|Year : 2015 | Volume
| Issue : 4 | Page : 1033
Ectopic thymoma presenting as a large intrathoracic mass
Sunita Dashottar1, AK Singh1, Virender Suhag2, BS Sunita3
1 Department of Radiodiagnosis and Imaging, Command Hospital (EC), Kolkata, West Bengal, India
2 Department of Radiation Oncology, Command Hospital (CC), Lucknow, Uttar Pradesh, India
3 Department of Pathology, Command Hospital (CC), Lucknow, Uttar Pradesh, India
|Date of Web Publication||15-Feb-2016|
A K Singh
Department of Radiodiagnosis, Command Hospital (EC), Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
Thymoma is an epithelial neoplasm of the thymus, which commonly lies in the anterior mediastinum. Unusually it can be found in other locations as well. Ectopic thymoma rarely presents as an intrathoracic tumor. We report a case of an ectopic thymoma presenting as a giant right intrathoracic tumor that was treated with resection. The patient was a 49-year-old postmenopausal lady who presented with heaviness in chest and breathlessness. Detailed investigation including chest computed tomography scan and magnetic resonance imaging revealed a well-defined large solid tumor in the right thoracic cavity. Surgery was performed based on the radiological findings. A large solid tumor measuring 12 cm ΄ 10 cm ΄ 8 cm was found in the thoracic cavity, adherent to the pericardium, diaphragm and the right mediastinal pleura without apparent invasion. The tumor was completely resected. The diagnosis given as World Health Organization classification-Type B1 Muller-Hermelink classification-predominantly cortical thymoma.
Keywords: Ectopic thymoma, intrathoracic mass, magnetic resonance imaging
|How to cite this article:|
Dashottar S, Singh A K, Suhag V, Sunita B S. Ectopic thymoma presenting as a large intrathoracic mass. J Can Res Ther 2015;11:1033
| > Introduction|| |
Masses in the anterior mediastinum can be neoplasms (e.g. thymomas, thymic carcinomas, or lung metastases) or nonneoplastic conditions (e.g. intrathoracic goiter). Thymomas are tumors developing mainly in the thymus, are located in the anterior mediastinum, with 96% of the tumors occurring in the anterior or anterosuperior mediastinum, and only 4% being ectopic tumors. , Ectopic thymomas have been described in the neck, middle mediastinum, posterior mediastinum, lung, and pleura, few reports have described giant intrathoracic tumors. Although thymomas can spread locally, they are much less invasive than thymic carcinomas. Patients with thymomas have 5 years survival rates of approximately 78%. However, 5 years survival rates for thymic carcinomas are only approximately 40%.  We report, herein, a giant intrathoracic tumor that was discovered during a clinical workup to determine the cause of heaviness in the chest associated with breathlessness in a patient.
| > Case report|| |
This 49-year the-old postmenopausal lady had presented in the emergency department with acute onset breathlessness and heaviness in the chest. She was an old case of bronchial asthma and gave a history of a similar episode associated with fever with chills and rigors 2 months back.
Clinically, there was no pallor, peripheral adenopathy, clubbing or edema. Chest auscultation revealed reduced breath sounds in right lower zone. Other systemic examination was unremarkable. Her hemogram and biochemical parameters didn't reveal any significant abnormality. Radiograph of the chest [Figure 1] showed 12 cm × 10 cm × 7.6 cm well-defined homogenous soft tissue mass lesion in the right hemithorax extending from the hilum to the level of hemi-diaphragm. The medial border merged with the mediastinum with loss of the cardiac silhouette and laterally the mass was abutting the chest wall. There was no air bronchogram, calcification, cavitation or rib destruction.
|Figure 1: Radiograph of the chest posteroanterior view showing a well-defined homogenous soft tissue density mass in the right lower hemithorax silhouetting the heart and the diaphragm|
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Computed tomography (CT) scan chest [Figure 2] showed a large 11.3 (AP) × 6.5 (CC) × 7.1 (TR) well-defined enhancing solid mass in the right para cardiac region extending from the level of hilum to the diaphragm. Anteriorly it was extending up to anterior chest wall with loss of intervening fat plane. However, there was no infiltration of chest wall or ribs noted. Medially it was closely abutting the pericardium in the superior aspect. Inferiorly the mass lesion was abutting the right hemidiaphragm. Two pretracheal lymph nodes were seen, largest lymph node measuring 13 mm × 9 mm.
|Figure 2: Contrast-enhanced computed tomography chest showing a homogenously enhancing soft tissue attenuating mass with focal calcification at the periphery in right hemithorax|
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Magnetic resonance imaging (MRI) thorax [Figure 3] showed 11.8 cm × 9.9 cm × 7.6 cm well-defined solid mass lesion in the right hemithorax closely abutting the mediastinum extending from the hilum to the hemi-diaphragm. The mass was compressing and displacing the right pulmonary artery and pulmonary vein superiorly. Medially it was closely abutting the pericardium. Laterally it was extending up to the lateral chest wall. Inferiorly it was indenting the superior surface of the VIII segment of the liver. Anteriorly it was closely abutting the anterior chest wall. The imaging findings suggested the tumorous lesion not invading the chest wall, but to have some adhesion to the diaphragm and pleura.
|Figure 3: Magnetic resonance imaging of the chest showing soft tissue signal intensity mass closely abutting the pericardium|
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As the patient was worsening symptomatically in view of breathlessness and heaviness in chest; and the MRI findings were characteristic of thymoma, no biopsy was attempted and the patient was upfront taken up for resection by median sternotomy approach. It was considered that percutaneous needle biopsy would yield a definitive diagnosis, but this procedure was not performed considering the risk of tumor cell dissemination and bleeding from the tumor. Peroperatively, a large well-encapsulated solid mass was found adhered to but not frankly invading the pericardium and the surrounding lung parenchyma. The mass was successfully excised without much difficulty [Figure 4] and [Figure 5]. The histopathology [Figure 6] and [Figure 7] showed prominently lobulated tumor separated by fibrous trabeculation. It comprised predominantly of lymphoid cells and scanty neoplastic thymic cells having oval shape with no nuclear atypia. Epithelial cells were faintly made out by their pale staining nature. The diagnosis given as World Health Organization (WHO) classification-Type B1 Muller-Hermelink classification-predominantly cortical thymoma. As the tumor was grossly adherent to surrounding fatty tissues without invasion of neighboring organs, it was classified Masaoka stage IIB. Her postop recovery was uneventful, and she is doing well after 1 year of follow-up.
|Figure 6: Photomicrograph of histopathological examination (low power ×10 view)|
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|Figure 7: Histopathological examination of the mass (high power ×20 view) showing prominently lobulated tumor separated by fibrous trabeculation comprising predominantly of lymphoid cells and scanty neoplastic thymic cells having oval shape with no nuclear atypia. Epithelial cells are faintly made out by their pale staining nature|
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| > Discussion|| |
The thymus gland is located behind the sternum in front of the great vessels; it reaches its maximum weight at puberty and undergoes involution thereafter. Thymoma, the most common neoplasm of the anterior mediastinum, originates within the epithelial cells of the thymus. ,, It accounts for 20-25% of all mediastinal tumors and 50% of anterior mediastinal masses. Embryologically, thymic epithelium arises bilaterally from the third and probably fourth bronchial pouches and migrates into the anterosuperior mediastinum. Ectopic occurrence of thymoma results from the failure of this migration. Most patients are between 40 and 60 years of age. There is slight male predominance. Of patients with a thymoma, one-third to one-half are asymptomatic. One-third of cases are found incidentally on radiographic examinations during a workup for myasthenia gravis (MG). ,,
Although thymomas can present as huge masses, the symptoms and stage may not always correlate with tumor size.  A large tumor size is a significantly poor prognostic factor of thymomas. Limmer et al.  reviewed previously reported giant thymomas. According to the article, all of the giant tumors were Type A, AB and B1 according to the WHO classification. Interestingly, although a large tumor size is a poor prognostic factor, the resected giant thymomas tended to be low-grade thymomas.
Patient may present with local symptoms related to the tumor encroaching on surrounding structures like cough, chest pain, superior vena cava syndrome, dysphagia, and hoarseness of voice. 30-40% of patients with thymoma experience symptoms of MG. An additional 5% of patients have other systemic syndromes including red cell aplasia, dermatomyositis, systemic lupus erythematous, Cushing syndrome and syndrome of inappropriate antidiuretic hormone secretion.
Posteroanterior (PA) and lateral chest radiographs can detect most thymomas. On the PA view, the lesion typically appears as a smooth mass in the upper half of the chest. The mass usually projects predominantly into one of the hemi thoraces. On CT scan, thymoma usually appears as a well-defined round or oval mass located anterior to the great vessels and heart, below the left innominate vein. Features suspicious for malignancy include vascular invasion, encasement, and pleural dissemination positron emission tomography scan helps in staging and in excluding extra mediastinal involvement. 
Definitive diagnosis is needed before surgical removal of a thymoma is planned. In cases of large but potentially resectable intrathoracic lesions, a preoperative histological diagnosis is established through the least possible invasive procedure. Transthoracic CT-guided tru-cut biopsy is effective in differentiating thymomas from lymphomas, sarcomas, chest wall tumors, solitary fibrous tumors and metastatic tumors. Hemorrhagic shock induced by spontaneous rupture of a giant thymoma has been reported, and caution is warranted when considering biopsy.  There is a continuum of differentiation from thymoma to thymic carcinoma. Carcinoma and thymoma can exist synchronously. Heterogeneity is common within thymomas and cellular composition correlates with biological behavior of the tumor. ,,
As the only curative treatment, surgery remains the baseline attempt in thymoma therapy. Complete or partial median sternotomy with a complete thymectomy is the operative approach of choice. In advanced tumors, especially if the lung or pleural space is invaded, the extension of a sternotomy to a hemi-clamshell incision or a full clamshell incision can be suitable. Approaches like transcervical and video-assisted thoracoscopic thymectomy for thymoma may be considered for noninvasive thymomas if performed carefully in experienced hands, though minimally invasive approach for the resection of thymomas is not currently recommended.  Our patient was managed successfully by surgical resection. Radiotherapy is an important component of the multimodality approach to thymic neoplasms. For patients with unresectable disease, a dose of 60-70 Gy is recommended, whereas adjuvant radiotherapy doses range from 45 to 50 Gy for clear or close margins, 54 Gy for R1 margins, and 60 Gy or greater for R2 margins, 1.8-2.0 Gy per daily fraction. Patients with unresectable or recurrent thymic neoplasms are considered candidates for systemic chemotherapy. Patients who present with locally advanced disease can be restaged after treatment with chemotherapy to either undergo surgery or to consider further radiotherapy and chemotherapy if they did not respond adequately. In the era of targeted therapy, there have been investigations into specific targets in thymic neoplasms that may improve response to therapy. 
| > Conclusion|| |
Ectopic thymoma, even if as a very rare occurrence, should always be included in the differential diagnosis whenever a large intrathoracic mass is observed.
| > References|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]