Thymic lymphoma usually manifests as a homogeneous, round mass with soft tissue density and without calcification. Nonvascular Mediastinal Masses Marilyn J. Siegel and Valerie Niehe Mallinckrodt Institute of Radiology, St. Louis, MO and the Medical Centre Haaglanden in the Hague, the Netherlands. 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. 16-4), and metastases outside of the thorax are rare. 16-1 and Box 16-1). A large round area of increased density indicates the presence of a soft tissue mass in the region of the left hilum; The left heart border (adjacent to the anterior mediastinum… Plain-film analysis of mediastinal masses is considered, with pointers for differential diagnosis. Anterior mediastinal masses consist of the 4 "T's" (Terrible lymphadenopathy, Thymic tumors, Teratoma, Thyroid mass… Evaluation of the mediastinum is an important part of the interpretation of a chest x-ray (CXR). The mediastinum is the most common location of an intrathoracic mass in children. Radiology of Mediastinal Masses Evaluation of the mediastinum is an important part of the interpretation of a chest x-ray (CXR). Age: young patients, usually in third decade, Gender: malignant germ cell neoplasms have marked male predominance, Heterogeneous, predominately cystic mass with solid components, Presence of fat is suggestive; identification of a tooth, although rare, is diagnostic. The diagnosis is often suspected on the basis of endocrine abnormalities in a patient with an anterior mediastinal mass. B, Sagittal MRI confirms the presence of a heterogeneous anterior mediastinal mass (long arrow) with invasion of the chest wall and extension into the presternal soft tissues (short arrow). The presence of enlarged mediastinal lymph nodes may suggest the diagnosis. Associated lymphadenopathy in other compartments of the mediastinum and associated extrathoracic lymphadenopathy each suggest the diagnosis of lymphoma. C, Axial, contrast-enhanced CT image at the level of the aortic arch shows the large, substernal component of the mass (arrows), which displaces the ascending aorta (A) and superior vena cava (S) posteriorly. A truly ectopic thyroid goiter is rare. PET is especially helpful in this setting because it can differentiate a residual, benign, fibrotic tissue mass from incompletely treated, viable tumor. 5 The prevascular (anterior) mediastinal … CT is often required for detection and may provide specific diagnostic features or important staging information. The mediastinum is the giant blind spot of the CXR. Background: Multiple different types of mediastinal masses may be encountered on imaging techniques in symptomatic or asymptomatic patients. There are a variety of benign and malignant GCNs (Box 16-5). 16-10). The anterior mediastinum is the most common extragonadal site of GCNs. A combined CT examination of the lower neck and chest is best (Fig. Imaging plays a critical role in the identification and evaluation of mediastinal … There are thymic lesions other than thymoma to consider, for example. MRI should be the first cross-sectional imaging study for patients with a suspected vascular abnormality who have a contraindication to intravenous contrast. The presence of fluid, calcium, soft tissue and/or fat in an anterior mediastinal mass on CT is highly suggestive of a mature teratoma. Figure 16-8 Teratoma. 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. Most patients are asymptomatic, but symptoms may arise from compression of the trachea or esophagus. Mediastinal masses in particular represent a significant challenge to the diagnostic capabilities of the radiologist. Superior mediastinal mass - Lymphoma. Axial, non–contrast-enhanced CT image shows discrete, round, soft tissue masses (arrows) in the anterior subcarinal region, consistent with enlarged lymph nodes. The thymus reaches its maximum weight at puberty and subsequently undergoes fatty involution over a 5- to 15-year period. 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. 16-5). In some cases, CT and MRI provide complementary information, and both may be indicated. Most thymomas are benign lesions confined within a fibrous capsule, but about 30% of thymomas are more aggressive and demonstrate invasion through the fibrous capsule. Thus, MR imaging is a completely noninvasive technique for the evaluation of mediastinal masses. Hodgkin disease has a bimodal age distribution, particularly affecting patients in their teens or 20s and those over age 50. Whereas anterior mediastinal masses from lymphoma typically demonstrate well-defined margins, invasion of adjacent lung parenchyma may result in irregular margins. Clinically, an anterior mediastinal mass … Mediastinal masses may be nonvascular or vascular masses and represent congenital anomalies, infections, benign and malignant neoplasms, and pseudomasses. Acquired thymic cysts are most often associated with Hodgkin’s disease after radiation therapy. There are a number of clinical conditions associated with thymoma, including myasthenia gravis (MG), pure red cell aplasia, and hypogammaglobulinemia. Most mediastinal masses of thyroid origin represent thyroid goiters, and they almost always extend inferiorly from the thyroid gland. In contrast, most other thymic abnormalities appear as a discrete mass rather than as uniform glandular enlargement. Thymolipoma is a rare, benign thymic neoplasm composed primarily of fat, but it also contains strands of thymic tissue. Thorough pathologic sampling is recommended to exclude small foci of immature tissue, other germ cell tumors, or carcinoma. The roles of computed tomography (CT) and magnetic resonance imaging (MRI) are also addressed. This area, called the mediastinum, is surrounded by the breastbone in front, the spine in back, and the lungs on each side. Thymic lymphoid hyperplasia is most commonly associated with myasthenia gravis. Although they are most commonly located anterior to the junction of the heart and great vessels, thymomas may occur at any level from the thoracic inlet to the diaphragm. Anterior mediastinal masses generally arise from these structures. Middle mediastinal lymphadenopathy is most reliably identified by the detection of a mass in an area that is known to have a specific lymph node—for example, a subcarinal, right paratracheal, azygos, or ductal node ( Fig 10.4 ).Because many of the processes to be considered involve multiple nodes in the same area, there is a strong but not invariable tendency for mediastinal … An important discriminating feature is the absence of calcification in untreated lymphoma. B, Axial, contrast-enhanced CT image reveals a round, anterior mediastinal mass with a partially calcified rim (right arrow) and a fat-fluid level (down arrow). Anterior mediastinal masses generally arise from these structures. Thymic lymphoid hyperplasia is a distinct entity that is characterized by an increased number of lymphoid follicles, but the gland is usually not enlarged. No general distinguishing demographic features, Single or multiple, round or elliptical masses located within known anatomic sites of lymph nodes, Often homogeneous, soft tissue density on CT but may have calcification, low-density centers, or vascular enhancement (see Box 16-9), Box 16-8 Mediastinal Lymphadenopathy Differential Diagnosis, Metastatic disease (bronchogenic carcinoma or extrathoracic primary*), Fungal infection (especially histoplasmosis), Viral infection (measles, infectious mononucleosis)†. Mediastinal masses instead have the shape of extraparenchymal masses, pushing toward lung with resultant obtuse angles (. Although the presence of calcification strongly suggests a diagnosis other than lymphoma, calcification frequently occurs in cases of treated lymphoma, but only rarely in untreated cases. It divides thymic epithelial neoplasms into three main groups: low-risk thymomas (types A, AB, and B1), high-risk thymomas (types B2 and B3), and thymic carcinomas, including neuroendocrine epithelial tumors (type C). The presence of an anterior mediastinal mass and unilateral pleural masses strongly suggests invasive thymoma. ■ Recognize the MR imaging features of benign or “don’t touch” lesions. On imaging studies, the thymus gland usually appears normal, but it may uncommonly may appear as a focal mass or diffuse glandular enlargement. Mediastinal seminomas are usually radiosensitive, and patients have an overall survival rate of about 75%. Because of the geometry of the mediastinum most of these masses will be located in the anterior mediastinum. 1- Lymph nodes enlargement. Mediastinal mass may be caused by a wide variety of neoplastic and non-neoplastic pathologies. Right parasagittal, T1-weighted MRI shows a homogeneous mass, Neoplastic, inflammatory, or infectious lymphadenopathy (Box 16-7) is the most common cause of a middle mediastinal mass (, Mediastinal Lymphadenopathy Differential Diagnosis, Metastatic disease (bronchogenic carcinoma or extrathoracic primary, Viral infection (measles, infectious mononucleosis). A radioiodine scan may be confirmatory, with demonstration of radioiodine uptake from foci of functioning thyroid tissue within the mass. Pleural dissemination, also referred to as, Thymic Hyperplasia: Associated Systemic Abnormalities. A soft tissue mass widens the superior mediastinum; The mass … Pleural dissemination, also referred to as drop metastases, and pericardial involvement are common, whereas lung metastases are rare. Robin Smithuis. Seminomas appear as bulky, homogeneous anterior mediastinal masses, and calcification is rare. Imaging features vary, ranging from a single, spherical soft tissue mass in the anterior mediastinum to a large, lobulated mass representing a conglomeration of lymph nodes. Correlative nuclear medicine gallium imaging may be helpful because most Hodgkin’s lymphomas take up gallium avidly. This is known as the hilum overlay sign. In some cases, imaging features enable the radiologist to make a specific diagnosis. Thymic hyperplasia is usually identified on CT as enlargement of the thymus gland, which maintains its normal bilobed, arrowhead configuration (Fig. When there is a mediastinal mass and you still can see the hilar vessels through this mass, then you know the mass does not arise from the hilum. 3. 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. Thymic carcinoid tumor is rare and is thought to arise from thymic cells of neural crest origin. However, most other anterior mediastinal masses are located anterior to the great vessels, and a mediastinal mass located anterior to the great vessels in a retrosternal location is unlikely to be of thyroid origin. The thymus is an org… The mass contains foci of thyroid tissue that demonstrate intense enhancement and foci of low attenuation consistent with cysts. Characteristic CT imaging features include a well-defined, round, or oval mass, usually of homogeneous soft tissue density, that is located within the anterior mediastinum (Fig. 16-11), in contrast to most other causes of mediastinal masses, which usually manifest as a single mass. The first part is to determine that a mass is actually mediastinal, and the second part is to place it in the anterior, middle, or posterior mediastinum. A combination of fluid, fat, and calcification is frequently observed. Many thymic abnormalities can manifest as an anterior mediastinal mass, but the most common are thymic hyperplasia and thymic epithelial tumors. Invasive thymomas typically spread locally (Fig. Mediastinal masses … This is an update of the 2007 article, which used the Mountain-Dresler … CT is the preferred imaging modality for further evaluation of a middle mediastinal mass. Only 10% of lymphomas which involve the mediastinum are primary (i.e. ■ Identify key components of noncardiac and nonvascular MR imaging protocols. In about 20% of cases, there is evidence of calcification, which is typically curvilinear. However, thymomas may be associated with other abnormalities, including myasthenia gravis, red cell aplasia, hypogammaglobulinemia, and stiff-person syndrome. Age: mostly young adults, but Hodgkin’s lymphoma has a bimodal distribution, with initial peak in young adults and a second peak after age 50 years, Gender: female predominance, except for lymphoblastic lymphoma, Variable appearance, ranging from a single, spherical soft tissue mass to a large, lobulated mass, Mass may have homogeneous or heterogeneous soft tissue attenuation. Thyroid mass: substernal goiter remains a significant consideration in the differential diagnosis of mediastinal masses, particularly those located in the anterior mediastinum… Tumors (also called neoplasms) are masses of cells. Figure 16-10 Thyroid goiter. Turning to clinical clues, teratoma is typically a disease of teenagers, whereas thymoma usually affects those aged 40 to 60 years. Abstract Anterior mediastinal masses are detectable on chest x-rays when they distort the normal mediastinal contours or fill the retrosternal clear space on the lateral view. In patients with prior neck exploration and continued primary hyperparathyroidism, the incidence of mediastinal adenoma is 47%, and 17% of such glands cannot be reached from a neck incision. Lymphomas are responsible for approximately 15% of all primary mediastinal masses, and 45% of anterior mediastinal masses in children 1. Figure 16-5 Thymic hyperplasia caused by hyperthyroidism. The radiologic workup depends on the location of the mass (Fig. Thymic carcinoid demonstrates some of the same features as bronchial carcinoid (. The mediastinum contains the heart, aorta, esophagus, thymus, trachea, lymph nodes and nerves. In contrast, most other thymic abnormalities appear as a discrete mass rather than as uniform glandular enlargement. MRI imaging using a chemical shift technique can reliably differentiate thymic hyperplasia from thymic neoplasms. It is helpful to identify the location of the mass since this significantly reduces the breadth of the … The superior extent of the mass (upper white arrow) extends above the thoracic inlet and is associated with rightward deviation of the trachea (black arrows). They include irregular tumor margins; invasion of surrounding mediastinal fat, vascular structures, or chest wall; and irregular interface with the adjacent lung. It is anticipated that this system will improve lesion localization, help generate a focused differential diagnosis, and assist in tailoring biopsy and treatment plans. 2- Aortic … C, Axial CT image of the chest (filmed using lung windows) shows multiple pleural masses (curved arrows), including a pleural mass within the minor fissure (open arrow). Although the true prevalence of mediastinal masses is not known, a 0.9% prevalence of anterior or prevascular mediastinal masses was found among the 2,571 chest CTs of the 51% female cohort of the Framingham Heart Study, with a mean age of 59 years . They can be benign (not cancer) or malignant (cancer). A, The lateral chest radiograph shows increased opacity in the normally clear retrosternal space, with a well-defined, round border inferiorly (arrow). Box 16-9 Mediastinal Lymphadenopathy: Characteristic Features, Mycobacterium avium-intracellulare (MAI)*, Only gold members can continue reading. 16-6). Thymic hyperplasia (Box 16-3) is associated with a wide variety of systemic abnormalities, including hyperthyroidism. Localization of mediastinal masses on CXR is a two-part job. The “4 Ts” delineate the important entities in anterior mediastinal mass differential diagnosis—thymoma, thyroid, teratoma, and terrible lymphoma. They typically appear as heterogeneous, sharply marginated, multiloculated, cystic, anterior mediastinal masses. ■ Use MR imaging to answer questions regarding local invasion and extent of disease in the thorax. Methods: Radiological compartmentalisation of the mediastinum helps in focusing the diagnosis of masses … Identification of these lymph node characteristics can shorten the lengthy differential diagnosis of mediastinal lymphadenopathy (Box 16-9). 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. Box 16-3 Thymic Hyperplasia: Associated Systemic Abnormalities. Because thyroid goiters account for most mediastinal masses of thyroid origin, the demographics of thyroid mediastinal masses are similar to those of thyroid goiter, with a tendency to occur predominately in middle-aged women. The radiologic presentation of most neural tumors is a homogeneous opaque mass in the posterior mediastinum. 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. Thymic cysts may be congenital or acquired. When there is a mediastinal mass and you still can see the hilar vessels through this mass, then you know the mass does not arise from the hilum. mediastinal involvement not part of systemic disease) and the majority are Hodgkin lymphomas (~ 60%) 5. 16-7). Configuration of the interface of the mass with adjacent lung is sometimes helpful. The system used by Felson (, For anterior mediastinal masses, the classic differential diagnosis is the “4 Ts”: thymoma, thyroid, teratoma, and terrible lymphoma (. C, Axial noncontrast CT scan shows destruction of the sternum (black arrow) by the anterior mediastinal mass (white arrows). AA, ascending aorta; DA, descending aorta. Mediastinal masses are stratified by mediastinal compartment, as recently re-defined by the International Thymic Malignancy Interest Group (ITMIG) on the basis of CT, rather than chest radiography (CXR). It is therefore no surprise that there are no distinguishing demographic features. Axial CT image of the chest shows a right cardiophrenic angle mass, which is predominately fat attenuation. Middle mediastinal masses The middle mediastinal masses widened the para-tracheal stripes, displaced the azygo-oesophageal recess on right side. Henschke et al reported a prevalence of prevascular (or anterior mediastinal) masses of 0.4% in 9,263 high-risk smokers over the age of 40 who were evaluated as part of the Early Lung Cancer Action Project ; masses … Several types of malignant GCNs occur within the anterior mediastinum, including pure seminomas and several nonseminomatous tumors (i.e., choriocarcinoma; embryonal cell carcinoma, yolk sac tumors, and mixed GCNs). 16-9), although MRI can be used (, Thyroid goiter. Notice the thin strands of soft tissue attenuation (arrow) within the mass, representing strands of thymic tissue, and the foci of calcification. Extrathoracic primaries that commonly metastasize to mediastinal lymph nodes include genitourinary tumors, head and neck carcinomas, thyroid carcinomas, melanoma, and breast carcinoma. Figure 16-4 Invasive thymoma. the anterior mediastinum include the thymus, lymph nodes, adipose tissue, nerves, vessels, and sometimes downward extension of the thyroid from the neck. 16-5). * Extrathoracic primaries that commonly metastasize to mediastinal lymph nodes include genitourinary tumors, head and neck carcinomas, thyroid carcinomas, melanoma, and breast carcinoma. The mass extends inferiorly to the level of the base of the heart (lower white arrows). Thymic hyperplasia is usually identified on CT as enlargement of the thymus gland, which maintains its normal bilobed, arrowhead configuration (Fig. Calcification is most commonly observed in type B thymomas and type C thymic carcinoma. 2. Figure 16-1 Mediastinal compartments. Identification of fat within the mass on CT or MRI suggests the diagnosis (Fig. Radiographically, a thymic cyst usually appears as a well-defined, cystic mass with an imperceptible wall. For masses localized within the anterior compartment of the mediastinum, computed tomography (CT) is a good diagnostic choice. Posterior mediastinal mass. Seventy percent of GCNs are benign, comprising mostly teratomas and dermoid cysts. Mediastinal Masses Nature and Scope of the Problem. The differential diagnosis for cystic masses of the mediastinum include: bronchogenic cyst esophageal duplication cyst neuroenteric cyst pericardial cyst meningocele lymphangioma thymic cyst cystic teratoma of mediastinum … Invasive thymomas typically spread locally (Fig. After completing this journal-based SA-CME activity, participants will be able to: 1. In contrast, patients with malignant GCNs usually have a poor prognosis, with the exception of those with seminoma. CT can also determine whether a mass is cystic or solid and whether it contains calcium or fat. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) is of limited value in differentiating thymic hyperplasia from thymic neoplasms because both may demonstrate FDG avidity. For example, a small, smooth, round, homogeneous anterior mediastinal mass usually corresponds to a type A thymoma, whereas irregular contours and heterogeneous attenuation favor a type C thymic carcinoma (Fig. Saying that it is important is not the same as saying that it is well done. The association with myasthenia gravis is the most common of the three; about 15% of patients with myasthenia gravis have a thymoma, and about 50% of patients with thymomas have myasthenia gravis. A combined CT examination of the lower neck and chest is best (Fig. A testicular exam and scrotal ultrasound is recommended when a mediastinal mass … The classic mnemonic is not all inclusive. CT plays a role in detecting and characterizing lymph nodes. An exception occurs when a posterior mediastinal mass is suspected to be of esophageal origin. Figure 16-9 Thyroid goiter. 127 , 459 Calcification should be evenly distributed through a mass … Mediastinal masses are usually found "incidentally" by radiologic methods such as chest x-rays, computed tomography (CT), or magnetic resonance imaging (MRI) that was being done for other reasons. An anterosuperior mediastinal mass can be caused by neoplastic and non-neoplastic pathology. CT may show a mass with homogeneous soft tissue density, or it may appear heterogeneous, in which the low-attenuation areas represent necrosis. Thymomas account for most anterior mediastinal masses in adults and typically occur as incidental findings in otherwise healthy individuals.
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