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Thymus (view source)

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'''Thymus''' is an annoying little organ that is in the mediastinum.
[[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=
==General==
==General==
*Involutes after childhood.
*Location: anterior mediastinum.
*Important for development of the immune system.
*Important for development of the immune system.
*May contain within it parathyroid.<ref name=Ref_PBoD706>{{Ref PBoD|706}}</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.
**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]].


==Histology==
==Anatomy==
Location:
*Anterior [[mediastinum]].
 
Anatomically in contact with:
*[[Pericardium]].
*Medistinal pleural.
 
==Normal histology==
===General===
===General===
Features:<ref>URL: [http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm]. Accessed on: 17 June 2010.</ref>
Features:<ref>URL: [http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm]. Accessed on: 17 June 2010.</ref>
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**Round eosinophilic thingy.
**Round eosinophilic thingy.
**Thought to arise from medullary epithelial cells (see ''cell types'').<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>
**Thought to arise from medullary epithelial cells (see ''cell types'').<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>
Note:
*The thymus may contain within it [[parathyroid]].<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>


===Cell types===
===Cell types===
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*Myoid cells.
*Myoid cells.


Images:
Note:
*[http://commons.wikimedia.org/wiki/File:Thymic_corpuscle.jpg Thymic corpusle (wikimedia.org)].
*Thymic tumours are derived from the epithelial component of the thymus, i.e. the ''cortical epithelial cells'' and ''medullary epithelial cells''.


==Di George syndrome==
====Images====
*Things go wrong with the thymus... very wrong.
<gallery>
Image:Thymic_corpuscle.jpg | Thymic corpusle. (WC/Nephron)
</gallery>
 
==IHC and thymus==
Types A, AB, B:<ref name=cjs>CJS. January 2010.</ref>
*[[CK7]] -ve, [[CK20]] -ve, CAM5.2 +ve, [[CK5/6]] +ve, [[p63]] +ve, CD5 -ve.
 
Type C:
*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 name=cjs>CJS. January 2010.</ref>
*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):
*TdT +ve.
*CD99 +ve.
 
==Anterior mediastinum mass DDx==
{{Main|Mediastinum}}
4 Ts (mnemonic):
*Thymoma.
*Terrible [[lymphoma]].
*[[Teratoma]].
*[[Thyroid]] (ectopic).


==Thymus and stress==
==Thymus and stress==
*Stress -> increased endogenous steroid -> lymphocyte death -> increased tingible body macrophages.<ref>{{cite journal |author=Toti P, De Felice C, Stumpo M, ''et al.'' |title=Acute thymic involution in fetuses and neonates with chorioamnionitis |journal=Hum. Pathol. |volume=31 |issue=9 |pages=1121–8 |year=2000 |month=September |pmid=11014581 |doi= |url=}}</ref>
*Stress -> increased endogenous steroid -> lymphocyte death -> increased tingible body macrophages.<ref>{{cite journal |author=Toti P, De Felice C, Stumpo M, ''et al.'' |title=Acute thymic involution in fetuses and neonates with chorioamnionitis |journal=Hum. Pathol. |volume=31 |issue=9 |pages=1121–8 |year=2000 |month=September |pmid=11014581 |doi= |url=}}</ref>


=Specific conditions=
==Thymic follicular hyperplasia==
==Thymic follicular hyperplasia==
*AKA ''thymic follicular hyperplasia''.
*AKA ''thymic follicular hyperplasia''.
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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]].


==Tumours of the thymus (overview)==
==Thymoma==
Thymic tumours are derived from the epithelial component of the thymus, i.e. the ''cortical epithelial cells'' and ''medullary epithelial cells''.
{{Main|Thymoma}}


The ''WHO'' published a widely used system - WHO classification:<ref>{{Ref Sternberg4|1264}}</ref>
==Metaplastic thymoma==
===Type A===
*[[AKA]] ''thymoma with pseudosarcomatous stroma''.<ref name=metapl_thy/>
*AKA ''Spindle cell'' or ''medullary''.
*Arise from ''medullary epithelial cells''.
*Good prognosis.


IHC:
===General===
*Usu. keratin+.
*Extremely rare - only 17 case reports as of 2011.<ref name=pmid20034984>{{Cite journal  | last1 = Lu | first1 = HS. | last2 = Gan | first2 = MF. | last3 = Zhou | first3 = T. | last4 = Wang | first4 = SZ. | title = Sarcomatoid thymic carcinoma arising in metaplastic thymoma: a case report. | journal = Int J Surg Pathol | volume = 19 | issue = 5 | pages = 677-80 | month = Oct | year = 2011 | doi = 10.1177/1066896909355458 | PMID = 20034984 }}</ref>
===Type AB===
*Two reports of transformation into [[thymic carcinoma]].<ref name=pmid20034984/>
*Like Type A... but with foci of lymphocytes.
===Type B1===
*Near normal, expanded cortex.


Lesion consists of:
===Microscopic===
*>2/3 lymphocytes, <1/3 cortical epithelial cells.
Features:<ref name=metapl_thy>URL: [http://surgpathcriteria.stanford.edu/thymus/thymoma/metaplastic_thymoma.html http://surgpathcriteria.stanford.edu/thymus/thymoma/metaplastic_thymoma.html]. Accessed on: 22 December 2011.</ref>
===Type B2===
#Epithelioid cells.
*Neoplastic cells with some resemblance to cortical epithelial cells.
#Spindle cells.  
**Epithelioid cells with distinct nucleoli.
*Few lymphocytes.
**May be perivascular.
*Large population of lymphocytes.


Lesion consists of:
DDx:
*<2/3 but >1/3 lymphocytes, >1/3 but <2/3 cortical epithelial cells.
*[[Thymic carcinoma]] with sarcomatoid differentiation.


Notes:
====Images====
*Most common '''B''' type.
www:
===Type B3===
*[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 }}
*Neoplastic cells with some resemblance to cortical epithelial cells.
</ref>
**Polygonal/round shape.
**Form sheets (of cells) - '''key feature'''.
*Lymphocytes - less than in Type B2.
*AKA ''well-differentiated thymic carcinoma''.


Lesion consists of:
===IHC===
*<1/3 lymphocytes, >2/3 cortical epithelial cells.
CD5 -ve.<ref name=metapl_thy>URL: [http://surgpathcriteria.stanford.edu/thymus/thymoma/metaplastic_thymoma.html http://surgpathcriteria.stanford.edu/thymus/thymoma/metaplastic_thymoma.html]. Accessed on: 22 December 2011.</ref>
===Type C===
*AKA ''thymic carcinoma''.
*Neoplastic cells with some resemblance to cortical epithelial cells - with cytologic features of malignancy.
**Any nuclear atypia of epithelial thymocytes... puts a tumour into this group.
 
Images:
*Type B1:
**[http://commons.wikimedia.org/wiki/File:Thymoma_type_B1_(1).JPG Thymoma Type B1 (WC)].
**[http://commons.wikimedia.org/wiki/File:Thymoma_B1_(2).JPG Thymoma Type B1 (WC)].
**[http://commons.wikimedia.org/wiki/File:Thymoma_B1_(3)_CK_CAM5-2.JPG Thymoma Type B1 - CAM5.2 (WC)].
*Type C:
**[http://www.pathconsultddx.com/pathCon/diagnosis?pii=S1559-8675(06)70555-1 Thymic carcinoma - Type C (pathconsultddx.com)].


==Thymic carcinoma==
==Thymic carcinoma==
*AKA ''Thymic tumour type C''.
{{Main|Thymic carcinoma}}
 
IHC:
*CD5 +ve.<ref>{{Ref PBoD|708}}</ref>
 
==Staging==
There is a system by Masaoka et al..<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>
 
==IHC and thymus==
Types A, AB, B:<ref>CJS. January 2010.</ref>
*CK7-, CK20-, CAM5.2+, CK5/6+, p63+, CD5-.
 
Type C:<ref>CJS. January 2010.</ref>
*CD5+.
 
All types:<ref>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.
 
Others (immature T cells):
*TdT.
*CD99.
 
==Anterior mediastinum mass DDx==
4 Ts (mnemonic):
*Thymoma.
*Terrible [[lymphoma]].
*[[Teratoma]].
*[[Thyroid]] (ectopic).


==See also==
=See also=
*[[Thyroid gland]].
*[[Thyroid gland]].
*[[Basics]].
*[[Basics]].
*[[Lung]].
*[[Lung]].


==References==
=References=
{{reflist|2}}
{{reflist|2}}


[[Category:Haematopathology]]
[[Category:Haematopathology]]
Michael
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