What is the role of imaging in determining mediastinal invasion of the primary tumor for lung cancer staging?

Updated: Jan 28, 2019
  • Author: Omar Lababede, MD; Chief Editor: Eugene C Lin, MD  more...
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Mediastinal invasion by the primary tumor can be reliably depicted using CT scanning or MRI. This is one of the important criterion in staging lung cancer, since it can determine resectability of the tumor.

In some cases, mediastinal invasion can be grossly visible (eg, significant replacement of the fat by the soft tissue of the tumor or encasement of a vascular structure or other structures by the neoplasm). Otherwise, the contiguity of the tumor with the mediastinum does not necessarily imply invasion. It was suggested that although CT cannot confirm mediastinal invasion in such cases with certainty, it can separate masses that were likely to be technically resectable (no invasion or focal limited invasion). [23] This separation of the resectable lesions is based on the presence one or more following CT findings:

  • Contact between mass and mediastinum of less than 3 cm

  • Circumferential contact between the mass and aorta of less than 90°

  • Presence of a fat plane between the mass and the mediastinal structures

Using the reverse criteria is less reliable in predicting irresectability. For example, a fat plane between the mediastinum and mass can be obliterated not only by invasion, but also by technical factors (eg, motion artifacts and volume averaging). The presence of more than 3 cm of contact or more than 90° of encasement has low sensitivity in confirming invasion.

MRI can be used in cases with questionable CT findings, given its superior tissue contrast and multiplanar capabilities. In a study from 2013, the sensitivity in nonspecific CT, CT with contrast-enhancement, and MR angiogram for detecting mediastinal and hilar invasion where 78-90%, 73-87%, and 75-88%, respectively. [16] MRI can delineate infiltration or disruption of the extrapleural fat planes, which suggests chest wall invasion. This can be further enhanced by the administration of intravenous contrast and other nonemergent techniques such as dynamic cine MRI.

The combined PET/CT is more accurate than PET alone in detecting chest wall and mediastinal invasion. However, there is limited added value of PET/CT over CT in T assessment. [24]

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