Thymoma overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Amr Marawan, M.D. [2] Ahmad Al Maradni, M.D. [3]
Overview
Thymoma is a benign thymic neoplasm located in the anterior mediastinum, behind the sternum and in front of the great vessels that involutes during puberty, it takes part in lymphocytes maturation throughout adulthood. The incidence of thymoma is approximately 0.13 per 100,000 individuals.
Thymic neoplasm can be divided into two major groups: thymoma and thymic carcinomathymoma
Thymoma is the most common tumor of the anterior mediastinum, consisting of any type of thymic epithelial cell as well as lymphocytes that are usually abundant and probably not neoplastic. Thymoma usually is benign, and frequently encapsulated uncommon tumor, best known for its association with the autoimmune disorder such as myasthenia gravis. Thymoma is found in 15% of patients with myasthenia gravis. Once diagnosed, thymomas may be removed surgically. If left untreated thymoma may progress to invade the mediastinum and the surrounding structure. Depending on the stage of the tumor at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as good. Common complications of the thymoma include the pressure effect of the mass itself, autoimmune diseases, and rarely, malignancy. Metastasis is extremely rare. In the rare case of a malignant tumor, chemotherapy may be used.
Malignant lymphomas that involve the thymus, e.g., lymphosarcoma, Hodgkin's disease (termed "granulomatous thymoma" in the past), should not be regarded as thymoma.[1]
Thymomas associated with autoimmune disorders usually are benign. Malignant thymomas can metastasize, generally to pleura, kidney, bone, liver, or brain.[2]
Historical Perspective
The thymic epithelial tumors staging was initially proposed by Bergh and his colleagues in 1978,[3]modified by Wilkins and Castleman in 1979,[4]and advanced by Masaoka et al. in 1981.[5][6]
Classification
In 1999, a World Health Organization (WHO) Working group suggested a non-committal terminology (Masaoka classification), preserving the distinct categories of the histogenetic classification, but using letters and numbers to designate tumour entities. Recently, it has been very well accepted as it provides an easy comparison of clinical, pathological and immunological studies.[7]
Pathology
On gross pathology, well circumscribed mass, that is locally invasive is a characteristic finding of thymoma. On microscopic histopathological analysis, round cells, with ample vacuolated cytoplasms, and fat droplets are characteristic findings of thymoma.
Causes
There are no established causes for thymoma.
Differential Diagnosis
Thymoma must be differentiated from other thymic diseases such as thymic carcinoma, thymic cyst, thymic hyperplasia and germ cell tumors.
Epidemiology and Demographic
The incidence of thymoma is approximately 0.13 per 100,000 individuals. Thymic neoplasms are the most common tumors located in the anterior mediastinum (20%). Incidence increases in middle age, and peaks in the seventh decade of life. Men and women are equally affected.
Risk Factors
There are no established risk factors for thymoma.[8]
Natural History, Complication and Prognosis
If left untreated thymoma may progress to invade the mediastinum and the surrounding structure. Depending on the stage of the tumor at the time of diagnosis, the prognosis may vary. However, the prognosis is generally regarded as good. Common complications of the thymoma include the pressure effect of the mass itself, autoimmune diseases, and rarely, malignancy.
Diagnosis
History and symptoms
Symptoms of thymoma include muscle weakness, cough, wheezing, and dysphagia. In addition to the symptoms of associated immune syndromes such as anemia, arthralgia, and skin rash.
Physical examination
Patients with thymoma usually appear asymptomatic. Physical examination of patients with thymoma is may be remarkable for neck lump, facial swelling and wheezing.
Staging
Staging of thymic epithelial tumors was initially proposed by Bergh and his colleagues in 1978,[3] modified by Wilkins and Castleman in 1979,[4] and advanced by Masaoka et al. in 1981.[5][6] Modified Masaoka staging grouped with TNM classification is the most widely adopted system for thymic epithelial tumors currently in use.
Laboratory Findings
Laboratory findings associated with thymoma may include antibodies to the acetylcholine receptor, abnormal electrolytes, renal, and liver function tests.
X-Ray
On chest x-ray, thymoma is characterized by oval to rounded, well demarcated, asymmetric, homogeneous mass of soft tissue density on one side of the midline.
CT Scan
Computed Tomography scan may be diagnostic of thymoma. The tumor is generally located inside the thymus, and can be calcified. Increased vascular enhancement can be indicative of malignancy, as can be pleural deposits.
MRI
On thoracic MRI, thymoma is characterized by increased heterogenous signal on T2WI.
Ultrasound
Ultrasound is used to guide fine needle aspiration or core needle biopsy in patients with thymoma.
Other Imaging Studies
PET scan may be used in the diagnosis of thymoma.
Other Diagnostic Studies
Other diagnostic studies for Thymoma include CT scan guided core needle biopsy, CT scan guided fine needle aspiration, mediastinoscopy and videothoracoscopy.
Treatment
Medical Therapy
Chemotherapy and radiotherapy are used as adjuvant or neoadjuvant therapies. Neoadjuvant therpy may be administered prior to surgery to make the tumor resectable.
Surgery
Surgery is the mainstay of treatment of thymoma.
Primary Prevention
There are no primary preventive measures available for thymoma.
Secondary Prevention
Complete surgical resection may help to prevent the recurrence of thymoma.
References
- ↑ Thomas CR, Wright CD, Loehrer PJ (1999). "Thymoma: state of the art". J. Clin. Oncol. 17 (7): 2280–9. PMID 10561285.
- ↑ Thomas CR, Wright CD, Loehrer PJ (1999). "Thymoma: state of the art". Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. 17 (7): 2280–9. PMID 10561285. Retrieved 2012-01-18. Unknown parameter
|month=ignored (help) - ↑ 3.0 3.1 Bergh, NP.; Gatzinsky, P.; Larsson, S.; Lundin, P.; Ridell, B. (1978). "Tumors of the thymus and thymic region: I. Clinicopathological studies on thymomas". Ann Thorac Surg. 25 (2): 91–8. PMID 626543. Unknown parameter
|month=ignored (help) - ↑ 4.0 4.1 Wilkins, EW.; Castleman, B. (1979). "Thymoma: a continuing survey at the Massachusetts General Hospital". Ann Thorac Surg. 28 (3): 252–6. PMID 485626. Unknown parameter
|month=ignored (help) - ↑ 5.0 5.1 Masaoka, A.; Monden, Y.; Nakahara, K.; Tanioka, T. (1981). "Follow-up study of thymomas with special reference to their clinical stages". Cancer. 48 (11): 2485–92. PMID 7296496. Unknown parameter
|month=ignored (help) - ↑ 6.0 6.1 Kondo, K. (2005). "Invited commentary". Ann Thorac Surg. 80 (6): 2000–1. doi:10.1016/j.athoracsur.2005.08.053. PMID 16305832. Unknown parameter
|month=ignored (help) - ↑ "http://www.iarc.fr/en/publications/pdfs-online/pat-gen/bb10/BB10.pdf" (PDF). External link in
|title=(help) - ↑ Engels, EA. (2010). "Epidemiology of thymoma and associated malignancies". J Thorac Oncol. 5 (10 Suppl 4): S260–5. doi:10.1097/JTO.0b013e3181f1f62d. PMID 20859116. Unknown parameter
|month=ignored (help)