Correct!
5. Unenhanced and enhanced thoracic MR
Unenhanced and enhanced imaging is integral to characterization of a number of mediastinal lesions, particularly mediastinal cysts, which are among the more common causes of mediastinal masses, particularly when incidentally detected in younger patients. In this patient, unenhanced followed by enhanced MR provides the unique ability to characterize this lesion without the use of ionizing radiation, and therefore obviates the need for repeat unenhanced and enhanced thoracic CT. 18FDG – PET scan could prove useful for evaluation of the mass, but the lesion should be further characterized with unenhanced and enhanced imaging without further exposure of this young patient to ionizing radiation. Follow up thoracic CT is occasionally useful for characterization of small, indeterminate pulmonary opacities, particularly when malignancy is considered, but would not play a reasonable role for the assessment of a nearly 6 cm mediastinal mass. Endoscopic ultrasound could prove useful for characterizing this lesion given its proximity to the esophagus (or using endobronchial ultrasound, given the proximity of the lesion to the tracheal carina), but biopsy should be avoided- if the lesion is indeed a cyst, endoscopy with biopsy could result in spillage of the cyst contents into the mediastinum and also runs the risk of introducing infection into a previously closed space.
To further characterize the lesion discovered at CT scanning, the patient was underwent thoracic MR (Figure 6).
Figure 6. Representative images from thoracic MRI. T1-weighted axial (A and B) and coronal (C) images. Axial T2-weighted imaging with fat saturation (a fluid-sensitive sequence; D and E). Axial unenhanced (F) and enhanced (G) gradient echo imaging.
Which of the following regarding this MR examination is correct? (Click on the correct answer to proceed to the seventh of nine pages)