Acute Pulmonary Embolism: Key CT Angiography Findings and Diagnostic Insights

Computed Tomography Pulmonary Angiography (CTPA) plays a pivotal role in the diagnosis of acute pulmonary embolism (PE), offering clinicians a non-invasive yet highly effective imaging method to visualize blood flow within the pulmonary arteries. By injecting an iodinated contrast agent intravenously, CTPA enables detailed visualization of vascular structures, making it possible to detect blockages caused by blood clots.

Understanding CT Enhancement in Pulmonary Artery Imaging

Enhanced CT scans are specifically designed to highlight areas of abnormal blood flow. In cases of pulmonary embolism, the most telling sign is a pulmonary artery filling defect—a region where contrast fails to fill the vessel due to the presence of a thrombus. This appears as a dark area within the bright, contrast-filled pulmonary artery, clearly indicating obstruction.

Limits of Detection: When Small Clots Go Unseen

While CTPA excels at identifying large central or lobar artery clots, its ability to detect smaller, peripheral emboli is limited. Subsegmental or distal branch clots may not be clearly visible due to lower spatial resolution or motion artifacts, leading to potential false-negative results. Radiologists and clinicians must remain cautious—even with a negative CTPA, the clinical suspicion for PE should not be automatically dismissed.

The Importance of Clinical Correlation

A normal CTPA does not entirely rule out pulmonary embolism, especially in patients presenting with high pre-test probability based on symptoms like sudden shortness of breath, chest pain, or hypoxia. In such cases, further evaluation using D-dimer testing, ventilation-perfusion (V/Q) scanning, or even repeat imaging may be warranted to avoid missed diagnoses.

Ultimately, while enhanced CT remains the cornerstone of PE diagnosis, it should be interpreted within the broader clinical context. Combining imaging findings with patient history, risk factors, and laboratory data ensures more accurate assessment and timely intervention, ultimately improving patient outcomes.