How do you differentiate and manage a fat embolism versus a pulmonary embolism (PE) detected on a computed tomography (CT) scan?

From the Guidelines

A CT PE study can differentiate between fat embolism and blood clot based on the appearance and attenuation values of the filling defects in the pulmonary vasculature. Fat embolism typically appears as multiple small, non-enhancing filling defects with fat attenuation values (-30 to -100 Hounsfield units), often distributed diffusely throughout the pulmonary vasculature, whereas pulmonary embolism (PE) presents as larger intraluminal filling defects in the pulmonary arteries 1. The management of these conditions differs significantly, with fat embolism focusing on supportive care and PE management centering on anticoagulation to prevent extension and recurrence. Key considerations in differentiating and managing these conditions include:

• Clinical context: Fat embolism often occurs after trauma, particularly long bone fractures or orthopedic procedures, while PE usually results from deep vein thrombosis.
• Imaging findings: The appearance and location of filling defects on CT scan can help differentiate between fat embolism and PE.
• Treatment approaches: Supportive care for fat embolism may include oxygen therapy, mechanical ventilation, and early fracture stabilization, while PE management involves anticoagulation with heparin or low molecular weight heparin, followed by oral anticoagulants like warfarin or direct oral anticoagulants for at least 3-6 months 1. It is essential to accurately diagnose and manage these conditions to improve patient outcomes and reduce morbidity and mortality. In cases where the diagnosis is uncertain, further evaluation with additional imaging studies or laboratory tests may be necessary to guide treatment decisions. The use of clinical decision tools and guidelines, such as those recommended by the American College of Physicians 1, can help clinicians stratify patients into groups for whom different diagnostic strategies are appropriate, ultimately leading to more effective and targeted treatment.

From the Research

Differentiation between Fat Embolism and Blood Clot

• A CT PE study can detect pulmonary embolism (PE) by showing occlusion of blood flow in a pulmonary artery, typically due to a thrombus 2.
• However, differentiating between fat embolism and blood clot using a CT scan can be challenging, as the imaging characteristics of fat embolism are not well-defined in the provided studies.
• Fat embolism is not explicitly mentioned in the provided studies, which primarily focus on pulmonary embolism (PE) and deep vein thrombosis (DVT) as manifestations of venous thromboembolism (VTE) 2, 3, 4, 5, 6.

Management of Pulmonary Embolism (PE)

• The management of PE involves assessing the clinical probability of PE, D-dimer testing, and chest imaging 2.
• Patients with a high probability of PE should undergo chest imaging, and D-dimer testing is not necessary 2.
• First-line therapy for PE consists of direct oral anticoagulants, with thrombolysis reserved for patients with systolic blood pressure lower than 90 mm Hg 2.
• Computed tomography pulmonary angiography (CTPA) is regarded as the gold standard imaging modality for investigation of acute PE, but ventilation-perfusion (VQ) scans can be used as an alternative imaging technique for diagnosing PE in those where CTPA is contraindicated 4.

Incidental Findings on CT Scans

• Incidental findings are common on CT scans performed to evaluate PE, but they are rarely clinically significant 5.
• Chest radiograph remains a reasonable initial investigation as it can aid in identifying alternative diagnoses, especially in the setting of a low pre-test probability for PE 5.