Approaching the Patient with an Anterior Mediastinal Mass: A Guide for Radiologists
2014; Elsevier BV; Volume: 9; Issue: 9 Linguagem: Inglês
10.1097/jto.0000000000000295
ISSN1556-1380
AutoresBrett W. Carter, Meinoshin Okumura, Frank Detterbeck, Edith M. Marom,
Tópico(s)Neurofibromatosis and Schwannoma Cases
ResumoMediastinal masses are relatively uncommon, yet include a large variety of entities. Some tumors can be diagnosed with confidence based on imaging alone; others when a typical appearance is combined with the right clinical presentation. A structured approach for radiologists is presented to facilitate evaluation of patients with anterior mediastinal tumors. The approach focuses first on the more common tumors and on imaging features that strongly suggest a particular diagnosis. Discussion with the clinician can be very helpful in formulating a presumptive diagnosis. This article also discusses that confirmatory imaging or biopsy tests are most beneficial in particular situations. Mediastinal masses are relatively uncommon, yet include a large variety of entities. Some tumors can be diagnosed with confidence based on imaging alone; others when a typical appearance is combined with the right clinical presentation. A structured approach for radiologists is presented to facilitate evaluation of patients with anterior mediastinal tumors. The approach focuses first on the more common tumors and on imaging features that strongly suggest a particular diagnosis. Discussion with the clinician can be very helpful in formulating a presumptive diagnosis. This article also discusses that confirmatory imaging or biopsy tests are most beneficial in particular situations. Mediastinal masses are relatively uncommon. Furthermore, because there is such a wide variety of pathologic entities that can occur in this region, the average radiologist or clinician will encounter many of these specific lesions only infrequently. Imaging is a critical part of establishing a presumptive diagnosis, which will guide whether and what type of confirmatory testing is needed. When classic features are present, a presumptive diagnosis can be made with a high degree of confidence based on imaging alone. However, the appearance of anterior mediastinal lesions is often less specific. Nevertheless, when combined with a typical clinical presentation, a particular entity can be strongly suggested. Developing an appropriate differential diagnosis for a particular patient can be very useful in avoiding unnecessary and sometimes misleading biopsies or additional tests. A framework to guide the image interpretation and additional testing improves the efficiency of the evaluation. This is particularly pertinent since incidental anterior mediastinal abnormalities are discovered with increasing frequency due to increased imaging of asymptomatic patients, either for screening or staging of extrathoracic primary malignancies.1Henschke CI Lee IJ Wu N et al.CT screening for lung cancer: prevalence and incidence of mediastinal masses.Radiology. 2006; 239: 586-590Crossref PubMed Scopus (97) Google Scholar To address this need, the International Thymic Malignancy Interest Group (ITMIG) began an initiative to develop such a structured approach. This article represents the output of this project primarily addressed to radiologists; a companion paper focused on the clinician has also been produced.2Carter BW Marom EM Detterbeck FC Approaching the patient with an anterior mediastinal mass: a guide for clinicians.J Thorac Oncol. 2014; Google Scholar The algorithm outlined in this document represents a consensus among radiologists and clinicians with a particular interest in anterior mediastinal diseases. The ITMIG Education Committee assembled a core workgroup (E.M.M., B.W.C., F.D., and M.O.) to review the existing literature as well as standards for imaging and clinical investigation of patients with an anterior mediastinal mass. This group drafted a proposed approach to the patient presenting with an anterior mediastinal mass. The document was then refined by an extended workgroup (Ami Rubinowitz, Wentao Fang, Jeanne B. Ackman, and Stephen Cassivi). Slightly more than half of all mediastinal masses are located in the anterior mediastinum. One-fourth of mediastinal masses are discovered in the middle mediastinum, and another one-fourth of masses are found in the posterior mediastinum.3Davis Jr, RD Oldham Jr, HN Sabiston Jr., DC Primary cysts and neoplasms of the mediastinum: recent changes in clinical presentation, methods of diagnosis, management, and results.Ann Thorac Surg. 1987; 44: 229-237Abstract Full Text PDF PubMed Scopus (328) Google Scholar, 4Levasseur P Kaswin R Rojas-Miranda A et al.Apropos of a series of 742 operated patients.Nouv Presse Med. 1976; 5: 2857-2859PubMed Google Scholar, 5Cohen AJ Thompson L Edwards FH Bellamy RF Primary cysts and tumors of the mediastinum.Ann Thorac Surg. 1991; 51 (discussion 385): 378-384Abstract Full Text PDF PubMed Scopus (120) Google Scholar, 6Rubush JL Gardner IR Boyd WC Ehrenhaft JL Mediastinal tumors. Review of 186 cases.J Thorac Cardiovasc Surg. 1973; 65: 216-222PubMed Google Scholar, 7Wychulis AR Payne WS Clagett OT Woolner LB Surgical treatment of mediastinal tumors: a 40 year experience.J Thorac Cardiovasc Surg. 1971; 62: 379-392PubMed Google Scholar, 8Mullen B Richardson JD Primary anterior mediastinal tumors in children and adults.Ann Thorac Surg. 1986; 42: 338-345Abstract Full Text PDF PubMed Scopus (178) Google Scholar, 9Takeda S Miyoshi S Minami M et al.Clinical spectrum of primary mediastinal tumors: a comparison of adult and pediatric populations (Abstract).Chest. 2000; 118: 206SGoogle Scholar, 10Whooley BP Urschel JD Antkowiak JG Takita H Primary tumors of the mediastinum.J Surg Oncol. 1999; 70: 95-99Crossref PubMed Scopus (58) Google Scholar, 11Azarow KS Pearl RH Zurcher R Edwards FH Cohen AJ Primary mediastinal masses. A comparison of adult and pediatric populations.J Thorac Cardiovasc Surg. 1993; 106: 67-72PubMed Google Scholar Assignment of lesions to particular mediastinal compartments has been quite useful in narrowing the differential diagnosis. In the past, this classification was based on varying definitions based on the lateral chest radiograph. A modern, computed tomography (CT)-based definition of mediastinal compartments has been developed by ITMIG12Carter BW Tomiyama N Bhora FY et al.A modern definition of mediastinal compartments.J Thorac Oncol. 2014; 9: S99-S103Google Scholar building upon work done by radiologists associated with the Japanese Association for Research in the Thymus.13Fujimoto K Hara M Tomiyama N Kusumoto M Sakai F Fujii Y Proposal for a new mediastinal compartment classification of transverse plane images according to the Japanese Association for Research on the Thymus (JART) General Rules for the Study of Mediastinal Tumors.Oncol Rep. 2014; 31: 565-572PubMed Google Scholar The most common tumors of the anterior mediastinum include thymic malignancies and lymphoma, but the prevalence of the different abnormalities varies markedly according to both age and gender. Thymoma is the most common anterior mediastinal mass and primary tumor of the anterior mediastinum, with the highest incidence in middle aged patients. Other tumors of the anterior mediastinum include benign teratomas and malignant germ cell tumors such as seminomas and nonseminomatous germ cell tumors (NSGCTs). Malignant teratomas, which are residual lesions after treatment of NSGCTs, are typically grouped in the same category as NSGCTs. Thymic cysts and benign cystic lesions (usually acquired, often related to surgery and radiation therapy) are among the most common nonneoplastic lesions of the anterior mediastinum. Additional nonneoplastic masses include vascular abnormalities, substernal extension of thyroid goiters, other cystic lesions such as pericardial or bronchogenic cysts, and lesions related to infection such as tuberculosis. The true incidence of anterior mediastinal masses is difficult to ascertain from the existing literature for numerous reasons. One of the most important of these is that different clinical and/or radiologic classification schemes have been used to define the mediastinal compartments. Additionally, the inclusion of nonneoplastic lesions such as thymic and pericardial cysts differs between series. Finally, there is variability in the inclusion of lymphomas in different series. More detail on the relative incidence of anterior mediastinal tumors is provided elsewhere.2Carter BW Marom EM Detterbeck FC Approaching the patient with an anterior mediastinal mass: a guide for clinicians.J Thorac Oncol. 2014; Google Scholar A large anterior mediastinal mass is readily identified by chest radiography as it typically manifests as an extra soft tissue mass or opacity. The use of the silhouette sign, which describes the loss of normal borders of intrathoracic structures, increases the sensitivity of detecting mediastinal abnormalities. The borders of the anterior mediastinum, that is, the ascending aorta, right and left heart border, are visualized by radiography because they are delineated by natural contrast: the air containing lung (Figure 1A). The density of soft tissue masses is similar to the anterior mediastinal structures and the image produced by the X-rays cannot differentiate between the abnormal mass and the normal mediastinal structure. However, since the mass displaces the air-containing lung from the normal mediastinal structure, the border of the normal mediastinal structure is lost. This loss of normal border is termed the silhouette sign (Figure 1B). However, the identification of a small mediastinal mass requires a more methodical approach. The presence of the anterior junction line, representing the point of contact between the anterior lungs and their pleural surfaces anterior to the cardiovascular structures, can help exclude the presence of an anterior mediastinal mass. This line is seen in 20% of normal chest radiographs (Figure 2A). Thickening of this line indicates an anterior mediastinal mass (Figure 2B).FIGURE 2Normal and abnormal anterior junction line. A, Coned-down posteroanterior chest radiograph demonstrates the normal anterior junction line (arrows), representing the point of contact between the anterior lungs and their pleural surfaces anterior to the cardiovascular structures. B, Coned-down posteroanterior chest radiograph of a different patient demonstrates thickening of the anterior junction line (arrows) consistent with a biopsy-proven thymoma in the anterior mediastinum.View Large Image Figure ViewerDownload (PPT) Once an abnormality is identified by chest radiography, cross-sectional imaging is used to characterize the lesion, generate a differential diagnosis, assess for other abnormalities, and guide further management. CT with intravenous (IV) contrast has traditionally been the imaging modality of choice in the evaluation and characterization of an anterior mediastinal mass. One study analyzing 127 anterior mediastinal masses of various etiologies demonstrated that CT was equal or superior to magnetic resonance imaging (MRI) in the diagnosis of anterior mediastinal masses except for thymic cysts.14Tomiyama N Honda O Tsubamoto M et al.Anterior mediastinal tumors: diagnostic accuracy of CT and MRI.Eur J Radiol. 2009; 69: 280-288Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar Indeed, when a cystic mass is suspected or is to be investigated, MRI is the most useful imaging modality, because MRI is superior to CT in distinguishing cystic from solid masses (e.g., thymic cysts from thymic neoplasms), discerning cystic/necrotic components within solid masses, and discerning thymic hyperplasia from thymic tumors.15Ackman JB Wu CC MRI of the thymus.AJR Am J Roentgenol. 2011; 197: W15-20Crossref PubMed Scopus (52) Google Scholar For patients unable to undergo contrast-enhanced CT due to renal failure or allergy to IV contrast, non-contrast MRI may be performed to characterize the lesion and evaluate for involvement of vascular structures. Chemical shift techniques used in MRI can also be used to differentiate thymic hyperplasia from thymoma in adult patients.16Inaoka T Takahashi K Mineta M et al.Thymic hyperplasia and thymus gland tumors: differentiation with chemical shift MR imaging.Radiology. 2007; 243: 869-876Crossref PubMed Scopus (73) Google Scholar,17Takahashi K Al-Janabi NJ Computed tomography and magnetic resonance imaging of mediastinal tumors.J Magn Reson Imaging. 2010; 32: 1325-1339Crossref PubMed Scopus (119) Google Scholar 18Rosado-de-Christenson ML Templeton PA Moran CA From the archives of the AFIP.Mediastinal germ cell tumors: radiologic and pathologic correlation Radiographics. 1992; 12: 1013-1030Google Scholar F-FDG positron emission tomography (PET)/CT is not routinely performed to evaluate or characterize an anterior mediastinal mass, but may be used to stage patients with specific malignant lesions and monitor response to therapy and in some cases can help distinguish between certain malignancies. However, it is important to note that imaging with FDG-PET can be misleading, given that normal and hyperplastic thymus and inflammatory lesions in the mediastinum are often FDG-avid. Evaluation of an anterior mediastinal mass may seem difficult because of the number of different entities and the rarity with which most of them are encountered by the average radiologist. A discussion between the clinician and the radiologist is exceedingly important, and it is best if this happens at the time the images are interpreted. The degree of confidence in the presumptive diagnosis depends on how well it fits from a variety of viewpoints (imaging, demographics, and clinical presentation) and has significant bearing on the need for biopsy and if so, which type of biopsy approach is best. To structure the approach to patients with an anterior mediastinal mass, we begin with identification of certain imaging characteristics that allow a fairly certain diagnosis to be made on imaging alone. Then we discuss imaging features that are fairly common, and, while not definite by imaging appearance alone, can nevertheless lead to a fairly reliable presumptive diagnosis in the appropriate clinical setting. We focus initially on the more commonly seen features and tumors, in order to present a practical way of structuring an approach to patients. Unusual tumors and features are discussed last; because of the rarity of such tumors the degree of certainly of the presumed diagnosis will always be somewhat limited. A highly reliable clinical diagnosis of an anterior mediastinal lesion can be made when certain characteristic features are found on cross-sectional imaging and/or are noted in the clinical presentation (Table 1). Specific findings such as hyperdense and enhancing lesions that communicate with the thyroid gland, intralesional fat, cystic components, and soft tissue attenuation may be used to narrow the differential diagnosis. The presence of calcifications, whether punctate, coarse, or curvilinear, cannot discriminate benign from malignant anterior mediastinal masses and may be seen in a benign lesion (such as a benign teratoma) as well as in a malignant lesion (such as a thymoma or treated lymphoma).18Rosado-de-Christenson ML Templeton PA Moran CA From the archives of the AFIP.Mediastinal germ cell tumors: radiologic and pathologic correlation Radiographics. 1992; 12: 1013-1030Google ScholarTABLE 1Imaging Algorithm for Anterior Mediastinal Masses% of Anterior Mediastinal MassesLevel of ConfidenceDiagnosed WithaThis refers to which factors play a prominent role in establishing the presumptive clinical diagnosis.Confirm With/Next StepsHighly Characteristic LesionsHyperdense and enhancing lesion with connection to thyroid → Goiter20-40% age >40CertainImaging−Heterogeneous with fat, fluid, soft tissue, & calcification → Benign teratoma25% age 10-19Very highImaging−10-15% age 20-49Well-circumscribed, round/oval/saccular, and homogeneous mass located near thymic bed on CT → Consider thymic cyst and evaluate with MRI If purely cystic → Thymic cyst and follow-up with MRI<5%Very highImagingMRI If cystic but with soft tissue components → Multilocular cyst or cystic thymoma 40 Context: Pt with Myasthenia gravis or other paraneoplastic syndrome5-10% age 20-39Certain+Clinical± Biopsy∼20% age >40Multiple markedly enlarged or matted lymph nodes / masses in anterior mediastinum ± neck, ± encasing but respecting vessels → HD, MLC- NHL20-50% ♀ age <40HighImagingCore biopsy20-25% ♂ age <40 40 Context: "B" symptoms and ↑ LDHSameVery high+ ClinicalCore biopsyLarge mass with pleural effusion, rapid onset, "B" symptoms → LB-NHL15% age 10-19HighImaging,Cytology5-10% age 20-39ClinicalLarge heterogeneous mass, especially with lung metastases → NSGCT10-25% ♂ age <40ModerateImaging,Labs, Context: Young 3 with rapid onset of symptoms< 5% ♂ age >40Clinical± biopsy2-5% ♀ age <40Homogeneous or slightly hetrogeneous mass ± lung metastases → Seminoma5-10% ♂ age <40ModerateImaging,Biopsy Context:: young ♂, intermediate onset0-2% ♀ age <40ClinicalLarge heterogeneous mass, local invasion, lymphadenopathy, ± distant metastases → Thymic carcinoma or carcinoid 40Low attenuation, symmetric enlargement of thymus Context:: Pt treated with chemo, RT, or steroids → Thymic hyperplasiaUncommonVery highClinical, Imaging± MRIRare Characteristic FeaturesLobular, homogeneous or slightly heterogeneous mass and with subpleural implants → Thymoma (invasive)<5%Very highImagingBiopsyLarge fatty mass with small amount of soft tissue & vessels, connection with thymus → Thymolipoma<5%Very highImaging−Lobulated, encapsulated lesion consisting almost entirely of fat → Lipoma2%Very highImaging−Fatty lesion with aggressive features such as soft tissue components, invasion, lymphadenopathy, or metastatic disease → LiposarcomaVery rareModerateImagingBiopsyA proposed structured approach for radiologists in evaluating patients with an anterior mediastinal mass. This table focuses on the most common entities first and on entities in which imaging is often particularly helpful. However, the incidence varies according to age and gender, and the level of confidence in a presumptive clinical diagnosis varies according to whether the radiographic features are seen with a congruent clinical setting."B" symptoms, fever, sweats, and weight loss; HD, Hodgkin disease; LB-NHL, lymphoblastic non-Hodgkin lymphoma; LDH, lactose dehydrogenase; MLC-NHL, mediastinal large cell non-Hodgkin lymphoma; MRI, magnetic resonance imaging; NSGCT, nonseminomatous germ cell tumor.a This refers to which factors play a prominent role in establishing the presumptive clinical diagnosis. Open table in a new tab A proposed structured approach for radiologists in evaluating patients with an anterior mediastinal mass. This table focuses on the most common entities first and on entities in which imaging is often particularly helpful. However, the incidence varies according to age and gender, and the level of confidence in a presumptive clinical diagnosis varies according to whether the radiographic features are seen with a congruent clinical setting. "B" symptoms, fever, sweats, and weight loss; HD, Hodgkin disease; LB-NHL, lymphoblastic non-Hodgkin lymphoma; LDH, lactose dehydrogenase; MLC-NHL, mediastinal large cell non-Hodgkin lymphoma; MRI, magnetic resonance imaging; NSGCT, nonseminomatous germ cell tumor. A heterogeneous anterior mediastinal mass that is intrinsically hyperdense, enhances following the administration of IV contrast, and demonstrates continuity with the cervical thyroid gland can reliably be diagnosed as a mediastinal goiter. Most mediastinal goiters demonstrate high attenuation on non-contrast CT, with Hounsfield Units measuring 70–85, due to the presence of iodine (Figure 3A). Following the administration of IV contrast, prolonged and sustained enhancement is typically seen. Regions of low attenuation within goiters are commonly seen and represent cystic changes. Calcifications may also be present. The majority of substernal goiters can be reliably diagnosed by CT imaging alone. However, it is important to note that mediastinal goiters are not always connected to the thyroid gland; nevertheless, when they are separate, they often demonstrate similar imaging features. As thyroid goiters may result in compression and deviation of the trachea, evaluation of the airways should be performed. When a goiter exhibits loss of distinct mediastinal fascial planes or is associated with cervical or mediastinal lymphadenopathy, the possibility of thyroid malignancy should be investigated.19Naidich DP Webb WR Muller NL Krinsky GA Zerhouni EA Siegelman SS Mediastinum. Computed Tomography and Magnetic Resonance of the Thorax. 3rd Ed. Lippincott Williams and Wilkins, Philadelphia, PA1999: 82-83Google Scholar Although patients may be asymptomatic, symptoms related to compression of mediastinal structures (particularly the airways) should be reported. The presence of visible areas of intralesional fat (which typically measures between −40 and −120 Hounsfield Units on CT) within a heterogeneous anterior mediastinal mass is highly suggestive of a benign teratoma, as these lesions characteristically demonstrate varying amounts of fat, fluid, calcification (including bone and tooth-like elements), and soft tissue.20Molinari F Bankier AA Eisenberg RL Fat-containing lesions in adult thoracic imaging.AJR Am J Roentgenol. 2011; 197: W795-W813Crossref PubMed Scopus (0) Google Scholar,21Rosado-de-Christenson ML Templeton PA Moran CA From the archives of the AFIP.Mediastinal germ cell tumors: radiologic and pathologic correlation Radiographics. 1992; 12: 1013-1030Google Scholar Fat is identified in approximately 50% of cases21Rosado-de-Christenson ML Templeton PA Moran CA From the archives of the AFIP.Mediastinal germ cell tumors: radiologic and pathologic correlation Radiographics. 1992; 12: 1013-1030Google Scholar (Figure 3B). Although a fat–fluid level is highly specific for teratoma, this finding is much less common, and formation of bone or a tooth is rare.22Wright C Pearson F Cooper J Deslauriers J Ginsberg RJ Hiebert C Patterson G Urschel H Germ cell tumors of the mediastinum. Thoracic Surgery. Churchill Livingstone, New York2002: 1711Google Scholar Benign teratomas can sometimes be mostly cystic. Most benign teratomas are sufficiently characteristic to be diagnosed reliably based on imaging characteristics alone by an experienced thoracic radiologist. Benign teratomas are typically seen in younger patients and account for approximately 25% of anterior mediastinal masses in ages 10–19, 10–15% in ages 20–49, and less than 5% over age 50 in both men and women. Patients are typically asymptomatic, but may report symptoms due to compression of mediastinal structures. When well-circumscribed, round/oval/saccular, and homogeneous lesions are present in the anterior mediastinum near the thymic bed, the possibility of thymic cyst should be considered. Although thymic cysts may measure water or fluid attenuation (between 0 and 20 Hounsfield Units) on CT (Figure 3C), they can manifest as higher density lesions. This feature is responsible for CT's inability to reliably distinguish cystic lesions from solid masses. In the case of suspected thymic cyst, MRI should be performed. Purely cystic lesions in the anterior mediastinum with no soft tissue nodules and no internal septations on MRI can reliably be diagnosed as unilocular thymic cysts.23Choi YW McAdams HP Jeon SC et al.Idiopathic multilocular thymic cyst: CT features with clinical and histopathologic correlation.AJR Am J Roentgenol. 2001; 177: 881-885Crossref PubMed Scopus (70) Google Scholar Cystic lesions that contain soft tissue components may represent mulitlocular thymic cysts or cystic thymoma. The diagnosis of cystic thymoma should be strongly considered in patients with a cystic anterior mediastinal lesion and symptoms related to myasthenia gravis or other paraneoplastic syndromes, especially men and women older than 40 years of age. A well-circumscribed lesion measuring water or fluid density with thin or imperceptible walls in one of the cardiophrenic angles can be confidently diagnosed as a pericardial cyst24Feigin DS Fenoglio JJ McAllister HA Madewell JE Pericardial cysts. A radiologic-pathologic correlation and review.Radiology. 1977; 125: 15-20Crossref PubMed Scopus (129) Google Scholar,25Jeung MY Gasser B Gangi A et al.Imaging of cystic masses of the mediastinum.Radiographics. 2002; 22 (Spec No): S79-S93Crossref PubMed Scopus (270) Google Scholar (Figure 3D). Normal thymic tissue is usually seen in young patients and should decrease in prominence with age. By age 40, the thymus should be replaced by fat. Thymic hyperplasia should be considered in young patients with uniform enlargement of the thymus compared with prior imaging, or in patients over the age of 40 with soft tissue in the thymic bed without focal mass or contour abnormality similar to normal thymus. In patients who have been treated with chemotherapy, radiation therapy, or corticosteroids, have been exposed to stresses such as burns or injuries, or who have known disorders such as myasthenia gravis, hyperthyroidism, collagen vascular diseases, or HIV, thymic hyperplasia should be considered when a low attenuation anterior mediastinal mass is identified. Although the most common manifestation of thymic hyperplasia is diffuse, symmetric enlargement of the thymus on CT, intralesional fat may be present and result in ill-defined regions of low attenuation (Figure 4A). In most patients, thymic hyperplasia can be diagnosed reliably when there is a typical CT appearance (e.g., enlarged but maintaining the shape of the thymus) in a patient following stress. However, sometimes the CT appearance is not straightforward and it may appear more nodular or bulky in configuration, resembling a thymoma or lymphoma. When the findings are not classic for thymic hyperplasia, one can either re-image after a sufficiently long period (∼3 months) to let the thymus decrease in size on its own or perform chemical shift MRI with in- and out-of-phase gradient echo sequences. Thymic hyperplasia and the normal thymus demonstrate loss of signal on out-of-phase images due to the suppression of microscopic fat interspersed between nonneoplastic thymic tissue, whereas thymic malignancies and lymphoma do not suppress on out-of-phase imaging26Inaoka T Takahashi K Mineta M et al.Thymic hyperplasia and thymus gland tumors: differentiation with chemical shift MR imaging.Radiology. 2007; 243: 869-876Crossref PubMed Scopus (159) Google Scholar,27Takahashi K Inaoka T Murakami N et al.Characterization of the normal and hyperplastic thymus on chemical-shift MR imaging.AJR Am J Roentgenol. 2003; 180: 1265-1269Crossref PubMed Scopus (60) Google Scholar (Figure 4B–D). With either confirmatory approach an unnecessary biopsy or surgery can be avoided. A homogeneous or slightly heterogeneous anterior mediastinal mass in men and women older than 40 years of age likely represents a thymoma28Benveniste MF Rosado-de-Christenson ML Sabloff BS Moran CA Swisher SG Marom EM Role of imaging in the diagnosis, staging, and treatment of thymoma.Radiographics. 2011; 31 (discussion 1861): 1847-1861Crossref PubMed Scopus (93) Google Scholar (Figure 5A). When this appearance is combined with symptoms of myasthenia gravis or other paraneoplastic syndrome (such as pure red cell aplasia/Diamond-Blackfan syndrome or hypogammaglobulinemia), there is little doubt about the diagnosis. As more than 80% of thymomas are accurately diagnosed on CT or MRI due to their typical cross-sectional appearance, tissue diagnosis is typically unnecessary.14Tomiyama N Honda O Tsubamoto M et al.Anterior mediastinal tumors: diagnostic accuracy of CT and MRI.Eur J Radiol. 2009; 69: 280-288Abstract Full Text Full Text PDF PubMed Scopus (146) Google Scholar Lymphadenopathy is typically absent, but pleural and/or pericardial spread may be identified in advanced (stage IV) disease and is often quite pathognomonic for thymic malignancy. In the setting of a large anterior mediastinal mass with features such as heterogeneity, local invasion, lymphadenopathy, and pleural effusion, thymic epithelial neoplasms other than thymoma such as thymic carcinoma (Figure 5B) and carcinoid should be considered.29Rosado-de-Christenson ML Strollo DC Marom EM Imaging of thymic epithelial neoplasms.Hematol Oncol Clin North Am. 2008; 22: 409-431Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar On 18F-FDG PET/CT, thymic carcinomas and carcinoids typically demonstrate greater FDG uptake than thymomas.30Endo M Nakagawa K Ohde Y et al.Utility of 18FDG-PET for differentiating the grade of malignancy in thymic epithelial tumors.Lung Cancer. 2008; 61: 350-355Abstract Full Text Full Text PDF PubMed Scopus (84) Google Scholar,31Inoue A Tomiyama N Tatsumi M et al.(18)F-FDG PET for the evaluation of thymic epithelial tumors: Correlation with the World Health Organization classification in addition to dual-time-point imaging.Eur J Nucl Med Mol Imaging. 2009; 36: 1219-1225Crossref PubMed Scopus (37) Google Scholar In patients with enlarged lymph nodes or lobulated soft tissue masses in the mediastinum on cross-sectional imaging, which may or may not be seen in association with lymphadenopathy in the lower neck or axilla, a lymphoma such as Hodgkin disease and mediastinal large cell non-Hodgkin lymphoma should be considered. Although it may be difficult to distinguish lymphoma from other soft tissue lesions in the mediastinum, the infiltrative nature of so
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