In many cases, non–contrast-enhanced CT is sufficient, but in others, contrast-enhanced CT can provide important information concerning enhancement of the mass and its relation to adjacent vascular structures. * I+ refers to contrast-enhanced chest CT. For masses localized within the anterior compartment of the mediastinum, computed tomography (CT) is a good diagnostic choice. Radiology department of the Rijnland Hospital in Leiderdorp, the Netherlands. Anterior Mediastinal Mass. A fat-fluid level is seen in 10% of cases and is highly specific for teratoma (Fig 16-8). A, The posteroanterior chest radiograph shows a large, anterior mediastinal mass. The thymus is an org… 16-5). The roles of computed tomography (CT) and magnetic resonance imaging (MRI) are also addressed. They include irregular tumor margins; invasion of surrounding mediastinal fat, vascular structures, or chest wall; and irregular interface with the adjacent lung. In some cases, imaging features enable the radiologist to make a specific diagnosis. Most patients are asymptomatic, but symptoms may arise from compression of the trachea or esophagus. Primary germ cell neoplasms (GCNs) arise from rests of primitive germ cells that were left within the mediastinum during their migration from the yolk sac to the urogenital ridge. The thymus reaches its maximum weight at puberty and subsequently undergoes fatty involution over a 5- to 15-year period. Acquired thymic cysts are most often associated with Hodgkin’s disease after radiation therapy. Thyroid mass: substernal goiter remains a significant consideration in the differential diagnosis of mediastinal masses, particularly those located in the anterior mediastinum… Log In or, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), DIAGNOSTIC IMAGING WORKUP OF MEDIASTINAL MASSES, Radiologic examination of a mediastinal mass usually can narrow the differential diagnosis to two or three likely candidates. Imaging plays a critical role in the identification and evaluation of mediastinal … They are often quite large at the time of presentation, and they may mimic cardiac enlargement on chest radiographs. A combined CT examination of the lower neck and chest is best (Fig. The most widely accepted classification scheme for thymic epithelial neoplasms is the World Health Organization (WHO) histologic classification that was published in 1999 and updated in 2004. Age: usually 40 to 60 years old; unusual in patients younger than 30 years old, Associations: myasthenia gravis, hypogammaglobulinemia, red cell aplasia, and stiff-person syndrome, Well-defined, round, soft tissue density mass with homogenous enhancement, Usually located anterior to the junction of the heart and great vessels, Irregularly marginated mass with necrotic components and heterogeneous enhancement, Additional findings of invasion of adjacent mediastinal vascular structures, chest wall invasion, or contiguous spread along pleural surfaces (usually unilaterally). 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. The mass contains foci of thyroid tissue that demonstrate intense enhancement and foci of low attenuation consistent with cysts. Approximately 40% of these patients present with enlargement of a single anterior mediastinal nodal group. The decision to obtain CT or MRI data depends on several factors, including the availability of MRI, patient factors (contraindication to intravenous contrast or MRI), and institutional practices. Types A and AB are usually encapsulated, type B (especially B3) has a greater likelihood of invasiveness, and type C is almost always invasive. Many thymic abnormalities can manifest as an anterior mediastinal mass, but the most common are thymic hyperplasia and thymic epithelial tumors. Thymic hyperplasia is usually identified on CT as enlargement of the thymus gland, which maintains its normal bilobed, arrowhead configuration (Fig. Teratomas usually are benign, but carcinoma may rarely develop within one of the germinal layer elements. Primary mediastinal lymphoma (Box 16-4) refers to malignant lymphoma that is exclusively or mostly limited to the mediastinum. It is anticipated that this system will improve lesion localization, help generate a focused differential diagnosis, and assist in tailoring biopsy and treatment plans. 16-4), and metastases outside of the thorax are rare. Seminomas appear as bulky, homogeneous anterior mediastinal masses, and calcification is rare. 16-1 and Box 16-1). Well-defined mass that extends from above the thoracic inlet, Displacement or compression of the trachea, Foci of calcification occasionally visible, Continuity with the cervical thyroid gland, Foci of high attenuation on noncontrast-enhanced images, Intense enhancement after intravenous contrast administration, Cystic areas and foci of calcification common. Configuration of the interface of the mass with adjacent lung is sometimes helpful. Robin Smithuis. Anterior mediastinal masses in the prevascular region can obliterate the anterior junction line, although it is usually the preservation of more posterior lines at radiography that helps identify the location of an anterior mediastinal mass. Anterior mediastinal masses generally arise from these structures. In this situation, a barium swallow should be obtained. Small masses may not be detectable on plain radiographs, but CT can help to identify a thymoma in patients with myasthenia gravis. Lymphadenopathy is infrequently detected on chest radiography but often is seen on CT. Sarcoidosis. Thymolipomas most often occur in younger patients and are usually identified on chest radiographs as incidental findings. MRI imaging using a chemical shift technique can reliably differentiate thymic hyperplasia from thymic neoplasms. Thymic involvement may occur in up to one third of patients with Hodgkin’s lymphoma. As their name suggests, they are confined to the anterior mediastinum, that portion of the mediastinum … Bilaterality of abnormality in proximity to the thoracic midline suggests a mediastinal origin. They include irregular tumor margins; invasion of surrounding mediastinal fat, vascular structures, or chest wall; and irregular interface with the adjacent lung. It provides information about the precise location of a mass and its relation to adjacent mediastinal … 16-1 and. 16-6). Masses appeared less homogeneous on MR images than on CT scans, and vascular compromise was better assessed with MR. Axial CT image of the chest at the level of the aortic arch (AA) shows enlargement of the thymus gland (arrows), which maintains its normal bilobed, arrowhead configuration. The normal contents of the anterior mediastinum include the thymus, lymph nodes, adipose tissue, nerves, vessels, and sometimes downward extension of the thyroid from the neck. mediastinal involvement not part of systemic disease) and the majority are Hodgkin lymphomas (~ 60%) 5. This is an update of the 2007 article, which used the Mountain-Dresler … CT is often required for detection and may provide specific diagnostic features or important staging information. B, Axial CT image of the chest (filmed using soft tissue windows) shows an anterior mediastinal mass (black arrows) and multiple, unilateral pleural masses (curved arrows). Thymic hyperplasia caused by hyperthyroidism. Calcification is most commonly observed in type B thymomas and type C thymic carcinoma. Axial, contrast-enhanced CT (, 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. 16-11), in contrast to most other causes of mediastinal masses, which usually manifest as a single mass. The algorithm presented in this chapter is a general guideline. If a dominant, solid soft tissue component is observed within the mass, a malignant GCN or a teratoma with malignant components should be considered in the diagnosis. Cardiopericardial abnormalities constitute an important pitfall in diagnosis of mediastinal masses. Mediastinal Masses Nature and Scope of the Problem. For masses localized within the anterior compartment of the mediastinum, computed tomography (CT) is a good diagnostic choice. They typically appear as heterogeneous, sharply marginated, multiloculated, cystic, anterior mediastinal masses. 16-2). 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