MR imaging in the management of thoracic malignancies.

CT remains the modality of choice for evaluating patients with a thoracic malignancy. In specific cases MR imaging can provide useful information that cannot be obtained with CT, and thus is useful as a problem solving tool. Advantages of MR imaging include superb demonstration of vessels and vessel/mass relationships, direct multiplanar imaging capability, and the potential for tissue characterization. MR imaging is useful in staging the patient with lung cancer when vascular or mediastinal invasion is in question. Its specific applications in surgical planning include the question of chest wall invasion, brachial plexus involvement, and transgression of the diaphragm, pericardium, or lung apex. Multiplanar imaging is useful in radiation therapy planning, displaying lesion extent in a coronal or sagittal format rather than on multiple axial images. Multiplanar capability also resolves problem areas for CT such as the aortopulmonic window, subcarinal region, and lesions at the cervicothoracic or thoracoabdominal junction. Structures such as the trachea and superior vena cava can be evaluated in their plane of anatomic orientation. Routine spin-echo and fast (GRASS) imaging of mediastinal vessels is useful in the evaluation of venous thrombosis as a result of catheters or tumors. The diagnosis and follow-up are obtained without the use of intravenous contrast material or radiation. When CT cannot evaluate vessels adequately because of surgical clip artifacts or postoperative distortion of anatomy, MR imaging is useful in the determination of vessel patency as well as identification of tumor recurrence. Cardiac masses are very well demonstrated by MR imaging. A unique feature of MR imaging is its potential for tissue characterization and ability to assess disease activity. Lymphoma evaluation is an active area of research. MR imaging can evaluate the radiated patient for tumor response and recurrence. Fibrous tissue remains of low signal intensity on T2-weighted images, whereas tumor has increased signal intensity. MR imaging may detect tumor recurrence before an increase in the size of a residual lymphoma mass and before clinical recurrence is evident. The area of increased signal can also serve as a guide to the appropriate site for biopsy to confirm recurrence. In addition, MR imaging can help characterize some adrenal and liver masses, potentially helping to avoid more invasive diagnostic procedures. At the current time MR spectroscopy does not have a clinical role in thoracic malignancies, but it may be a powerful tool in the future for diagnosis and management.