What imaging finding is critical for diagnosing a pulmonary embolism?

In the diagnosis of a pulmonary embolism, the presence of an intraluminal filling defect is a critical imaging finding. This feature represents a blood clot that has lodged in the pulmonary arteries, obstructing blood flow. On imaging studies, particularly a CT pulmonary angiogram, this filling defect appears as an area that does not enhance with contrast material, contrasting sharply against the opacified vessel walls. This clear delineation helps radiologists and clinicians confirm the presence and location of the embolus, which is essential for effective diagnosis and subsequent management of the condition.

While the abrupt cutoff of a pulmonary artery is a notable sign, it is often not as definitive on its own as the intraluminal filling defect, which provides a direct visual cue of the obstruction. Similarly, an unexplained absence of arteries might suggest various pathologies but lacks the clarity that a filling defect provides in confirming an embolism. Absent venous drainage is also less specific and can result from other causes unrelated to embolism. Thus, recognizing the intraluminal filling defect is vital for accurately diagnosing a pulmonary embolism.