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Thymoma Workup

  • Author: Kendrix J Evans, MD, MS; Chief Editor: John Geibel, MD, DSc, MSc, MA  more...
 
Updated: Dec 16, 2015
 

Laboratory Studies

The diagnosis of a thymoma usually is clinically based on radiologic findings. Laboratory studies generally are not indicated.

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Imaging Studies

Radiography

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, overlying the superior portion of the cardiac shadow near the junction of the heart and great vessels.

The mass usually projects predominantly into one of the hemithoraces. On the right, the silhouette sign is present and the ascending portion of the aortic arch is obliterated. Conversely, if the thymoma is on the left, the silhouette sign is obscured and the aortic knob is identified behind the mass.

Computed tomography

Computed tomography (CT) may delineate a mass further or may detect a smaller tumor that was missed by radiography (see the image below). Chest CT is the imaging procedure of choice in patients with myasthenia gravis (MG). Thymic enlargement should be determined because most enlarged thymus glands visualized on CT represent thymomas.

CT scan clearly illustrates mass in right anterola CT scan clearly illustrates mass in right anterolateral mediastinum.

CT with intravenous contrast dye is preferred to show the relations between the thymoma and surrounding vascular structures, to define the degree of its vascularity, and to guide the surgeon in removal of a large tumor, possibly involving other mediastinal structures.

Positron emission tomography

A case report found positron emission tomography (PET) to be invaluable in confirming the diagnosis of an invasive malignant thymoma.[5] Although CT revealed evidence of an anterior mediastinal mass, PET showed a hypermetabolic mass consistent with this location, thereby raising suspicion of malignancy. Subsequent resection of the mass revealed a minimally invasive thymoma due to capsular invasion. PET should be added to the armamentarium as an available diagnostic modality to aid in staging and excluding extramediastinal involvement.[5]

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Fine-Needle Aspiration and Biopsy

If a patient presents with atypical features or is found to have an invasive tumor and is under consideration for induction therapy, a preoperative biopsy is indicated. The limited anterior mediastinotomy (Chamberlain approach) is the standard approach that typically is performed over the projection of the tumor. A thoracoscopic approach for biopsy also can be used.

Controversy exists over the efficacy of fine-needle aspiration (FNA). FNA has been reported by some to be beneficial in making the diagnosis of a thymoma. Performing a core biopsy in conjunction with FNA is a modality that can increase the accuracy with which thymomas can be differentiated from other neoplasms, such as lymphomas and germ cell tumors.

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Histologic Findings

Traditionally, thymomas have been classified into three histologic types according to the cell type that is predominant—lymphocytic, epithelial, or lymphoepithelial. A pathologic classification was developed by the World Health Organization (WHO). In a study conducted in Japan between 1973 and 2001 of a series of 100 resected thymomas, prognostic categories were distinguished by using this WHO classification (see Table 2 below).[6]

Table 2. World Health Organization (WHO) Pathologic Classification and Associated Prognostic Categories (Open Table in a new window)

Type Histologic Description Disease-Free Survival at 10 years,* %
A Medullary thymoma 100
AB Mixed thymoma 100
B1 Predominantly cortical thymoma 83
B2 Cortical thymoma 83
B3 Well-differentiated thymic carcinoma 35
C Thymic carcinoma 28
*Series of 100 thymomas resected in Japan between 1973 and 2001 using WHO classification.[6]
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Staging

The Masaoka system is the most commonly accepted staging system for thymomas (see Table 3 below).

Table 3. Masaoka Staging System of Thymomas and Corresponding Therapy (Open Table in a new window)

Stage Definition Treatment
I Encapsulated tumor with no gross or microscopic invasion Complete surgical excision
II Macroscopic invasion into the mediastinal fat or pleura or microscopic invasion into the capsule Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence
III Invasion of the pericardium, great vessels, or lung Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence
IVA Pleural or pericardial metastatic spread Surgical debulking, radiotherapy, and chemotherapy
IVB Pleural or pericardial metastatic spread Surgical debulking, radiotherapy, and chemotherapy

See Thymoma Staging for more information.

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Contributor Information and Disclosures
Author

Kendrix J Evans, MD, MS Resident Physician, Department of General Surgery, University of Utah School of Medicine

Kendrix J Evans, MD, MS is a member of the following medical societies: American College of Surgeons, American Medical Association, American Medical Student Association/Foundation, Association of Military Surgeons of the US, Christian Medical and Dental Associations

Disclosure: Nothing to disclose.

Coauthor(s)

A Letch Kline, MD Chief, Academic Affliations, Gulf Coast Veterans Health Care System; Clinical Assistant Professor, Department of Surgery, Uniformed Services University of the Health Sciences, F Edward Hebert School of Medicine

A Letch Kline, MD is a member of the following medical societies: American College of Chest Physicians, American College of Surgeons, Southeastern Surgical Congress

Disclosure: Nothing to disclose.

Quintessa Miller, MD 

Quintessa Miller, MD is a member of the following medical societies: American College of Surgeons, National Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

John Geibel, MD, DSc, MSc, MA Vice Chair and Professor, Department of Surgery, Section of Gastrointestinal Medicine, and Department of Cellular and Molecular Physiology, Yale University School of Medicine; Director, Surgical Research, Department of Surgery, Yale-New Haven Hospital; American Gastroenterological Association Fellow

John Geibel, MD, DSc, MSc, MA is a member of the following medical societies: American Gastroenterological Association, American Physiological Society, American Society of Nephrology, Association for Academic Surgery, International Society of Nephrology, New York Academy of Sciences, Society for Surgery of the Alimentary Tract

Disclosure: Received royalty from AMGEN for consulting; Received ownership interest from Ardelyx for consulting.

Additional Contributors

Juan B Ochoa, MD Assistant Professor, Department of Surgery, University of Pittsburgh School of Medicine; Medical and Scientific Director, HCN, Nestle Healthcare Nutrition

Disclosure: Nothing to disclose.

Acknowledgements

Michael A Grosso, MD Consulting Staff, Department of Cardiothoracic Surgery, St Francis Hospital

Michael A Grosso, MD is a member of the following medical societies: American College of Surgeons, Society of Thoracic Surgeons, and Society of University Surgeons

Disclosure: Nothing to disclose.

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Anatomy of thymus, with emphasis on blood supply and relation to recurrent laryngeal and phrenic nerves.
Lateral view of thymus. Thymic arteries are derived from adjacent internal mammary arteries; inferior thymic vein empties into innominate vein. Thymus gland's surrounding vascular and neural structures may be invaded during spread of thymoma.
CT scan clearly illustrates mass in right anterolateral mediastinum.
Table 1. Survival of Thymoma by Stage: Memorial Sloan-Kettering Experience
Stage 5-Year Survival 10-Year Survival
I 90% 80%
II 90% 80%
III 60% 30%
IV Less than 25% N/A
Table 2. World Health Organization (WHO) Pathologic Classification and Associated Prognostic Categories
Type Histologic Description Disease-Free Survival at 10 years,* %
A Medullary thymoma 100
AB Mixed thymoma 100
B1 Predominantly cortical thymoma 83
B2 Cortical thymoma 83
B3 Well-differentiated thymic carcinoma 35
C Thymic carcinoma 28
*Series of 100 thymomas resected in Japan between 1973 and 2001 using WHO classification.[6]
Table 3. Masaoka Staging System of Thymomas and Corresponding Therapy
Stage Definition Treatment
I Encapsulated tumor with no gross or microscopic invasion Complete surgical excision
II Macroscopic invasion into the mediastinal fat or pleura or microscopic invasion into the capsule Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence
III Invasion of the pericardium, great vessels, or lung Complete surgical excision and postoperative radiotherapy to decrease the incidence of local recurrence
IVA Pleural or pericardial metastatic spread Surgical debulking, radiotherapy, and chemotherapy
IVB Pleural or pericardial metastatic spread Surgical debulking, radiotherapy, and chemotherapy
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