Diagnosis And Workup Of Malignant Ascites

The finding of ascitic fluid in patients with known abdominal malignancy is usually secondary to the tumor itself. Many times, however, patients present with increasing abdominal girth without other sequelae or prior diagnosis of malignancy. Non-neoplastic causes of ascites include congestive heart failure, cirrhosis, renal disease or pancreatic disease, hypoproteinemia, infectious processes such as spontaneous bacterial peritonitis or tuberculosis (Fig. 3.2). In addition, benign gynecologic conditions such as endometriosis may be associated with ascitic collection. A small amount of ascitic fluid noted on imaging studies in the pelvis or lateral gutters of an asymptomatic patient with known intraperitoneal malignancy does not need to be aspirated because in most instances it can be assumed that the fluid collection is secondary to the malignancy itself. Paracentesis is indicated when a definitive diagnosis of malignant ascites is necessary for staging purposes or when planning surgical resection of malignant disease. In these situations, laparoscopic evaluation with inspection of visceral and parietal peritoneum is extremely helpful to rule out small tumor implants.

When abdominal paracentesis is performed, routine studies include a chemistry profile of the fluid, cell count and differential, gram stain as well as stains for tuberculous organisms and routine culture of bacteria, fungi and mycobacteria. In addition, ascitic fluid should be sent for cytologic evaluation. Generally, 500 cc of abdominal fluid are sufficient to collect enough cells for cytologic evaluation. These studies should be routinely requested when fluid is removed during laparo-scopic evaluation. The character of the ascitic fluid may be indicative of the underlying diagnosis since malignant collections are most likely bloody or serosan-guineous whereas collections from underlying liver or renal disease or as a result of cardiac disease may be serous in nature. Pancreatic ascites may also give serous fluid collections.4 The specific underlying malignancy may also have characteristic ascitic fluid. An example of this would be peritoneal mesothelioma which has

a very thick whitish ascitic fluid high in hyaluronidase levels.5 Frequently, in the evaluation of patients with extensive intraperitoneal malignancy, small quantities of fluid may be secondary to lymphatic obstruction and may represent chylous fluid collections which have resulted from obstruction of retroperitoneal lymphatic channels (Fig. 3.3) or from the lower portion of the thoracic duct. In addition, patients may develop chylous ascites who have previously undergone external beam abdominal radiation since the lymphatics may be obstructed secondary to this treatment.6

When evaluating ascitic fluid either by laparoscopy or paracentesis, adequate quantities of abdominal fluid must be obtained in order to allow appropriate diagnostic testing (Table 3.2). It is to be remembered that only a minority of all causes of ascitic fluid collections are malignant. This is especially true in the pedi-atric age group where approximately one-third of patients with known malignancy will have non-malignant causes of ascites.7 Malignant abdominal effusion is most likely present when an elevated ascitic/serum ratio of protein (more than 0.4) or lactic dehydrogenase (more than 1.0) is seen. Increased elevations of

Fig 3.3. Computerized tomographic scan showing large retro-peritoneal lymphoma which was associated with chylous ascites.

Fig 3.3. Computerized tomographic scan showing large retro-peritoneal lymphoma which was associated with chylous ascites.

Table 3.2. Testing to evaluate malignant ascites

Ascites/serum ratio for protein

Cell count

Cultures

Lactate dehydrogenase Carcinoembryonic antigen CA.—125

Detection of cytokines and cytokine receptors Endoscopic ultrasound guided biopsy Laparoscopic directed aspirate and biopsy carcinoembryonic antigen (CEA) or CA-125 favor neoplasia.8 Cell counts of the ascitic fluid may be important, especially when it is noted that 10,000 erythrocytes per microliter and more than 1,000 leukocytes per microliter are characteristic of malignant effusion. In this instance, it is necessary to rule out spontaneous bacterial peritonitis by doing appropriate cultures.

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