Thrombotic and nonthrombotic pulmonary arterial embolism: spectrum of imaging findings.

Along with clinical examination and laboratory tests, imaging plays a key role in the diagnosis of pulmonary embolism. Multi-detector row helical computed tomography (CT) is particularly helpful in the diagnosis of acute pulmonary thromboembolism (PTE) owing to its capacity to directly show emboli as intravascular filling defects. Although parenchymal abnormalities at CT are nonspecific for acute PTE, they may contribute to a correct diagnosis of chronic PTE, the characteristic helical CT features of which are similar to its angiographic features and include webs or bands, intimal irregularities, abrupt narrowing or complete obstruction of the pulmonary arteries, and "pouching defect." Nonthrombotic pulmonary embolism is an uncommon condition but is sometimes associated with specific imaging findings, including discrete nodules with cavitation (septic embolism), widespread homogeneous and heterogeneous areas of increased opacity or attenuation that typically appear 12-24 hours after trauma (fat embolism), and fine miliary nodules that subsequently coalesce into large areas of increased opacity or attenuation (talcosis). Knowledge of appropriate imaging methods and familiarity with the specific imaging features of pulmonary embolism should facilitate prompt, effective diagnosis. Copyright RSNA, 2003