The anterior mediastinum: anatomy and imaging procedures

The mediastinum is divided into compartments (anterior, middle, posterior) on the basis of lateral chest radiographs. Several anatomical and radiological classifications of the mediastinum are reported in the literature. Most mediastinal abnormalities are initially suspected following chest radiography; the need for further investigation and the most appropriate imaging modality are largely dictated by the tentative diagnosis made on this examination. Although routine chest radiography initiates the evaluation of mediastinal disorders, it is rarely diagnostic: notable exceptions are teeth or bones within a mass, which are diagnostic of a teratoma; air/fluid levels suggest an oesophageal origin, hernia, cyst, or abscess. Chest radiography is followed by spiral computed tomography (sCT). However, even sCT with contrast material is occasionally diagnostic (a confident diagnosis can be made of some lesions such as mature teratoma and mediastinal goiter) but is usually sufficient for preoperative evaluation before mediastinotomy or mediastinoscopy: it is instrumental in planning further diagnostic workup. In certain cases, magnetic resonance imaging (MRI) may be complementary to sCT, but its use is not considered routine. Besides, although the anterior mediastinum is suitable for sonographic examination, the diagnostic value of ultrasonography has not been fully exploited. Thyroid scanning with radioactive iodine is useful in identifying and evaluating masses of suspected thyroid origin. The role of fluorodeoxyglucose positron emission tomography (FDG-PET) in mediastinal diseases continues to be evaluated: it has potential for differentiating between benign and malignant disease and is expected to play a more extensive role in the imaging of mediastinal neoplasms in the future. In this paper, the radiological features of masses located in the anterior mediastinum are discussed, with particular reference to radiographic and CT patterns useful to the clinician's everyday practice.