Chapter 16 Mediastinal Masses
DIAGNOSTIC IMAGING WORKUP OF MEDIASTINAL MASSES
Radiologic examination of a mediastinal mass usually can narrow the differential diagnosis to two or three likely candidates. In some cases, imaging features enable the radiologist to make a specific diagnosis. The radiologic workup depends on the location of the mass (Fig. 16-1 and Box 16-1).
Box 16-1 Algorithm for Imaging Evaluation of Mediastinal Masses
Mediastinal mass detected on chest radiograph | ||
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Chest CT | Chest CT (I+)* | MRI or Barium swallow if esophageal origin is suspected |
Other studies:Gallium scan if Hodgkin’s lymphoma is suspectedRadioiodine scanif thyroid goiter issuspected | Other studies:MRI if there is acontraindicationto contrast and avascular abnormalityis suspected or ifvascular invasionis suspected |
ANTERIOR MEDIASTINAL MASSES
Thymic Abnormalities
Thymic Epithelial Tumors
Box 16-2 Thymoma
DEMOGRAPHICS
Age: usually 40 to 60 years old; unusual in patients younger than 30 years old
Gender: men and women equally affected
Associations: myasthenia gravis, hypogammaglobulinemia, red cell aplasia, and stiff-person syndrome
When interpreting CT scans or MRI studies of patients with suspected or proven thymic neoplasms, signs of capsular invasion or extracapsular extension should be carefully sought. They include irregular tumor margins; invasion of surrounding mediastinal fat, vascular structures, or chest wall; and irregular interface with the adjacent lung. Invasive thymomas typically spread locally (Fig. 16-4), and metastases outside of the thorax are rare. Pleural dissemination, also referred to as drop metastases, and pericardial involvement are common, whereas lung metastases are rare. The extent of involvement by thymic neoplasms is often best determined by viewing CT or MRI data in axial, sagittal, and coronal planes rather than relying solely on axial images (see Fig. 16-3).
Primary Mediastinal Lymphoma
Box 16-4 Primary Mediastinal Lymphoma
Germ Cell Neoplasms
Box 16-5 Germ Cell Neoplasms
DEMOGRAPHICS
Age: young patients, usually in third decade
Gender: malignant germ cell neoplasms have marked male predominance
Thyroid Abnormalities
BOX 16-6 Thyroid Masses
The most important of these features is demonstration of continuity of the mass with the cervical thyroid gland. A combined CT examination of the lower neck and chest is best (Fig. 16-9), although MRI can be used (Fig. 16-10). A radioiodine scan may be confirmatory, with demonstration of radioiodine uptake from foci of functioning thyroid tissue within the mass.
MIDDLE MEDIASTINAL MASSES
Lymphadenopathy
Neoplastic, inflammatory, or infectious lymphadenopathy (Box 16-7) is the most common cause of a middle mediastinal mass (Box 16-8). It is therefore no surprise that there are no distinguishing demographic features.
Box 16-8 Mediastinal Lymphadenopathy Differential Diagnosis
INFECTIOUS CAUSES
Fungal infection (especially histoplasmosis)
Viral infection (measles, infectious mononucleosis)†
