Isolated pulmonary embolism - a specific clinical entity?

Pulmonary embolism in classical meaning is a complication of deep vein thrombosis (usually in the leg veins), developing after a part of the thrombus dislodged and got wedged in pulmonary arteries. However, in half of the patients with pulmonary embolism, deep vein thrombosis is not found. One potential explanation is a different, less common location of the thrombus or previous complete embolization of the whole thrombotic mass. Another possibility is pulmonary artery thrombosis in situ, which is a specific clinical entity associated with some typical risk factors. It develops in the place of vascular injury, as a consequence of hypoxia, inflammatory changes, endothelial dysfunction and injury. Pulmonary artery thrombosis in situ can be a complication after lung resection, radiation therapy, chest trauma, in the patients with Behçet´s disease, sickle cell anemia, chronic obstructive pulmonary disease, tuberculosis or covid pneumonia. Pulmonary artery thrombosis in situ may differ from classical pulmonary embolism in prognosis as well as in therapeutic approach.