A closer view of a thromboembolus filling a main pulmonary artery reveals a layered appearance, typical of a thrombus that formed in a large vein of the pelvis or lower extremity.

• 肺动脉主干内的血栓栓子近距离外观显示分层结构，这是骨盆或下肢大静脉血栓的特征表现。