Imaging modalities (MRI, CT, PET/CT), indications, differential diagnosis and imaging characteristics of cystic mediastinal masses: a review

Cystic mediastinal masses have traditionally represented a diagnostic dilemma with differentiation of malignant masses a particular area of concern. Each imaging modality has strengths and weaknesses in mediastinal imaging-computed tomography (CT) offers increased spatial resolution at the cost of poorer soft tissue differentiation and requiring ionizing radiation, while magnetic resonance imaging (MRI) offers superior soft tissue contrast/characterization at significantly greater cost. Ultrasound offers real-time visualization but is operator and tissue dependent. [18F]fluoro-D-glucose (F-18 FDG) positron emission tomography (F-18 FDG PET) CT provides functional information, but poorer spatial resolution. Recent advances have focused upon the use of magnetic resonance imaging to aid in characterization of cystic mediastinal lesions, particularly in the context of indeterminate CT findings. The mediastinum may be divided into three anatomic compartments: prevascular, visceral, and paravertebral. All three compartments extend superiorly from the thoracic inlet and inferiorly to the diaphragm. These compartments provide a useful framework for categorizing normal and pathologic mediastinal processes. In this article, we will review the imaging characteristics of mediastinal cystic lesions via a case-based review divided by anatomical mediastinal compartments. Characteristic imaging features and troubleshooting are particular areas of focus. Normal variants that may mimic cystic pathology are discussed. The roles of CT and MRI will be emphasized. Cases from our institution are presented as illustrative examples.