The thorax can be affected by metastatic illness in a variety of ways, the most frequent of which are lung nodules, lymph node enlargement, pleural effusion, and osseous lesions. Extrathoracic malignancies are far less likely to embolize to the lungs. Thoracic imaging tests may reveal large artery tumor emboli as pulmonary arterial filling deficiencies or “beaded”-appearing pulmonary arteries. Occasionally, tumor embolization affects only the small pulmonary arteries, causing fibro cellular intimal hyperplasia and thrombotic vascular occlusion, resulting in increased pulmonary vascular resistance and elevated pulmonary arterial pressure, potentially leading to right ventricular failure: this is known as pulmonary tumor thrombotic microangiopathy. Patients with tumor thrombotic microangiopathy may experience increased shortness of breath and growing exercise intolerance, finally developing right ventricular failure symptoms. Tissue thrombotic microangiopathy has nonspecific imaging characteristics, however thoracic computed tomography may show tiny nodular opacities with branching patterns simulating infectious bronchiolitis, or mosaic perfusion due to small artery blockage causing pulmonary perfusion derangements. Small, generally nonsegmental, mismatched perfusion deficits can be seen on ventilation-perfusion scintigraphy, and positron emission tomography can reveal hypermetabolism.
Patients with known extrathoracic malignancy who have persistent, progressive imaging abnormalities and unexplained dyspnea or hypoxemia, especially if features of pulmonary hypertension are present, maybe suspected of tumor thrombotic microangiopathy, though the diagnosis is rarely established before death.