Difference between revisions of "Thymus"

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'''Thymus''' is an annoying little organ that is in the [[mediastinum]]. It is often removed in pediatric cardiac surgery 'cause it is in the way.  In adults, it is commonly removed 'cause the patient has myasthenia gravis.
[[Image:Thymic corpuscle.jpg|thumb|right|225px|[[Micrograph]] of a thymic corpusle (Hassall's corpusle). [[H&E stain]].]]
'''Thymus''' is a little organ that is in the [[mediastinum]]. It is often removed in pediatric cardiac surgery 'cause it is in the way.  In adults, it is commonly removed 'cause the patient has myasthenia gravis.


=Overview=
=Overview=
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*One of two ''[[primary lymphoid organs]]'' - the other one is the [[bone marrow]].<ref>URL: [http://www.life.umd.edu/classroom/bsci423/song/Lab1.html http://www.life.umd.edu/classroom/bsci423/song/Lab1.html]. Accessed on: 28 March 2012.</ref>
*One of two ''[[primary lymphoid organs]]'' - the other one is the [[bone marrow]].<ref>URL: [http://www.life.umd.edu/classroom/bsci423/song/Lab1.html http://www.life.umd.edu/classroom/bsci423/song/Lab1.html]. Accessed on: 28 March 2012.</ref>
*Thymus involutes after childhood.
*Thymus involutes after childhood.
**The line between ''[[thymoma]]'' and ''persistent normal thymus in the adult'' is not well-defined in the radiologic context.<ref name=pmid25925358>{{Cite journal  | last1 = Araki | first1 = T. | last2 = Nishino | first2 = M. | last3 = Gao | first3 = W. | last4 = Dupuis | first4 = J. | last5 = Hunninghake | first5 = GM. | last6 = Murakami | first6 = T. | last7 = Washko | first7 = GR. | last8 = O'Connor | first8 = GT. | last9 = Hatabu | first9 = H. | title = Normal thymus in adults: appearance on CT and associations with age, sex, BMI and smoking. | journal = Eur Radiol | volume = 26 | issue = 1 | pages = 15-24 | month = Jan | year = 2016 | doi = 10.1007/s00330-015-3796-y | PMID = 25925358 }}</ref>
*May be absent due to genetic abnormalities, e.g. [[DiGeorge syndrome]].
*May be absent due to genetic abnormalities, e.g. [[DiGeorge syndrome]].


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Anatomically in contact with:  
Anatomically in contact with:  
*Pericardium.
*[[Pericardium]].
*Medistinal pleural.
*Medistinal pleural.


==Normal histology==
==Normal histology==
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==IHC and thymus==
==IHC and thymus==
Types A, AB, B:<ref>CJS. January 2010.</ref>
Types A, AB, B:<ref name=cjs>CJS. January 2010.</ref>
*CK7-, CK20-, CAM5.2+, CK5/6+, p63+, CD5-.
*[[CK7]] -ve, [[CK20]] -ve, CAM5.2 +ve, [[CK5/6]] +ve, [[p63]] +ve, CD5 -ve.


Type C:<ref>CJS. January 2010.</ref>
Type C:
*CD5+.
*CD5 +ve.<ref name=cjs>CJS. January 2010.</ref> (???)
*D2-40 +ve.<ref name=pmid24649128>{{Cite journal  | last1 = Yokota | first1 = K. | last2 = Tateyama | first2 = H. | last3 = Yano | first3 = M. | last4 = Moriyama | first4 = S. | last5 = Hikosaka | first5 = Y. | last6 = Okuda | first6 = K. | last7 = Shitara | first7 = M. | last8 = Okumura | first8 = M. | last9 = Yokoi | first9 = K. | title = Clinicopathological analysis of small-sized thymoma with podoplanin and Ki 67 expression analysis. | journal = Mol Clin Oncol | volume = 1 | issue = 1 | pages = 88-92 | month = Jan | year = 2013 | doi = 10.3892/mco.2012.2 | PMID = 24649128 }}</ref>


All types:<ref>CJS. January 2010.</ref>
All types:<ref name=cjs>CJS. January 2010.</ref>
*CD1a (immature T cells, Langerhans cells, dendritic cells<ref>URL: [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf]. Accessed on: 26 August 2010.</ref>), CEA +ve (focal), vimentin -ve.
*CD1a +ve (immature T cells, Langerhans cells, dendritic cells<ref>URL: [http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf]. Accessed on: 26 August 2010.</ref>), CEA +ve (focal), vimentin -ve.


Others (immature T cells):
Others (immature T cells):
*TdT.
*TdT +ve.
*CD99.
*CD99 +ve.


==Anterior mediastinum mass DDx==
==Anterior mediastinum mass DDx==
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Associations:<ref name=Ref_PBoD707-8>{{Ref PBoD|707-8}}</ref>   
Associations:<ref name=Ref_PBoD707-8>{{Ref PBoD|707-8}}</ref>   
*Myasthenia gravis.
*Myasthenia gravis.
*Graves' diseases.
*[[Graves' disease]].
*[[Systemic lupus erythematosus]] (SLE).
*[[Systemic lupus erythematosus]] (SLE).
*[[Rheumatoid arthritis]].
*[[Rheumatoid arthritis]].
*Other autoimmune diseases.
*Other [[autoimmune diseases]].


==Thymoma==
==Thymoma==
===General===
{{Main|Thymoma}}
*Strong association with autoimmune disease, esp. myasthenia gravis.
 
====Classification====
The ''WHO'' published a widely used system - WHO classification:<ref>{{Ref Sternberg4|1264}}</ref>
=====Type A=====
*AKA ''Spindle cell'' or ''medullary''.
*Arise from ''medullary epithelial cells''.
*Good prognosis.
 
IHC:
*Usu. keratin+.
=====Type AB=====
*Like Type A... but with foci of lymphocytes.
=====Type B1=====
*Near normal, expanded cortex.
 
Lesion consists of:
*>2/3 lymphocytes, <1/3 cortical epithelial cells.
=====Type B2=====
*Neoplastic cells with some resemblance to cortical epithelial cells.
**Epithelioid cells with distinct nucleoli.
**May be perivascular.
*Large population of lymphocytes.
 
Lesion consists of:
*<2/3 but >1/3 lymphocytes, >1/3 but <2/3 cortical epithelial cells.
 
Notes:
*Most common '''B''' type.
=====Type B3=====
*Neoplastic cells with some resemblance to cortical epithelial cells.
**Polygonal/round shape.
**Form sheets (of cells) - '''key feature'''.
*Lymphocytes - less than in Type B2.
*AKA ''well-differentiated thymic carcinoma''.
 
Lesion consists of:
*<1/3 lymphocytes, >2/3 cortical epithelial cells.
 
Note:
*Neoplastic cells derived from the thymus with cytologic features of malignancy are [[thymic carcinoma]]s.
 
Images:
<gallery>
Image:Thymoma_type_B1_(1).JPG | Thymoma Type B1. (WC/KGH)
Image:Thymoma_B1_(2).JPG | Thymoma Type B1. (WC/KGH)
Image:Thymoma_B1_(3)_CK_CAM5-2.JPG | Thymoma Type B1 - CAM5.2. (WC/KGH)
</gallery>
 
===Gross===
*Light brown/tan.
*Encapsulated.
 
Image:
*[http://www.sciencephoto.com/media/253251/enlarge Thymoma (sciencephoto.com)].
 
===Microscopic===
Features:
*Lymphocytes.
*Spindle cells.
 
DDx:
*[[Squamous cell carcinoma]].
*[[Lymphoma]].
 
Images:
*[http://commons.wikimedia.org/wiki/File:Thymoma_B1_%282%29.JPG Thymoma (WC)].
 
===Staging===
There is a system by Masaoka and colleagues.<ref name=pmid7296496 >{{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>


==Metaplastic thymoma==
==Metaplastic thymoma==
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DDx:
DDx:
*[[Thymic carcinoma]] with sarcomatoid differentiation.
*[[Thymic carcinoma]] with sarcomatoid differentiation.
====Images====
www:
*[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3479700/figure/F1/ Metaplastic thymoma (nih.gov)].<ref>{{Cite journal  | last1 = Kang | first1 = G. | last2 = Yoon | first2 = N. | last3 = Han | first3 = J. | last4 = Kim | first4 = YE. | last5 = Kim | first5 = TS. | last6 = Kim | first6 = K. | title = Metaplastic thymoma: report of 4 cases. | journal = Korean J Pathol | volume = 46 | issue = 1 | pages = 92-5 | month = Feb | year = 2012 | doi = 10.4132/KoreanJPathol.2012.46.1.92 | PMID = 23109986 }}
</ref>


===IHC===
===IHC===
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==Thymic carcinoma==
==Thymic carcinoma==
*AKA ''Thymic tumour type C''.
{{Main|Thymic carcinoma}}
===General===
*Rare.
*Usually arise ''de novo'', i.e. thymoma is not generally a precursor.
 
===Microscopic===
Features:<ref name=Ref_WMSP147>{{Ref WMSP|147}}</ref>
*Cytologically malignant - variable morphology.
*+/-Squamous differentiation.
 
Notes:
*Staging depends on capsular invasion.
 
DDx:
*[[Thymoma]].
*[[Lung cancer|Lung carcinoma]].
 
Images:
*[http://www.webpathology.com/image.asp?n=1&Case=653 Thymic carcinoma - low mag. (webpathology.com)].
*[http://www.webpathology.com/image.asp?n=2&Case=653 Thymic carcinoma - high mag. (webpathology.com)].
*[http://www.webpathology.com/image.asp?n=4&Case=653 Thymic carcinoma - lymphoepithelioma-like - high mag. (webpathology.com)].
 
===IHC===
Features:<ref name=Ref_WMSP147>{{Ref WMSP|147}}</ref>
*CD5 +ve.<ref name=Ref_PBoD708>{{Ref PBoD|708}}</ref>
*CD7+ve.
*CD117 +ve.
*TTF-1 -ve.


=See also=
=See also=

Latest revision as of 17:02, 6 May 2019

Micrograph of a thymic corpusle (Hassall's corpusle). H&E stain.

Thymus is a little organ that is in the mediastinum. It is often removed in pediatric cardiac surgery 'cause it is in the way. In adults, it is commonly removed 'cause the patient has myasthenia gravis.

Overview

General

  • Important for development of the immune system.
  • One of two primary lymphoid organs - the other one is the bone marrow.[1]
  • Thymus involutes after childhood.
    • The line between thymoma and persistent normal thymus in the adult is not well-defined in the radiologic context.[2]
  • May be absent due to genetic abnormalities, e.g. DiGeorge syndrome.

Anatomy

Location:

Anatomically in contact with:

Normal histology

General

Features:[3]

  • No germinal centres.
  • Hassall's corpusle (thymic corpusle).
    • Round eosinophilic thingy.
    • Thought to arise from medullary epithelial cells (see cell types).[4]

Note:

Cell types

Cells of the thymus (short version):

  1. Cortical epithelial cells.[4]
    • Epithelioid.
    • Abundant cytoplasm.
    • Pale nuclei with small nucleoli.
  2. Medullary epithelial cells.[4]
    • Spindle morphology.
    • Scant cytoplasm.
    • Oval dark nuclei.
  3. T lymphocytes.

Other cells:

  • Macrophages.
  • Dendritic cells.
  • Other WBCs: B lymphocytes, neutrophils, eosinophils.
  • Myoid cells.

Note:

  • Thymic tumours are derived from the epithelial component of the thymus, i.e. the cortical epithelial cells and medullary epithelial cells.

Images

  • Thymic corpusle. (WC/Nephron)

IHC and thymus

Types A, AB, B:[5]

Type C:

  • CD5 +ve.[5] (???)
  • D2-40 +ve.[6]

All types:[5]

  • CD1a +ve (immature T cells, Langerhans cells, dendritic cells[7]), CEA +ve (focal), vimentin -ve.

Others (immature T cells):

  • TdT +ve.
  • CD99 +ve.

Anterior mediastinum mass DDx

Main article: Mediastinum

4 Ts (mnemonic):

Thymus and stress

  • Stress -> increased endogenous steroid -> lymphocyte death -> increased tingible body macrophages.[8]

Specific conditions

Thymic follicular hyperplasia

  • AKA thymic follicular hyperplasia.

Features:[9]

  • Follicular centres in the thymus.

Associations:[9]

Thymoma

Main article: Thymoma

Metaplastic thymoma

  • AKA thymoma with pseudosarcomatous stroma.[10]

General

Microscopic

Features:[10]

  1. Epithelioid cells.
  2. Spindle cells.
  • Few lymphocytes.

DDx:

Images

www:

IHC

CD5 -ve.[10]

Thymic carcinoma

Main article: Thymic carcinoma

See also

References

  1. ↑ URL: http://www.life.umd.edu/classroom/bsci423/song/Lab1.html. Accessed on: 28 March 2012.
  2. ↑ Araki, T.; Nishino, M.; Gao, W.; Dupuis, J.; Hunninghake, GM.; Murakami, T.; Washko, GR.; O'Connor, GT. et al. (Jan 2016). "Normal thymus in adults: appearance on CT and associations with age, sex, BMI and smoking.". Eur Radiol 26 (1): 15-24. doi:10.1007/s00330-015-3796-y. PMID 25925358.
  3. ↑ URL: http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm. Accessed on: 17 June 2010.
  4. ↑ 4.0 4.1 4.2 4.3 Cotran, Ramzi S.; Kumar, Vinay; Fausto, Nelson; Nelso Fausto; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease (7th ed.). St. Louis, Mo: Elsevier Saunders. pp. 706. ISBN 0-7216-0187-1.
  5. ↑ 5.0 5.1 5.2 CJS. January 2010.
  6. ↑ Yokota, K.; Tateyama, H.; Yano, M.; Moriyama, S.; Hikosaka, Y.; Okuda, K.; Shitara, M.; Okumura, M. et al. (Jan 2013). "Clinicopathological analysis of small-sized thymoma with podoplanin and Ki 67 expression analysis.". Mol Clin Oncol 1 (1): 88-92. doi:10.3892/mco.2012.2. PMID 24649128.
  7. ↑ URL: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf. Accessed on: 26 August 2010.
  8. ↑ Toti P, De Felice C, Stumpo M, et al. (September 2000). "Acute thymic involution in fetuses and neonates with chorioamnionitis". Hum. Pathol. 31 (9): 1121–8. PMID 11014581.
  9. ↑ 9.0 9.1 Cotran, Ramzi S.; Kumar, Vinay; Fausto, Nelson; Nelso Fausto; Robbins, Stanley L.; Abbas, Abul K. (2005). Robbins and Cotran pathologic basis of disease (7th ed.). St. Louis, Mo: Elsevier Saunders. pp. 707-8. ISBN 0-7216-0187-1.
  10. ↑ 10.0 10.1 10.2 URL: http://surgpathcriteria.stanford.edu/thymus/thymoma/metaplastic_thymoma.html. Accessed on: 22 December 2011.
  11. ↑ 11.0 11.1 Lu, HS.; Gan, MF.; Zhou, T.; Wang, SZ. (Oct 2011). "Sarcomatoid thymic carcinoma arising in metaplastic thymoma: a case report.". Int J Surg Pathol 19 (5): 677-80. doi:10.1177/1066896909355458. PMID 20034984.
  12. ↑ Kang, G.; Yoon, N.; Han, J.; Kim, YE.; Kim, TS.; Kim, K. (Feb 2012). "Metaplastic thymoma: report of 4 cases.". Korean J Pathol 46 (1): 92-5. doi:10.4132/KoreanJPathol.2012.46.1.92. PMID 23109986.
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