CT pulmonary angiography for suspected pulmonary thromboembolism in dogs

Why pulmonary thromboembolism is hard to confirm

Pulmonary thromboembolism (PTE) is associated with many conditions that cause hypercoagulability, blood flow stasis or endothelial injury. Identifying at-risk patients is key to the diagnosis (Goggs et al., Journal of Veterinary Emergency and Critical Care, 2009). The CURATIVE consensus (deLaforcade et al., Journal of Veterinary Emergency and Critical Care, 2019) defines dogs at high risk of thrombosis as those with immune-mediated haemolytic anaemia (IMHA) or protein-losing nephropathy, or with more than one disease or risk factor.

Bedside tests do not settle the question:

• Echocardiography and blood tests. In 12 dogs with IMHA and respiratory distress (Goggs et al., Journal of Small Animal Practice, 2014), echocardiography, cardiac troponins, D-dimers and thromboelastography did not discriminate PTE, although the sample was small.
• D-dimer. In 25 dogs, 6 with PTE on CT pulmonary angiography (Marschner et al., The Veterinary Journal, 2017), thromboelastography alone could not identify dogs with PTE. A D-dimer above 0.3 mg/L had 100% sensitivity and 71.4% specificity.
• Silent PTE. In 22 dogs with inflammatory protein-losing enteropathy that had thoracic and abdominal CT angiography (Oishi et al., Journal of Veterinary Internal Medicine, 2025), 3 had thromboembolism. The dogs with a pulmonary artery or external iliac artery thrombus showed no related clinical signs.

When CT pulmonary angiography is indicated

The 2009 review suggested that CT pulmonary angiography (CTPA) may replace selective pulmonary angiography as the imaging technique of choice for PTE in small animals. The usual candidate is an at-risk dog with respiratory distress or hypoxaemia that has no clear other explanation.

General anaesthesia is not always needed. In the 12 dogs with IMHA, CTPA was performed under intravenous sedation in sternal recumbency, after stabilisation and with flow-by oxygen. It could both confirm and rule out PTE in the major pulmonary arteries of these patients.

What the evidence shows

• Clinical patients. In the IMHA study, four dogs (33%) were positive, three suspicious and five negative. All four positive dogs had discrete filling defects in main or lobar pulmonary arteries. Necropsy in three dogs agreed with CTPA: PTE in the two positive cases, none in the negative case.
• Experimental and heartworm disease. In an experimental model and heartworm-infected dogs (Jung et al., Veterinary Radiology & Ultrasound, 2010), three of eight heartworm-infected dogs developed PTE, especially in the right caudal arteries.

CT pulmonary angiography protocol at a glance

CTPA stands or falls on contrast timing and thin reconstructions. Studies in healthy dogs used bolus tracking, with enhancement of the right main pulmonary artery within seconds (Habing et al., Veterinary Radiology & Ultrasound, 2011). With a fixed injection rate, peak enhancement fell as body weight rose. Matching injection duration to scan duration (Makara et al., Veterinary Radiology & Ultrasound, 2011) removed that link with weight, which suits dogs of very different sizes. And in 64-slice CTPA (Drees et al., Veterinary Radiology & Ultrasound, 2011), thinner reconstructions showed significantly more pulmonary artery segments.

What the radiologist looks at

The radiologist sorts the study into positive, suspicious or negative, using criteria like those in the IMHA study:

Category	CTPA criteria (one is enough)
Positive	Complete pulmonary arterial occlusion; central or peripheral intraluminal filling defect(s)
Suspicious	Luminal irregularities in central or peripheral arteries; difference in luminal density between sides; multifocal alveolar pattern with no probable alternative diagnosis
Negative	None of the above

The reader also weighs:

• Secondary signs. In the experimental model, CTPA showed round hypoattenuating filling defects, dilated arteries with abrupt cut-off, pulmonary infarcts, cavitation with spontaneous pneumothorax, and migration of emboli.
• A normal variant. A focal narrowing of the right cranial pulmonary artery was present in all healthy dogs and should not be mistaken for stenosis.
• Image quality. Motion and poor enhancement cause indeterminate studies, and breath-holding is not possible under sedation.
• Thrombi elsewhere. When the abdomen is included, as in the protein-losing enteropathy study, thrombi outside the lungs can be found.

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• A suspicious scan may reflect small or subsegmental emboli. Repeat scans or thinner reconstructions might help.
• There is no canine gold standard. CTPA has not been compared with ventilation/perfusion scanning or selective angiography in dogs, and detection at lobar and sublobar level with thin-slice CTPA remained to be established in healthy-dog work.
• A negative scan needs a cause. In three dogs with negative scans, no other explanation for respiratory distress was found. The authors list reduced oxygen content, metabolic acidosis, pain, anxiety and glucocorticoids as possible causes.

What to include when you request a CTPA report

• signalment: age, breed and sex
• the underlying disease and other thrombotic risk factors
• respiratory signs, oxygen saturation or blood gas results
• echocardiography findings, D-dimer and thromboelastography if available
• current antithrombotic treatment
• whether the patient will be sedated or anaesthetised
• whether the abdomen should be included to look for other thrombi

How Veheri can help

Veheri provides veterinary teleradiology and reports thoracic CT studies remotely for clinics. For other urgent cases, see the crucial role of emergency CT, and for the lung parenchyma, thoracic CT for pulmonary metastases in dogs.