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REVIEW ARTICLE
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Rare mediastinal masses – imaging review


1 Department of Radiology, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
2 Department of CT Surgery, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India
3 Department of Pathology, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India

Date of Submission11-Aug-2019
Date of Acceptance30-Dec-2019
Date of Web Publication03-Oct-2020

Correspondence Address:
Sujata Patnaik,
Department of Radiology, Nizam's Institute of Medical Sciences, Punjaguta, Hyderabad - 500 082, Telangana
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.JCRT_587_19

 > Abstract 


Mediastinal masses span a wide histopathological and radiological spectrum. Apart from primary thymic/thyroid masses and lymphomas, all other mediastinal masses can be considered rare tumors. Chest radiography and Computed tomography (CT) are helpful to characterize the mass and can reach a diagnosis or a close differential diagnosis. MRI in special situations can depict the pericardial/vascular invasion better, and diffusion studies can recognize benign from the malignant mass. The imaging details of 15 histopathologically proven cases of rare mediastinal tumors are described. Neuroblastoma (NB) (n = 3) was the most common among the rare masses. Three were sarcomas, one liposarcoma, one synovial sarcoma, one spindle-cell tumor and one Hemangiopericytoma (HPC). Lymphoma presenting as a single mass, neuroendocrine tumor (NET) of the anterior mediastinum, paraganglioma of the posterior mediastinum (one each) were seen. The imaging features of these rare mediastinal masses have to be kept in mind for appropriate diagnosis.

Keywords: Rare tumors, mediastinum, neuroblastoma



How to cite this URL:
Patnaik S, Malempati AR, Uppin M, Susarla R. Rare mediastinal masses – imaging review. J Can Res Ther [Epub ahead of print] [cited 2020 Oct 28]. Available from: https://www.cancerjournal.net/preprintarticle.asp?id=297202




 > Introduction Top


Mediastinal masses span a wide histopathological and radiological spectrum. Apart from primary thymic/thyroid masses and lymphomas, all other mediastinal masses can be considered rare tumors. Chest radiography is the initial routine investigation. It can distinguish mediastinal from the pulmonary masses. Computed tomography (CT) is done to characterize the mass and can reach a diagnosis or a close differential diagnosis. Magnetic resonance imaging (MRI) in special situations can depict the pericardial/vascular invasion better, and diffusion studies can recognize benign from the malignant mass. We studied the spectrum of imaging features in rare mediastinal masses and assessed the role of CT scan in their diagnosis and evaluation. The imaging details of 15 histopathologically proven cases of rare mediastinal tumors were studied. Out of 15, two were female; maximum was in the age group of <10 years (n = 4), the youngest was 4 years, and the oldest was 58 years. Neuroblastoma (NB) (n = 3) was the most common among the rare masses. Three were sarcomas, one liposarcoma, one synovial sarcoma, and one spindle-cell tumor. Hemangiopericytoma (HPC), a very rare tumor, was observed. Lymphoma presenting as a single mass, neuroendocrine tumor (NET) of the anterior mediastinum, paraganglioma of the posterior mediastinum were one each in our observation. Fibrosing mediastinitis (FM) presenting as highly vascular mass was one. There was one case of the inflammatory myofibroblastic tumor (IMT) which was mimicking angiosarcoma of cardiac origin. A few cases of bronchogenic cyst, parathyroid adenoma, and Castleman's disease were benign tumors we encountered.


 > Cystic Masses Top


Cystic masses represent 15%–20% of mediastinal masses.[1] A smooth oval mass with homogenous attenuation with no enhancement and no infiltration are usual findings of benign cysts in CT. Any cysts may have higher attenuation may be due to calcific, proteinaceous, mucous, or hemorrhagic component.


 > Bronchogenic Cysts Top


Bronchogenic cysts arise from the ventral budding of the tracheobronchial tree commonly located at the tracheobronchial tree in 52% and paratracheal in 19%.[2] They are lined by the respiratory epithelium and their capsule contains cartilage, smooth muscle, and mucous gland tissue.[3] Infection and hemorrhages are common complications presenting as a sudden increase in size. In chest X-ray (CXR), the cyst appears as well-defined solitary opacity anterior to the carina bulging into the right hilum. On CT, the mass is smooth round with imperceptible wall and uniform attenuation [Figure 1]. The attenuation value maybe of water or soft tissue. The value may be more than 100, due to proteinaceous content. The air within the cyst indicates a secondary infection of communication with the bronchial tree. Calcification may occur within a wall or within cyst content. On T2W images, the fluid has high-signal intensity; on T1, the fluid has a variable signal due to protein, hemorrhage, and mucoid material.
Figure 1: 35F bronchogenic cyst: Well-defined smoothly marginated hypodense mass appearing as the left superior mediastinal mass. On computed tomography, the space-occupying lesion is nonenhancing hypodense homogeneous in attenuation

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 > Other Cystic Masses Top


Thymic cysts represent 1% of mediastinal masses.[4] These cysts derive from the thyropharyngeal duct. They can be seen along the embryonic thymic gland from the angle of the mandible to the mediastinum. Congenital cysts are unilocular, whereas acquired one are multilocular, and they are associated with inflammation or an inflammatory neoplasm such as Hodgkin's lymphoma, thymic tumor, and germ-cell tumor. Approximately 50% of thymic cysts are detected incidentally in the first two decades of life. On CT, the congenital cysts are well-defined with water attenuation and imperceptible wall [Figure 2]. On T1, hypointense, and on T2W, the mass is high signal. Sometimes, the cyst may show a variable signal due to protein, hemorrhage, and mucoid material. Fluid-fluid level may be observed. Acquired cysts are multilocular, contain turbid fluid, and have a thick, fibrous wall. Histo-pathological examination (HPE) reveals inflammation.
Figure 2: 60M thymic cyst: Well-defined smooth-walled opacity on the right side with vascular opacities seen through it indicating mediastinal mass with positive hilum overlay sign in the topogram. Axial plain and contrast study shows water density space-occupying lesion with an imperceptible wall with no enhancement

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Duplication cyst, neurenteric cyst, pericardial cysts, lymphangioma, and pancreatic pseudocysts are other cystic lesions of the mediastinum. Esophageal duplication cysts are developmental in origin and classified as a foregut cyst that is either bronchogenic or neuroenteric.[5] Esophageal duplication cysts are uncommon and are asymptomatic. Dysphagia and pain are the symptoms due to compression on neighboring structures, when it is located adjacent to or within the wall. Ectopic gastric mucosa in the cyst may cause hemorrhage or perforation of the cyst or infection. On CT/MRI, the lesion looks similar to the bronchogenic cyst except for thickened walls and more intimate contact with the esophagus [Figure 3]. Barium study shows extrinsic/intraluminal compression due to close contact with esophagus. Radionuclide scan with Tc-99 m sodium pertechnetate may be helpful in pediatric patients. In 50% of duplication cysts contain ectopic gastric mucosa.
Figure 3: 54M esophageal duplication cyst: Axial plain and contrast scan delineates the nonenhancing cystic lesion along the esophagus. The patient presented with chest pain and cough due to compression over the adjacent structures

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 > Castlemans Disease Top


It is a lymphoproliferative disorder and not true cancer. There can be lymphnodal masses and may mimic lymphoma. The common sites of involvement include the mediastinum, hila, cervical, and mesentery retroperitoneum. On CT, the lymphoid mass is sharply outlined and is of muscle density. Spotty coarse central calcifications may be seen. Enhancing rim represents the vascular capsule. Increased enhancement is seen in hyaline vascular type and slight enhancement in the plasma cell type.


 > Parathyroid Adenoma Top


The embryological origin of parathyroid glands is the endoderm of the 3rd and 4th pharyngeal pouch. It is well-known that the parathyroid gland may be found in aberrant location mainly in thyroid parenchyma or in the mediastinum.[6] It is difficult to locate ectopic parathyroid adenoma. Hence, difficult to diagnose, and hence, there is a delay in the treatment. Eighty-eight percent of hyperparathyroidism is by parathyroid adenoma. Ultrasonography and four-dimensional (4D) CT are commonly used to diagnose parathyroid adenoma. Galvin et al. highlighted the fact that the smallest lesion detected by scintigraphy was 10 mm versus 4 mm in 4D CT. The pattern of contrast enhancement is characteristic.[7] It shows intense enhancement in the arterial phase with peak enhancement between 25 and 60 s following contrast injection and wash out in the delayed phase. There is “salt and pepper” appearance on MRI. This differentiates it from its mimics like lymph node [Figure 4].[8]
Figure 4: 45M parathyroid adenoma presenting with features of hyperparathyroidism showing enhancing anterior mediastinal mass

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 > Hemangiopericytoma Top


HPC accounts for 1% of all vascular tumors and is very rare and only few reported cases in literature. Tumor is large, highly vascularized, and highly infiltrative occurs commonly in the skin, subcutaneous soft tissue, muscles of extremities retroperitoneum, but rarely in the lung, trachea, and mediastinum potentially malignant tumor arising from the pericytes of blood vessel.[9] Intrapulmonary HPC is more common as compared to the mediastinal one. Tumors are composed of closely packed spindle cells and prominent vascular channels. Histopathologically differentials are solitary fibrous tumors and synovial sarcoma. Usually, these tumors are discovered incidentally as noncalcified mass on CXR with no specific radiological, clinical features. On CT, the mass is of soft-issue attenuation. High vascularization is expected on imaging as in our case [Figure 5].[10] Here, the mass is heterogeneous with heterogeneous enhancement with foci of calcification and mass effect. On MRI, mass is intermediate signal on T1W and high signal on T2W images. Triple sign bright, dark, gray signal because of tumoral bleed may be observed.
Figure 5: 6 M HPE proven hemangiopericytoma: Large soft-tissue dense heterogeneously enhancing mass in the mediastinum with calcification and necrosis infiltrating the aorta, superior vena cava, and pulmonary artery

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 > Neurogenic Tumors Top


Nerve sheath tumors are common in this location accounts for 70%. Sympathetic ganglion tumors are 20%.[11] Ganglioneuroma comprises 25% of neurogenic tumor of mediastinal neurogenic tumor arising from the neuronal cells of sympathetic ganglion.[12] Radiologically, the tumors are well marginated occurring along the anterolateral aspect of spine spanning 3–5 vertebrae [Figure 6]. Whorled appearance is due to curvilinear bands of low-signal intensity that reflects collagenous fibrous tissue in the mass in T2W images. They show heterogeneous enhancement on contrast administration. Ganglioneuroblastoma is the least common type of neurogenic tumor and shows intermediate cellular maturity between ganglioneuroma and NB.
Figure 6: Case of ganglioneuroma of the posterior mediastinum in a 34-year-old male: Chest radiographs reveal positive cervicothoracic sign in preoperative film and postoperative chest X-ray reveals total excision of a mass

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Primary mediastinal NB accounts for 14% of all NBs. For NB, a common location is the posterior mediastinum arising from the paravertebral sympathetic chain. CXR demonstrates homogeneous opacity. If tumor is large, it causes extrinsic compression and displacement of the trachea and small bronchus. Erosion of posterior ends of ribs and asymmetric widening of intercostal spaces were noted. Intraspinal extent is seen as the loss of vertebral height and widening of neural foramina on the lateral radiograph. Approximately 50% of the lesion show calcification on radiograph.[13] CT confirms the presence of tumor and helps to define the location and extent of mass/adjacent organ involvement/vascular invasion [Figure 7]. Calcification is better delineated on CT and seen in 90% of cases. Highly aggressive tumor, heterogeneous, nonencapsulated space-occupying lesion with hemorrhage, necrosis, calcification, cystic degeneration as in this case [Figure 8]. MRI is done for the assessment of extradural intraspinal extent of tumor. Forty-eight percent of NBs have metastatic disease at presentation.[14] The common sites include 70% in bone marrow and 55% in bone.[15] We had a patient presented with distant lymph nodal and skull metastasis [Figure 9].
Figure 7: 2 M a case of neuroblastoma: Highly aggressive tumor heterogeneous, nonencapsulated with hemorrhage, necrosis, calcification, cystic degeneration with infiltrating aorta and pericardium

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Figure 8: 4F case of neuroblastoma: Chest X-ray and plain contrast enhanced computed tomography scan reveals a posterior mediastinal mass having calcifications

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Figure 9: 4F metastatic neuroblastoma: Chest X-ray and computed tomography of the abdomen and brain. Primary mass is seen in the posterior mediastinum extending along the chest wall, abdominal retroperitoneal, pelvic adenopathy, as shown in axial contrast-enhanced computed tomography abdomen and right frontal calvarial metastasis. Note the bony metastasis is associated with large-enhancing extradural soft tissue

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Paraganglioma arises from neuroectodermal cells associated with the ganglion cell of autonomic nervous system. It is discovered incidentally in 50% of cases, and the rest may be symptomatic. The common sites are aortopulmonary (aortic arch) and aortic sympathetic (postmediastinum) regions. It is quite rare and accounts for 0.3% in a large series of over 1000 mediastinal masses.[16] No age or sex predilection is seen. CXR is nonspecific. CT may be extremely valuable demonstrating the soft-tissue mass in a characteristic location. The dynamic scan shows extreme vascular mass [Figure 10]. Differential diagnosis of highly vascular mass in the mediastinum includes Castleman's disease, hemangioma, and mediastinal goiter.
Figure 10: 45M paraganglioma: Topogram and contrast-enhanced axial image reveals intense in homogenously enhancing space-occupying lesion in the posterior mediastinum eroding adjacent vertebra. The aorta is compressed and displaced laterally

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 > Fibrosing Mediastinitis Top


FM is also known as mediastinal fibrosis/sclerosing mediastinitis. It is a benign uncommon progressive condition characterized by invasive proliferation of fibrous tissue in the mediastinum. FM presents with compression over the tracheobronchial tree, pulmonary artery/vein, superior vena cava, and esophagus [Figure 11]. FM is of two subtypes: granulomatous [Figure 12] and nongranulomatous [Figure 11]. Tuberculosis and histoplasmosis are common granulomatous FM. The nongranulomatous is idiopathic reaction to autoimmune syndrome, drugs, and radiation. This disease is frequently associated with retroperitoneal fibrosis, primary sclerosing cholangitis, and orbital pseudotumor.[17] They mimic malignancy and present as mediastinal or hilar mass. It may be focal in 80% and diffuse in 20%. The age of presentation is 13–65 years with female predominance.
Figure 11: 25F case of fibrosing mediastinitis: Plain and contrast-enhanced scan reveals a soft-tissue dense-enhancing mass in the mediastinum infiltrating and compressing the vasculature, bronchi, as shown in the first three images. Reconstructed image shows the extent of the space-occupying lesion

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Figure 12: 35M case of fibrosing mediastinitis, granulomatous: There is enhancing soft-tissue dense mass with calcification and encasing superior vena cava (SVC) narrowing its lumen, encasing pulmonary artery, compressing trachea, and bronchi. Note: Esophageal diverticulum on the right side in all images

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CXR shows mediastinal widening, enlarged nodes in hila, paratracheal region, and subcarinal area. The narrowing of bronchi and calcifications in nodes may be appreciated. The presence of calcification indicates granulomatous etiology, as shown in [Figure 12].[18] Contrast-enhanced CT is diagnostic, and the extent and severity can be well delineated. The length and degree of stenosis are well assed in multiplanar reconstructions. CT angiogram is helpful to note vascular involvement.

Radiologically, FM is of two types, namely focal and diffuse variety. Focal is more common in granulomatous variety presenting as a focal mass of soft-tissue attenuation. Calcifications in nodes are the common finding. Diffuse variety involves multiple compartments and compresses the trachea, esophagus, and mediastinal vascular structures. This is commonly seen in idiopathic or nongranulomatous variety. Postcontrast, the lesions show variable enhancement.[19] MRI is better for vascular involvement, but the detection of calcification is difficult. On T1W images, a mass is intermediate signal, and on T2W, it is a variable signal. Areas of T1 and T2 hypointensity represent calcification and fibrosis. T2 hyperintensity represents inflammatory tissue. 18F-fluorodeoxyglucose positron emission tomography show tracer uptake in active inflammatory areas.


 > Inflammatory Myofibroblastic Tumors Top


IMT is one of the rarest groups of neoplasm composed of a mixture of spindle-shaped myofibroblast, variable amount inflammatory cell (eosinophil, plasma cell, and lymphocytes).[20] Other names include plasma cell granuloma and inflammatory myofibroblastic proliferation/fibroxanthoma/xanthogranuloma. Most frequent organs involved are lungs and the orbits. There are different etiologies such as chronic infections, autoimmune disease, and trauma; Ig G 4 disease which may be associated. Histological studies are critical to properly diagnose them. Immunohistochemical study of T- and B-cell subpopulation, CD34, CD117, S-100, and C-Kit may be helpful in distinguishing IMT from other soft-tissue tumors. Positive immunochemical staining of anaplastic lymphoma kinase (ALK) is in approximately 40%–100% of IMTs, depend on anatomical structures they arise. This finding suggests a possible neoplastic cause of IMTs. ALK expression could be a prognostic factor of aggressiveness for IMT. Five percent of IMT may be metastatic.[21]

Although extremely rare, we had a case of IMT misdiagnosed as densely enhancing infiltrative cardiac mass [Figure 13]. Radiologically, the IMTs are solitary, well-defined, peripherally situated lung mass with predominance of lower lobes.[22] On CT, the mass shows heterogeneous enhancement. Fifteen percent show calcifications. Lesions invade adjacent structures. Treatment is surgery to exclude malignancy. Spontaneous regression may occur, and local expansion may cause significant morbidity. Radiotherapy, chemotherapy, and corticosteroid treatment are treatment modalities.
Figure 13: 13F inflammatory myofibroblastic tumors: Contrast-enhanced computed tomography reveals large infiltrating enhancing mass in the mediastinum extending into the left atrium as shown in contrast-enhanced computed tomography and echocardiogram

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 > Sarcomas Top


Sarcomas are rare and account for <2% of all soft-tissue tumors. Soft-tissue sarcoma commonly seen in extremities, and primary mediastinal is rare and accounts for <10% of mediastinal tumors.[23] These tumors are classified as pleomorphic, biphasic, and monophasic spindle-cell tumor. Important pleomorphic tumors are MFH, liposarcoma, malignant mesothelioma, and thymic carcinosarcoma. Monophasic spindle cell tumors are synovial sarcoma, sarcomatous/spindle cell carcinoma, solitary fibrous tumor, malignant peripheral nerve sheath tumor, and fibrosarcoma.[24] The subtypes include liposarcoma, synovial sarcoma, unspecified sarcoma/spindle cell sarcoma, leiomyosarcoma, embryonal rhabdomyosarcoma, Ewings family angiosarcoma, and undifferentiated pleomorphic sarcoma. Survival is favorable in liposarcoma and unfavorable in pleomorphic sarcoma and angiosarcoma. These tumors are large, ill-defined, and heterogeneous with infiltrating margins. Findings are nonspecific to subtype. The common age of presentation is 35–58 years, with a male-to-female ratio of 1.6:2 [Figure 14].[25]
Figure 14: 22M Spindle cell tumor: Infiltrating soft-tissue mass on the left lateral aspect of the mediastinum

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Liposarcoma frequently occurs in the posterior mediastinum. Liposarcoma is symptomatic at the time of presentation in contrast to lipoma. The tumor is inhomogeneous in the CT scan, and MRI differentiates liposarcoma from lipoma [Figure 15]. Synovial sarcoma has been defined by the WHO in 2002 as a type of mesenchymal tissue cell tumor that exhibits epithelial differentiation and represents the 3rd most common soft-tissue sarcoma in adults accounting for 10%. It is prevalent in adolescents and young adults (15–40 years). Although 85% of synovial sarcomas arise in the joints of lower limb, they occur rarely in mediastinum. Radiological features are nonspecific. Multidetector CT mediastinal synovial sarcoma appears as well-defined heterogeneously enhancing mass-containing areas of fluid density representing hemorrhage and necrosis [Figure 16] and [Figure 17]. Calcification is uncommon in contrast to lower limb synovial sarcoma. Lymphadenopathy is rare. Often, the exact site of origin from pleura/mediastinum/lung is unclear [Figure 18]. On MRI, the space-occupying lesion shows less vascularity and triple sign pattern on T2W images consisting of bright, dark, gray areas representing tumor, hemorrhage, necrosis, respectively. These are very aggressive tumor with a high recurrence rate. Invasion to adjacent structures and hematogenous spread can occur. Lymphatic spread is uncommon. Overall, 5-year survival is 50%, and poor prognostic factors include age older than 20 years, female sex, incomplete resection, tumor size >5 cm, extensive tumor necrosis, a high number of mitosis >10/10 high-power fields, and neurovascular invasion.
Figure 15: Liposarcoma having solid and lipomatous component compressing mediastinal vasculature in 27 M

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Figure 16: 38M Synovial sarcoma of the mediastinum: large heterogeneously enhancing mass infiltrating aorta, pericardium, pleura

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Figure 17: Another case of synovial sarcoma in a 40-year-old male. Heterogeneous mass with no evidence of calcifications

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Figure 18: 31M with aggressive synovial sarcoma-occupying entire right hemithorax with infiltration into adjacent structures and gross mass effect

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 > Primary Neuroendocrine Tumors Top


Primary NET of the mediastinum is very rare. Its origin is unclear and may arise from thymic proper or paraganglionic structures within the mediastinum or may result from neoplastic transformation in misplaced embryonal rests within the mediastinum. Most of NETs mediastinum is of thymic origin and very rarely from the mediastinum. Unlike carcinoid from Gastro-intestinal tract (GIT)/Lung, these tumors are highly aggressive and found to be malignant in 82% as opposed to bronchial carcinoid 26%.[26] It is common in the age group of 40–50 years.[27] Clinically, they may be asymptomatic or present with compression of adjacent mediastinal structures, with endocrinopathy or with symptoms due to metastatic disease. Radiologically present as ill-defined lobulated homogenously moderately enhancing mass in the anterior mediastinum. Infiltration to adjacent vascular structures is common. Punctate calcification and necrosis may be observed. Lymphadenopathy, metastasis to liver, lung, pancreas, pleura, and bone are common. The prognosis is very poor. The case we encountered was a 58-year-old male presented with Shortness of breath (SOB). It was infiltrating all the arch vessels in the form of complete encasement [Figure 19].
Figure 19: 58M neuroendocrine tumor of the mediastinum: Contrast-enhanced axial images in mediastinal window reveals enhancing soft-tissue mass in the anterior mediastinum infiltrating arch vessels. Lungs are clear as evidenced in coronal reconstructed image in the lung window

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 > Conclusion Top


The imaging features of rare mediastinal masses have to be kept in mind for appropriate evaluation. Thymic and thyroid masses and lymphomas are the most common. NB and paraganglioma are not uncommon. Sarcoma, HPC, NET FM, and IMTs though rare may be encountered in practice. Hence, one should be familiar with these entities.

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Conflicts of interest

There are no conflicts of interest.



 
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