Table 164-1.
CAUSES OF PLEURAL EFFUSION AND CRITERIA FOR DIAGNOSIS
| Causes of Pleural Effusion | Distinguishing Radiographic Findings | Fluid Patterns | Other Diagnostics |
|---|---|---|---|
| Common Diseases | |||
| Pyothorax | Effusion may be unilateral or encapsulated; rounded or collapsed lung lobes (constrictive pleuritis) | Septic exudate | CBC; fluid culture |
| Feline infectious peritonitis | Concurrent abdominal effusion in some cases; rounded or collapsed lung lobes (constrictive pleuritis) | Nonseptic exudate (pyogranulomatous) | Fluid protein electrophoresis; Serology; PCR, immunostain |
| Congestive heart failure | Cardiomegaly; pulmonary edema and venous congestion; dilated caudal vena cava; abdominal effusion (rare) | Pure transudate; modified transudate; chylous effusion | Echocardiography; electrocardiography; angiocardiography |
| Heartworms (dirofilariasis) | Prominent pulmonary arteries; right-sided heart enlargement | Modified transudate; chylous effusion | Heartworm tests; echocardiography |
| Mediastinal neoplasia (lymphoma, thymoma) | Mediastinal mass (widened mediastinum; dorsally displaced trachea; caudally displaced heart and carina; esophageal compression) | Neoplastic: modified transudate; nonseptic exudate; chylous effusion | Ultrasound; fine-needle aspiration cytology |
| Bronchopulmonary neoplasia (carcinoma) | Pulmonary mass or infiltration | Neoplastic (variable): modified transudate; nonseptic exudate; chylous effusion; hemorrhage | Ultrasound; fine-needle aspiration cytology; thoracotomy |
| Chylothorax | Rounded or collapsed lung lobes (constrictive pleuritis); effusion may be unilateral | Chylous effusion | Fluid triglyceride; lymphangiogram; evaluate for underlying causes |
| Uncommon Diseases | |||
| Diaphragmatic hernia | Other signs of thoracic trauma; loss of diaphragm shadow; displaced abdominal organs; concurrent abdominal effusion | Modified transudate; nonseptic exudate | Ultrasound; contrast peritoneography |
| Hemothorax | Other signs of thoracic trauma | Hemorrhage | If nontraumatic: coagulation tests; evaluate for underlying causes |
| Lung lobe torsion | Opaque lung lobe (right middle or either cranial lobe) | Nonseptic exudate; hemorrhage | Ultrasound, bronchoscopy; thoracotomy |
| Hypoalbuminemia | Concurrent abdominal effusion | Pure transudate | Evaluate kidneys, liver, and GI tract |
| Mesothelioma | No distinguishing characteristics | Neoplastic (variable): modified transudate; nonseptic exudate | Ultrasound; fine-needle aspiration cytology; thoracotomy |
| Thymic branchial cyst | Mediastinal mass (similar appearance to mediastinal neoplasia) | Modified transudate; nonseptic exudate | Ultrasound; thoracotomy |
| Pancreatitis | Concurrent abdominal effusion | Nonseptic exudate | Abdominal ultrasound; serum pancreatic lipase immunoassay |
| Pulmonary thromboembolism | Hypovascularity of lung; blunted pulmonary arteries; right-sided heart enlargement | Modified transudate; nonseptic exudate | Angiography; pulmonary perfusion scan |