Thoracic Ultrasound

Thoracic ultrasound is recommended whenever the physical examination, clinical history, or chest radiographs (X-rays) raise concern for disease inside the chest cavity:

• Labored, rapid, or shallow breathing — especially when a pet breathes with the elbows out or the neck extended, signs of respiratory distress
• Suspected pleural effusion (fluid accumulation in the space between the lungs and chest wall), which muffles the lungs and requires drainage to relieve pressure
• Suspected pericardial effusion (fluid around the heart), a life-threatening condition that impairs cardiac output
• Detection and evaluation of mediastinal masses (tumors in the central chest cavity between the lungs), common with lymphoma in cats
• Staging known cancer — determining whether a primary tumor elsewhere has spread to the chest
• Trauma: screening for pneumothorax (air in the chest cavity) or hemorrhage using rapid point-of-care TFAST (thoracic focused assessment with sonography for trauma)
• Guiding thoracocentesis (needle drainage of pleural fluid) or fine-needle sampling of chest masses, making these procedures safer and more precise

Thoracic ultrasound provides targeted but highly actionable information about chest disease:

• Pleural effusion: fluid in the pleural space (between the lung surface and the chest wall) appears as an anechoic (dark) zone on ultrasound; the volume can be estimated and the fluid localized for safe drainage. Common causes include heart failure, pyothorax (chest infection), chylothorax, and cancer
• Pericardial effusion: fluid surrounding the heart within the pericardial sac, visible as a dark halo around the cardiac silhouette; even a small volume can cause life-threatening cardiac tamponade (compression of the heart)
• Chest and mediastinal masses: soft-tissue masses against or between the lungs are well visualized; ultrasound can differentiate solid masses from fluid-filled cysts and guide biopsy needles
• Lung surface changes: the TFAST protocol evaluates the lung surface for B-lines (comet-tail artifacts indicating pulmonary edema or inflammation) and the "glide sign" (indicating whether the lung surface is moving normally — absent in pneumothorax)
• Guidance for interventional procedures: real-time ultrasound guidance for thoracocentesis dramatically improves safety by confirming the needle is entering fluid rather than lung parenchyma

Thoracic ultrasound is performed with the pet in a comfortable standing or sternal (chest-down) position — whichever position is least stressful for a pet already working to breathe:

• A small area of fur on one or both sides of the chest is clipped to allow direct skin-to-probe contact; in short-haired animals, the fur may simply be wet-parted
• Ultrasound gel is applied to the skin to eliminate the air gap between the probe and the chest wall
• The transducer (probe) is placed in the intercostal spaces (between the ribs) at multiple standardized acoustic windows and moved to survey the pleural space, lung surface, and mediastinum
• Fluid appears immediately as a dark, echo-free zone; masses appear as gray solid structures distinct from the surrounding tissues
• If thoracocentesis is indicated, the probe is used to confirm the optimal entry site and depth before the needle is placed — fluid is drained and can be sent to the laboratory for analysis

A focused thoracic scan for a specific question (e.g., confirming pleural effusion before drainage) takes only a few minutes. A comprehensive survey of the chest, including both sides and multiple windows, typically requires 15–25 minutes.

Very little preparation is needed for thoracic ultrasound, which is one of the reasons it is so useful in urgent situations:

• Fasting is not required — the chest cavity is not affected by stomach contents, unlike abdominal ultrasound
• Fur clipping: a small area on the lateral chest wall is clipped; the amount varies with coat thickness. For very thick-coated breeds, slightly larger patches may be needed for adequate image quality; the fur regrows within a few weeks
• Sedation: most dogs and cats, even those in mild respiratory distress, tolerate thoracic ultrasound with minimal or no restraint. Because the procedure is brief and non-invasive, sedation is rarely required — and is avoided in patients with compromised breathing until the immediate cause is identified and treated
• Positioning: your pet does not need to lie flat; a standing or chest-down position works well, which is important for a dyspneic (breathing-difficulty) patient who cannot tolerate being placed on its back

Thoracic ultrasound is one of the most comfortable diagnostic procedures a pet can undergo. The probe is pressed gently against the chest wall between the ribs — there is no pain involved, and the gel is simply cool to the touch. Most pets stand calmly or rest in a sternal position throughout. If your pet is in respiratory distress, the team will prioritize minimizing stress: the scan is performed in whatever position is most comfortable, with the shortest handling time needed to answer the clinical question. When pleural effusion is confirmed, thoracocentesis — draining the fluid with a needle — can often be performed during the same visit, providing immediate relief. Results are discussed with you the same day. Drained fluid may be sent to our in-house laboratory or an external pathologist for cell analysis to help determine the underlying cause.

Thoracic ultrasound uses sound waves — there is no ionizing radiation, making it entirely safe to perform repeatedly and in patients for whom radiation exposure is a concern. It is safe for young animals, pregnant animals, and patients requiring frequent monitoring. There is no known adverse effect from diagnostic ultrasound in any age group or health status. When thoracocentesis is performed under ultrasound guidance, the risk of accidental lung puncture is greatly reduced compared to blind needle placement. Our on-site imaging capability means a pet arriving in respiratory distress can be assessed and treated within minutes without transport to a referral facility for this portion of the workup. For pets whose breathing difficulty turns out to involve the heart's internal structure — valve disease or cardiomyopathy — a dedicated echocardiogram with Dr. D'Urso, our board-certified cardiologist, is the appropriate next study to fully characterize the cardiac component.