Chest ImagingMediastinal mass
mass in the
mediastinum that is usually detected on posteroanterior or lateral chest radiographs. However, it may be nondepictable on chest radiography and only demonstrated on
CT scans. Once a
mediastinal mass is radiologically detected, the abnormality has to be localized within a specific anatomical division of the
mediastinum in order to generate a limited differential diagnosis. Classically the
mediastinum is divided into three compartments: anterior, middle and posterior. The anterior compartment is limited anteriorly by the sternum, and posteriorly by the anterior margin of the
pericardium,
aorta and brachiocephalic veins. The posterior compartment is bounded anteriorly by the posterior margins of the
pericardium and great vessels and posteriorly by the
thoracic vertebral bodies. The middle compartment is defined by the margins of the anterior and posterior compartments. The differential diagnosis of
mediastinal masses is listed in Table 1.
Mediastinal mass, Table 1. Causes of mediastinal masses classified according to the divisions of the mediastinum.
| Anterior mediastinum | |
| Germ cell neoplasm mediastinal |
| Lymphoma |
| Thymoma and thymic cyst |
| Thyroid mass mediastinal |
| Middle mediastinum | |
| Bronchogenic cyst |
| Lymphadenopathy mediastinal |
| Pericardial cyst |
| Thyroid mass mediastinal |
| Tracheal tumours |
| Vascular abnormalities including aortic aneurysm, aortic dissection, vascular variants such as aberrant right subclavian artery, right-sided aortic arch, double aortic arch, left-sided superior vena cava |
| Posterior mediastinum | |
| Extramedullary haematopoiesis |
| Lymphadenopathy mediastinal |
| Neuroenteric cyst mediastinal |
| Neurogenic neoplasm mediastinal |
| Oesophageal abnormalities (achalasia oesophageal, oesophageal neoplasm, hiatal hernia |
| Paravertebral abnormalies (infectious, malignant and traumatic abnormalities of the thoracic spine) |
| Thyroid mass mediastinal |
| Vascular abnormalitites (aortic aneurysm, azygos continuation of the inferior vena cava, oesophageal varices |
CT is recommended as the primary imaging modality for assessing masses localized within the anterior and middle compartments of the mediastinum. It provides information on the precise location of the mass and its relationship to adjacent structures. It can determine whether the mass is cystic or solid, and whether it contains calcium or fat. Contrast enhancement provides information concerning the vascularization of the mass and its relationship with adjacent structures. Radioiodine scan is required if thyroid goitre is suspected. MRI is superior to contrast enhanced CT, however, in assessing the relationships of the mass to vascular structures and in determining vascular invasion. For masses localized in the posterior compartment of the mediastinum, MRI is preferentially used because of its superior ability in assessing the relationship of the mass to the adjacent spine. In case of suspicion of oesophageal abnormality, a barium swallow is indicated.
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