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==Overview==
==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 carcinoma]]thymoma
* Thymoma is the most common tumor of the anterior [[mediastinum]], consisting of any type of thymic [[epithelial cell]] as well as [[lymphocyte]]s 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.
* Thymomas associated with autoimmune disorders usually are benign. Malignant thymomas can [[metastasis|metastasize]], generally to [[pleura]], [[kidney]], [[bone]], [[liver]], or [[brain]].


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 carcinoma]]thymoma
Thymoma is the most common tumor of the anterior [[mediastinum]], consisting of any type of thymic [[epithelial cell]] as well as [[lymphocyte]]s 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.<ref name=Thomas1999>{{cite journal |author=Thomas CR, Wright CD, Loehrer PJ |title=Thymoma: state of the art |journal=J. Clin. Oncol. |volume=17 |issue=7 |pages=2280–9 |year=1999 |pmid=10561285 |doi=}}</ref>
Thymomas associated with autoimmune disorders usually are benign. Malignant thymomas can [[metastasis|metastasize]], generally to [[pleura]], [[kidney]], [[bone]], [[liver]] or [[brain]].<ref name="pmid10561285">{{cite journal |author=Thomas CR, Wright CD, Loehrer PJ |title=Thymoma: state of the art |journal=[[Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology]] |volume=17 |issue=7 |pages=2280–9 |year=1999 |month=July |pmid=10561285 |doi= |url=http://www.jco.org/cgi/pmidlookup?view=long&pmid=10561285 |accessdate=2012-01-18}}</ref>
==Historical Perspective==
==Historical Perspective==
The thymic epithelial tumors staging was initially proposed by Bergh and his colleagues in 1978,<ref name="Bergh-1978">{{Cite journal  | last1 = Bergh | first1 = NP. | last2 = Gatzinsky | first2 = P. | last3 = Larsson | first3 = S. | last4 = Lundin | first4 = P. | last5 = Ridell | first5 = B. | title = Tumors of the thymus and thymic region: I. Clinicopathological studies on thymomas. | journal = Ann Thorac Surg | volume = 25 | issue = 2 | pages = 91-8 | month = Feb | year = 1978 | doi =  | PMID = 626543 }}</ref>modified by Wilkins and Castleman in 1979,<ref name="Wilkins-1979">{{Cite journal  | last1 = Wilkins | first1 = EW. | last2 = Castleman | first2 = B. | title = Thymoma: a continuing survey at the Massachusetts General Hospital. | journal = Ann Thorac Surg | volume = 28 | issue = 3 | pages = 252-6 | month = Sep | year = 1979 | doi =  | PMID = 485626 }}</ref>and advanced by Masaoka et al. in 1981.<ref name="Masaoka-1981">{{Cite journal  | last1 = Masaoka | first1 = A. | last2 = Monden | first2 = Y. | last3 = Nakahara | first3 = K. | last4 = Tanioka | first4 = T. | title = Follow-up study of thymomas with special reference to their clinical stages. | journal = Cancer | volume = 48 | issue = 11 | pages = 2485-92 | month = Dec | year = 1981 | doi =  | PMID = 7296496 }}</ref><ref name="Kondo-2005">{{Cite journal  | last1 = Kondo | first1 = K. | title = Invited commentary. | journal = Ann Thorac Surg | volume = 80 | issue = 6 | pages = 2000-1 | month = Dec | year = 2005 | doi = 10.1016/j.athoracsur.2005.08.053 | PMID = 16305832 }}</ref>
* The thymic epithelial tumors staging was initially proposed by Bergh and his colleagues in 1978, modified by Wilkins and Castleman in 1979, and advanced by Masaoka et al. in 1981.


==Classification==
==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.<ref>{{Cite web  | last =  | first =  | title = http://www.iarc.fr/en/publications/pdfs-online/pat-gen/bb10/BB10.pdf | url = http://www.iarc.fr/en/publications/pdfs-online/pat-gen/bb10/BB10.pdf | publisher =  | date =  | accessdate = }}</ref>
* 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.


==Pathology==
==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.
* 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 [[cytoplasm]]s, and fat droplets are characteristic findings of thymoma.


==Causes==
==Causes==
There are no established causes for thymoma.
* There are no established causes for thymoma.
 
==Differential Diagnosis==
==Differential Diagnosis==
Thymoma must be differentiated from other thymic diseases such as [[thymic carcinoma]], thymic [[cyst]], thymic [[hyperplasia]] and [[germ cell tumors]].
Thymoma must be differentiated from other thymic diseases such as
* [[thymic carcinoma]]
* Thymic [[cyst]]
* Thymic [[hyperplasia]]  
* [[germ cell tumors]].
 
==Epidemiology and Demographic==
==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.
* 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==
==Risk Factors==
There are no established risk factors for thymoma.<ref name="Engels-2010">{{Cite journal  | last1 = Engels | first1 = EA. | title = Epidemiology of thymoma and associated malignancies. | journal = J Thorac Oncol | volume = 5 | issue = 10 Suppl 4 | pages = S260-5 | month = Oct | year = 2010 | doi = 10.1097/JTO.0b013e3181f1f62d | PMID = 20859116 }}</ref>
* There are no established risk factors for thymoma.
 
==Natural History, Complication and Prognosis==
==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.
* 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.
* 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==
==Diagnosis==
===History and symptoms===
===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]].
Symptoms of thymoma include  
* [[muscle weakness]]
* [[cough]]
* [[wheezing]]
* [[dysphagia]].
In addition to the symptoms of associated immune syndromes such as,
* [[anemia]]
* [[arthralgia]]
* [[skin rash]].
 
===Physical examination===
===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]].
Patients with thymoma usually appear asymptomatic. Physical examination of patients with thymoma is may be remarkable for,
* Neck lump,  
* Facial [[swelling]]  
* [[wheezing]].
 
===Staging===
===Staging===
Staging of thymic epithelial tumors was initially proposed by Bergh and his colleagues in 1978,<ref name="Bergh-1978">{{Cite journal  | last1 = Bergh | first1 = NP. | last2 = Gatzinsky | first2 = P. | last3 = Larsson | first3 = S. | last4 = Lundin | first4 = P. | last5 = Ridell | first5 = B. | title = Tumors of the thymus and thymic region: I. Clinicopathological studies on thymomas. | journal = Ann Thorac Surg | volume = 25 | issue = 2 | pages = 91-8 | month = Feb | year = 1978 | doi =  | PMID = 626543 }}</ref> modified by Wilkins and Castleman in 1979,<ref name="Wilkins-1979">{{Cite journal  | last1 = Wilkins | first1 = EW. | last2 = Castleman | first2 = B. | title = Thymoma: a continuing survey at the Massachusetts General Hospital. | journal = Ann Thorac Surg | volume = 28 | issue = 3 | pages = 252-6 | month = Sep | year = 1979 | doi =  | PMID = 485626 }}</ref> and advanced by Masaoka et al. in 1981.<ref name="Masaoka-1981">{{Cite journal  | last1 = Masaoka | first1 = A. | last2 = Monden | first2 = Y. | last3 = Nakahara | first3 = K. | last4 = Tanioka | first4 = T. | title = Follow-up study of thymomas with special reference to their clinical stages. | journal = Cancer | volume = 48 | issue = 11 | pages = 2485-92 | month = Dec | year = 1981 | doi =  | PMID = 7296496 }}</ref><ref name="Kondo-2005">{{Cite journal  | last1 = Kondo | first1 = K. | title = Invited commentary. | journal = Ann Thorac Surg | volume = 80 | issue = 6 | pages = 2000-1 | month = Dec | year = 2005 | doi = 10.1016/j.athoracsur.2005.08.053 | PMID = 16305832 }}</ref> Modified Masaoka staging grouped with TNM classification is the most widely adopted system for thymic epithelial tumors currently in use.
* Staging of thymic epithelial tumors was initially proposed by Bergh and his colleagues in 1978, modified by Wilkins and Castleman in 1979, and advanced by Masaoka et al. in 1981.  
* Modified Masaoka staging grouped with TNM classification is the most widely adopted system for thymic epithelial tumors currently in use.
 
===Laboratory Findings===
===Laboratory Findings===
Laboratory findings associated with thymoma may include [[antibodies]] to the [[acetylcholine receptor]], abnormal [[electrolyte]]s, [[renal]], and [[liver function]] tests.
Laboratory findings associated with thymoma may include,
* A[[antibodies|ntibodies]] to the [[acetylcholine receptor]],  
* Abnormal [[electrolyte]]s, [[renal]], and [[liver function]] tests.
 
===X-Ray===
===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.
* 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===
===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.
* [[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===
===MRI===
On [[thoracic]] MRI, thymoma is characterized by increased heterogenous signal on T2WI.
* On [[thoracic]] MRI, thymoma is characterized by increased heterogenous signal on T2WI.
 
===Ultrasound===
===Ultrasound===
Ultrasound is used to guide fine needle aspiration or core needle biopsy in patients with thymoma.
* Ultrasound is used to guide [[fine needle aspiration]] or core [[needle biopsy]] in patients with thymoma.
 
===Other Imaging Studies===
===Other Imaging Studies===
[[PET scan]] may be used in the diagnosis of thymoma.
* [[PET scan]] may be used in the diagnosis of thymoma.
 
===Other Diagnostic Studies===
===Other Diagnostic Studies===
Other diagnostic studies for Thymoma include CT scan guided core needle [[biopsy]], CT scan guided [[fine needle aspiration]], [[mediastinoscopy]] and videothoracoscopy.
Other diagnostic studies for Thymoma include  
* CT scan guided core needle [[biopsy]]
* CT scan guided [[fine needle aspiration]]
* [[mediastinoscopy]]
* Videothoracoscopy.
 
==Treatment==
==Treatment==
===Medical Therapy===
===Medical Therapy===
Chemotherapy and radiotherapy are used as [[adjuvant therapy|adjuvant]] or [[neoadjuvant therapy|neoadjuvant therapies]]. Neoadjuvant therpy may be administered prior to surgery to make the tumor resectable.
* [[Chemotherapy]] and [[radiotherapy]] are used as [[adjuvant therapy|adjuvant]] or [[neoadjuvant therapy|neoadjuvant therapies]].  
* Neoadjuvant therpy may be administered prior to surgery to make the tumor resectable.
 
===Surgery===
===Surgery===
Surgery is the mainstay of treatment of thymoma.
* Surgery is the mainstay of treatment of thymoma.
===Radiotherapy===
 
[[Radiation therapy]] may be used in the 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==
==References==
{{Reflist|2}}
{{Reflist|2}}
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Latest revision as of 23:11, 31 May 2019

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IEditor-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.
  • Thymomas associated with autoimmune disorders usually are benign. Malignant thymomas can metastasize, generally to pleura, kidney, bone, liver, or brain.

Historical Perspective

  • The thymic epithelial tumors staging was initially proposed by Bergh and his colleagues in 1978, modified by Wilkins and Castleman in 1979, and advanced by Masaoka et al. in 1981.

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.

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

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.

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.
  • 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

In addition to the symptoms of associated immune syndromes such as,

Physical examination

Patients with thymoma usually appear asymptomatic. Physical examination of patients with thymoma is may be remarkable for,

Staging

  • Staging of thymic epithelial tumors was initially proposed by Bergh and his colleagues in 1978, modified by Wilkins and Castleman in 1979, and advanced by Masaoka et al. in 1981.
  • 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,

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

Other Imaging Studies

  • PET scan may be used in the diagnosis of thymoma.

Other Diagnostic Studies

Other diagnostic studies for Thymoma include

Treatment

Medical Therapy

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

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