and idiopathic "leaky lymphatics." Other congenital causes include the primary lymphatic hypoplasia associated with Turner syndrome and yellow nail syndrome and the lymphatic malformations associated with Klippel-Trenaunay syndrome.^[5] Neoplasia is an uncommon cause of pediatric chylous ascites. Recently, chylous ascites has been reported in adults in association with hepatoma, small bowel angiosarcoma, retroperitoneal lymphoma, and jejunal carcinoid.^{[6, 7]}

The incidence of spontaneous chylous ascites in patients with chronic liver diseases is estimated to be 0.5%. Fluid in the space of Disse may enter lymphatic channels in the portal and central venous areas of the liver. An increase in portal pressure can lead to increased flow of fluid into both the space of Disse and the liver's lymphatic system. Indeed, patients with cirrhosis have increased thoracic duct lymph flow.^[8] Lymphatics may spontaneously rupture in patients with cirrhosis as a result of higher than typical flow. Chylous ascites may result. Chylous ascites has been reported in patients with polycythemia vera and resulting hepatic vein thrombosis.

Abdominal surgery is a common cause of chylous ascites. The surgical procedures most frequently associated with chylous ascites are resection of abdominal aortic aneurysm and retroperitoneal lymph node dissection. In one series of 329 patients with testicular cancer who underwent postchemotherapy retroperitoneal lymph node dissection, 7% of patients developed chylous ascites.^[9] Chylous ascites is also described after peritoneal dialysis catheter insertion^[10] , after pancreatic resection^[11] , after splenorenal shunt surgery^[12] , after living donor liver transplantation,^{[13, 14]} and after laparoscopic donor nephrectomy.^{[15, 16, 17]} The review by Aalami et al provides an excellent overview of the causes of chylous ascites, as well as a history of chylous ascites management.^[5]

Pathology

Within the enterocytes of the small intestine, dietary long-chain fatty acids are re-esterified into triglycerides. Long-chain triglycerides are subsequently coated with lipoprotein, cholesterol, and phospholipid to form chylomicrons. Chylomicrons subsequently enter the lymphatic system of the small intestines. The chylomicrons gradually pass along larger omental lymphatics to the cisterna chyli located anterior to the second lumbar vertebra. The cisterna is joined by the descending thoracic, right and left lumbar, and liver lymphatic trunks, and, collectively, these form the thoracic duct, which passes through the aortic hiatus and courses through the right posterior mediastinum and eventually enters the venous system. The thoracic duct carries lymphatic drainage from the entire body, except for the right side of the head and neck, right arm, and right side of thorax. Chylous effusions may develop when these channels are injured or obstructed.^[18]

Based on animal experiments, Blalock concluded that obstruction of the thoracic duct alone was not sufficient to cause chylous ascites.^[19] Patients with a limited reserve of lymphaticovenous anastomotic channels were suspected to have greater risk of developing persistent ascites when obstruction or injury of the lymphatic channels occurred.

Clinical features

Abdominal distension is the most common symptom in patients with chylous ascites. Other clinical features include abdominal pain, anorexia, weight loss, edema, weakness, nausea, dyspnea, weight gain, lymphadenopathy, early satiety, fever, and night sweats. Fever, night sweats, and lymphadenopathy usually are observed in patients with lymphoma. Often, features of the primary illness, such as cirrhosis or of an associated malignancy, dominate the clinical picture. Rarely, it can present as acute peritonitis.^{[20, 21]}

Complications

Sepsis is the most common complication, and sudden death has been reported in patients with chylous ascites. The prognosis in adult patients with chylous ascites is poor due to its association with malignancy and severe liver disease. However, pediatric patients and adult patients with postsurgical and posttraumatic chylous ascites have a favorable prognosis.

Laboratory Studies

Routine laboratory tests may show hypoalbuminemia, lymphocytopenia, anemia, hyperuricemia, elevated alkaline phosphatase and liver enzymes, and hyponatremia. Usually, serum cholesterol and triglyceride levels are normal.

Abnormal liver enzymes are more common in patients with disseminated carcinoma than in patients with lymphoma or nonmalignant disorders. Anemia is common in patients with neoplasia.

The diagnosis of chylous ascites is made by peritoneocentesis and analysis of the ascitic fluid.

Ascitic fluid study

Color usually is white or milky. Gross milkiness of the ascitic fluid corresponds poorly with absolute triglyceride levels because turbidity also reflects the size of the chylomicrons.

The ascites triglyceride level is elevated in all patients. Typically, chylous ascites is diagnosed when the ascites triglyceride level is greater than 110 mg/dL. Levels as high as 8100 mg/dL have been described.^[3] Other authors have identified an elevated ascites:plasma triglyceride ratio (between 2:1 and 8:1) as being indicative of chylous ascites.^[5]

Other ascites tests include the following:^[1]

• Specific gravity is 1.010-1.054.
• Total fat content is 4-40 g/L.
• Glucose and amylase levels usually are normal.
• Cholesterol level usually is low.
• Leukocyte count generally is high, from 232-2560 cells/mm³, usually with a marked lymphocytic predominance.
• Total protein content varies from 1.4-6.4 g/dL, with a mean of 3.7 g/dL. This variation reflects changes in serum proteins and dietary habits.
• Microbiologic cultures usually are negative

Other diagnostic tests

• CT scan
• Lymph node biopsy
• Laparascopy
• Laparotomy
• Lymphangiography
• Bone marrow examination
• Intravenous pyelography

CT scan, lymph node biopsy, and laparotomy carry the highest yield of diagnostic information. The role of MRI is not well defined. Lymphangiography can transiently worsen chylous ascites due to the oily contrast medium used for the test.

Because chylous ascites is a manifestation rather than a disease by itself, the prognosis depends on the treatment of the underlying disease or cause.

Supportive measures can relieve the symptoms. These measures include repeated paracentesis, diuretic therapy, salt and water restriction, elevation of legs with use of supportive stockings, and dietary measures.

Lymphatic flow increases after the ingestion of a fatty meal. The fatty acids derived from short-chain and medium-chain triglycerides diffuse directly across enterocytes into the portal venous system. Their absorption does not affect lymphatic flow. However, the fatty acids derived from long-chain triglycerides are re-esterified into triglycerides in the enterocyte. They are then incorporated into chylomicrons which subsequently enter the lymphatic system.

A low-fat diet with medium-chain triglyceride supplementation can reduce the flow of chyle into the lymphatics.^[22] Typically, medium-chain triglyceride oil is administered orally at a dose of 15 mL 3 times per day at meals. However, this approach is frequently not successful. One recent case report described the successful use of orlistat (Xenical) in a patient who had difficulty complying with a low-fat diet.^[23]

If chylous ascites persists despite dietary management, the next step may involve bowel rest and the institution of total parenteral nutrition.^[13] Bowel rest and total parenteral nutrition are postulated to be beneficial in patients with posttraumatic or postsurgical chylous ascites.

Paracentesis can result in immediate symptom relief; however, reaccumulation of fluid usually follows, and patients may require repeated paracentesis. Some authorities have advocated large-volume paracentesis. Morbidity from a single tap is usually low, but complications, such as peritonitis and hemorrhage, can occur. Transfusion of albumin and/or RBCs during paracentesis may help prevent hypovolemia in patients with hypoalbuminemia or anemia.

Multiple case reports describe the use of octreotide, a somatostatin analog, in the management of chylous ascites, typically at a dose of 100 mcg administered subcutaneously 3 times per day.^{[13, 14, 24, 25, 26]} Experimental work in humans has shown that somatostatin can significantly decrease postprandial increases in triglyceride levels. This effect cannot be explained by either inhibition of gastric emptying or inhibition of exocrine pancreatic secretion.^{[27, 28]} Octreotide is most likely effective in chylous ascites on account of its ability to inhibit lymphatic flow. Indeed, in a canine model, infusion of somatostatin resulted in a decrease in lymph flow, measured via a cannula inserted into the thoracic duct.^[29]

Postsurgical chylous ascites usually resolves with supportive therapy. Early reoperation is indicated when the site of leakage is apparent and if the patient is a good operative candidate.^[30] Case reports now describe the laparoscopic treatment of chylous leaks, using suture ligation and fibrin glue to control the leak.^[31] In another report, fibrin glue applied to absorbable mesh was useful in patients with large areas of diffuse lymphatic leakage.^[32]

Peritoneovenous shunting has been used successfully in small numbers of patients with chylous ascites.^[33] However, shunt failure is common and the procedure may be fraught with complications.

Use of TIPS to successfully treat chylous ascites related to cirrhosis has been reported.^[34]

Spontaneous healing of a chylous leak has been noted after lymphangiography performed to identify a lymph leak prior to a planned surgical therapy.^[35]

Malignant chylous ascites requires specific therapy directed at the primary cause and also supportive therapy. These therapies may include chemotherapy, radiation, and surgery. Laparotomy and ligation of the leaking lymphatics, resection of a leaking small bowel segment, and removal of an obstructing tumor all have been attempted with varying degrees of success. Transient success also has been achieved with peritoneovenous shunts.

Laparotomy should not be used in pediatric patients with chylous ascites unless the condition is unresponsive to conservative therapy and a lesion that can be corrected by surgery is apparent.