Magnetic Resonance for Evaluation of the Thorax: Mediastinoscopy
Mediastinoscopy provided a sensitivity of 87.1 percent, specificity of 100 percent and an accuracy of 95.2 percent. Mediastinoscopy in this study exceeded all the other modalities as the most accurate staging method for detecting bronchogenic carcinoma.
Another study evaluating primary lung carcinoma staging comparing MR and CT found no statistically significant differences between the two imaging methods for evaluation of tumor extent or node involvement. In this study, the multiplanar capabilities of MR were useful for assessing chest wall invasion. The analysis of concordances and discordances did not indicate whether one modality could be substituted for the other, or which diagnostic strategy might be more useful. Many times MR has significantly aided the evaluation of bronchogenic carcinoma particularly for those centrally located (Fig 5) and for extension into the mediastinum, especially the aorticopulmonary window (Fig 2).
Thus, these and a variety of other reports in the literature provide divergent reports as to the utility of MR. Often, as a consequence of the differences between the various MR systems by multiple manufacturers and the MR technique used in the reported studies, the images are not comparable from one paper to the next. Perhaps this accounts for the wide spectrum of data reported on the utility of MR for evaluation of bronchogenic carcinoma. The precise role of MR for bronchogenic carcinoma and for the chest in general remains to be determined. The reader must remain aware that there are great differences between MR machines. As a result, when evaluating the literature one must analyze the techniques utilized for acquiring images of the chest and whether the images were of optimal quality for assessing the area of interest.
MR may play an important role in differentiation of radiation fibrosis from recurrent pulmonary neoplasm. As mentioned above, MR has been used to differentiate mediastinal fibrosis from recurrent tumor within the mediastinum in patients with lymphoma. A recent study has shown MR may play an important role in the differentiation of tumor from fibrosis. The long TR sequence (T2 weighted sequence) shows fibrosis as a decreased signal intensity while tumor has increased signal intensity. Usually tumors have an intermediate signal intensity on a T1 weighted sequence on MR and an increased signal intensity on a T2 weighted sequence. If the parenchymal lesion extends into the mediastinum the tumor may blend with mediastinal fat on the T2 weighted sequence.