Difficulty in Distinguishing Pulmonary Arterial Intimal Sarcoma from Pulmonary Thromboembolism Using FDG PET/CT

Pulmonary arterial intimal sarcoma (PAIS) is a rare malignant soft tissue tumor that is difficult to differentiate from pulmonary thromboembolism (PTE). Therefore, pre-operative diagnosis is often difficult. However, recent advances in fluorodeoxyglucose positron emission tomography (FDG-PET) have enabled the use of standardized uptake values (SUVs) for the differential diagnosis of PAIS from PTE, and the frequency of diagnosis of PAIS has increased. Here, we report a case of PAIS that was difficult to differentiate from PTE despite using FDG-PET.

A 40-year-old woman presented with gradually worsening exertional dyspnea. Contrast-enhanced computed tomography (CT) revealed lesions with poor enhancement in the right lateral basal pulmonary artery. FDG-PET/CT did not reveal any tumor or thrombosis in other areas. Cytological evaluation using a right ventricular catheter did not lead to a definitive diagnosis. Because the patient did not respond to anticoagulation, we performed pulmonary artery endarterectomy. Pathological examination of the pulmonary artery tumor revealed a mucinous tumor with an edematous stroma and spindle-shaped tumor-cell proliferation, which confirmed the diagnosis of PAIS. However, FDG/PET demonstrated a low SUV of 3.4.

Some PAISs with low cellular densities and high mucous tissue proportions have SUVs similar to those in PTE. In patients with low FDG uptake, if PAIS is suspected based on other objective findings, additional exploration using highly invasive tests or surgical procedures specific to PAIS is warranted.