Pulmonary Artery Intimal Sarcoma Masquerading as Pulmonary Embolism During Therapeutic Apixaban: A Case Report

Pulmonary artery intimal sarcoma (PAIS) is a rare intravascular malignancy that can closely resemble pulmonary embolism (PE). A 65-year-old man receiving therapeutic apixaban for atrial fibrillation presented with 3 weeks of progressive exertional dyspnea. Computed tomography pulmonary angiography showed a large unilateral filling defect in the left main pulmonary artery with occlusion of the left upper- and lower-lobe branches, initially interpreted as PE. However, the D-dimer was low, bilateral lower-extremity ultrasonography showed no deep venous thrombosis, cardiac biomarkers were normal, and echocardiography showed preserved right ventricular size and function without pulmonary hypertension. Contrast-enhanced chest magnetic resonance imaging demonstrated an enhancing lobulated, frond-like proximal pulmonary artery mass with mild arterial expansion and a separate distal nonenhancing component consistent with bland thrombus. Pulmonary thromboendarterectomy with tumor debulking confirmed high-grade PAIS. The patient subsequently received doxorubicin, ifosfamide, and mesna with pembrolizumab followed by proton radiotherapy. This case emphasizes that a unilateral central pulmonary artery filling defect should prompt tumor-directed imaging when the thromboembolic burden is discordant with biomarkers, venous imaging, and right-heart physiology.