Malignant ascites is defined as the abnormal accumulation of fluid in the peritoneal cavity of patients with malignancies of the ovaries, breast, colon, lung, pancreas, stomach or liver. The prognosis of this disease is poor as the patients often succumb within four months after the diagnosis.
Malignant ascites accounts for only 10% of all cases of ascites . 80% cases of malignant ascites are secondary to epithelial malignancies of the breast, ovaries, endometrium, colon, stomach, and pancreas while 20% cases are due to unknown malignancies . Chylous ascites is encountered in lymphomas. Peritoneal carcinomatosis and malignant ascites are not synonymous as is often believed  and some patients can have two causes for the development of malignant ascites e.g. cirrhosis and peritoneal carcinomatosis.
As malignant ascites typically develops in advanced or recurrent cancers, the patients may be severely debilitated at presentation. Symptoms may include dyspnea, anorexia, as well as early satiety, vomiting, nausea, pain, poor exercise tolerance with weight gain, especially an increase in abdominal girth (pants do not fit). The patients may complain of bloating sensation or feeling of heaviness in the abdomen along with generalized abdominal discomfort. Increase in the intraabdominal pressure due to the ascites can lead to symptoms of esophageal reflux, delayed gastric emptying with indigestion, nausea, and vomiting.
The workup of malignant ascites starts by obtaining a detailed patient history which, in most cases, will provide information about the underlying malignancy. Physical examination may reveal bulging flank along with flank dullness (with fluid accumulation >1.5 liters). A fluid wave and shifting dullness may also be seen. Serial measurements of abdominal girth at the level of the umbilicus help to note down the fluctuations in ascites volume. Routine laboratory tests like complete blood count, liver function tests, serum proteins are obtained. As physical examination and radiology cannot differentiate between benign and malignant ascites, cytological analysis of ascites fluid has become the gold standard for the diagnosis of this condition .
A plain abdominal radiograph may show a “ground-glass” or hazy appearance. Ultrasound or computed tomography helps to detect the free fluid. The presence of ascites can be confirmed through paracentesis of 10 to 20 ml of fluid. The calculation of serum-ascites albumin gradient (SAAG) is done by subtracting the albumin concentration in the ascitic fluid from the albumin concentration in serum . SAAG <1.1 g/dl excludes portal hypertension from the differential diagnosis. Microscopic, chemical and cytological analysis of the ascitic fluid is essential to differentiate between various etiologies of this disease. Cytologic analysis has a sensitivity of 97% when detecting peritoneal carcinomatosis  , but has a low sensitivity in diagnosing other types. The ascitic fluid in peritoneal carcinomatosis has raised levels of proteins and a low SAAG . The location of the carcinoma can be detected by biochemical markers in conjunction with cytologic studies, immunohistochemical staining . Ascites can be caused by various factors and so the diagnostic value of tumor markers may be questionable . So far, no tumor markers with high sensitivity and specificity have been reported .
The primary source of the malignancy can be detected by various tests. In female patients, laparoscopy or laparotomy can be advised to obtain tissue diagnosis as malignant ascites secondary to an ovarian malignancy is responsive to chemotherapy and tumor debulking and has better survival outcomes. But in males, it is not helpful to pursue further investigations as detecting the site of the primary tumor may not influence the management or the outcome.