Non-thrombotic pulmonary emboli: imaging findings and differential diagnoses

Nonthrombotic pulmonary embolism (NTPE) encompasses a diverse group of rare but clinically significant conditions that involve fat, tumor, air, amniotic fluid, septic, parasitic, and iatrogenic emboli. This review summarizes the pathophysiology, imaging findings, and differential diagnoses of NTPE toward the goal of facilitating its accurate radiologic diagnosis.

In NTPE, the use of computed tomography pulmonary angiography (CTPA) may reveal filling defects in the pulmonary arteries; however, the embolus is often not directly visualized, especially in cases of microscopic emboli. NTPE-related pulmonary lesions arise from two mechanisms: mechanical obstruction and chemical injury. Clarifying the link between these mechanisms and imaging features is crucial for achieving the accurate diagnosis of NTPEs. Tools such as dual-energy CT and ventilation-perfusion scintigraphy contribute to the detection of microvascular involvement. We present the characteristic imaging patterns and diagnostic pitfalls for each NTPE subtype, illustrated with representative cases.

The awareness of NTPE entities and their imaging features is essential for the timely diagnosis and management of these emboli. Radiologists should consider the possible presence of an NTPE in patients with unexplained respiratory symptoms, especially when conventional imaging fails to demonstrate thrombotic emboli.