Which imaging modality is first-line for evaluating suspected pleural effusion in a dog or cat?

• A. Thoracic radiography
• B. Thoracic ultrasound
• C. Computed tomography
• D. Magnetic resonance imaging

Answer: (A)

Starting with thoracic radiographs is most practical when pleural effusion is suspected in a dog or cat. They’re quick, widely available, and give a broad view of the chest to detect fluid in the pleural space. On radiographs you’ll look for signs such as blunting or disappearance of the costophrenic angles, fluid layering on a lateral view, and overall lung compression from the fluid. These images also help you assess the lungs for concurrent issues like edema, pneumonia, or a mass that could be contributing to the problem.

Ultrasound is an excellent next step because it’s highly sensitive for detecting small amounts of fluid and it lets you guide thoracentesis to sample or drain safely. However, it’s typically employed after initiating evaluation with radiographs. CT or MRI provide more detail but are not first-line due to cost, availability, and the need for anesthesia in some cases.

So, radiographs are the best starting point to screen for a suspected pleural effusion and to plan the next steps in diagnosis and treatment.