What is the appropriate evaluation and management approach for an adult patient with no known medical history presenting with abdominal enlargement?

Approach to Abdominal Enlargement

In an adult patient presenting with abdominal enlargement, immediately perform percussion for flank dullness and test for shifting dullness, followed by diagnostic paracentesis with ascitic fluid analysis if ascites is confirmed, as this is the most rapid and cost-effective method to determine the underlying cause. 1

Initial Clinical Assessment

History Taking

• Question specifically about the timeline of abdominal enlargement: ascites typically develops over only a few weeks, whereas a slowly enlarging abdomen over months to years is most likely obesity, not ascites 1
• Obtain detailed risk factor assessment for liver disease: alcohol use, viral hepatitis exposure, metabolic syndrome, and lifetime body weight history (nonalcoholic steatohepatitis is causative in many patients without obvious cirrhosis risk factors) 1
• Screen for other etiologies: past history of cancer, heart failure, renal disease, tuberculosis, or lymphoma/leukemia (hemophagocytic syndrome can masquerade as cirrhosis with ascites) 1

Physical Examination Technique

• Percuss the flanks with the patient supine: if the tympany-dullness interface is higher than normally found on the lateral abdomen, test for shifting dullness 1
• Shifting dullness has 83% sensitivity and 56% specificity for detecting ascites, and approximately 1500 mL of fluid must be present before flank dullness is detected 1
• If no flank dullness is present, the patient has less than 10% chance of having ascites 1
• Assess for jugular venous distension: its presence suggests cardiac ascites (alcoholic cardiomyopathy) rather than cirrhotic ascites 1
• In obese patients, physical examination is unreliable: proceed directly to abdominal ultrasound to determine with certainty if fluid is present 1

Diagnostic Workup

Imaging

• Obtain abdominal ultrasound if physical examination is equivocal or the patient is obese to confirm the presence of ascites and screen for hepatocellular carcinoma, portal vein thrombosis, and hepatic vein thrombosis 1
• Ultrasound can distinguish giant cysts or pseudocysts that rarely mimic ascites 1

Diagnostic Paracentesis

• Perform abdominal paracentesis immediately once ascites is confirmed, as this is the most rapid and cost-effective method of diagnosing the cause of ascites 1
• The procedure is extremely safe: in a study of 4,729 paracenteses, serious complications (hemoperitoneum or bowel entry) occurred in only 1/1000 procedures, with no deaths or infections caused by the paracentesis itself 1
• Do not delay paracentesis for coagulopathy correction: complications occur in only 1% of patients (abdominal wall hematomas) despite 71% having abnormal prothrombin time 1
• Routine administration of fresh frozen plasma or platelets before paracentesis is not data-supported 1

Ascitic Fluid Analysis

• Calculate the serum-ascites albumin gradient (SAAG): SAAG ≥1.1 g/dL indicates portal hypertension (cirrhosis, cardiac ascites, Budd-Chiari syndrome), while SAAG <1.1 g/dL suggests other causes (peritoneal carcinomatosis, tuberculosis, pancreatitis, nephrotic syndrome) 1, 2
• Inoculate at least 10 mL of ascitic fluid into aerobic and anaerobic blood culture bottles at bedside to detect spontaneous bacterial peritonitis, which has high prevalence at hospital admission 1, 2
• Send fluid for cell count, total protein, cytology if malignancy suspected 1

Additional Laboratory Testing

• Measure brain natriuretic peptide (BNP) or pro-BNP if cardiac ascites is suspected: median pro-BNP is 6100 pg/mL in heart failure versus only 166 pg/mL in cirrhosis 1
• Obtain liver function tests, hepatitis serologies, and renal function to evaluate underlying causes 2

Differential Diagnosis to Consider

The most common causes of ascites include: 1

• Cirrhosis (most common)
• Alcoholic hepatitis
• Heart failure
• Peritoneal carcinomatosis or massive liver metastases
• "Mixed" ascites (cirrhosis plus another cause)
• Pancreatitis
• Nephrotic syndrome
• Tuberculous peritonitis
• Budd-Chiari syndrome
• Acute liver failure

Critical Pitfalls to Avoid

• Do not rely on fluid wave or puddle sign: these are cumbersome and perform less well compared to shifting dullness 1
• Do not assume obesity is the cause without proper evaluation: perform ultrasound if there is any clinical suspicion of ascites in obese patients 1
• Do not skip admission surveillance paracentesis: unexpected ascitic fluid infection is common at hospital presentation 1
• Do not withhold paracentesis due to coagulopathy concerns: the risk is minimal and does not justify delaying this essential diagnostic procedure 1