Which imaging findings are characteristic of intrathoracic metastasis (M1a)?

Updated: Jan 28, 2019
  • Author: Omar Lababede, MD; Chief Editor: Eugene C Lin, MD  more...
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The differentiation between benign and neoplastic pleural thickening/nodularity (a criterion for M1a) is a potential advantage of PET over conventional imaging. This is important since thoracocentesis can be falsely negative in 30-40% of patients with malignant pleural effusion. [24] Since PET/CT has high negative predictive value, it eliminates the need for repeated thoracocentesis or biopsies in patients with pleural abnormalities. Conversely, increased uptake on PET/CT in such patients indicates the need for further workup to evaluate for metastatic involvement.

Separate tumor nodule in the contralateral lung (another criterion for M1a) is generally detected first during the initial CT evaluation. PET/CT and MRI can further suggest the malignant nature of such lesions.

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