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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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==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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==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.
*Epithelial cells.
**Spindle cells - Type A.
**Epithelioid cells - Type B.
 
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>
 
===IHC===
*[[p63]] +ve.<ref name=pmid24923897>{{cite journal |author=Adam P, Hakroush S, Hofmann I, Reidenbach S, Marx A, Ströbel P |title=Thymoma with loss of keratin expression (and giant cells): a potential diagnostic pitfall |journal=Virchows Arch. |volume= |issue= |pages= |year=2014 |month=June |pmid=24923897 |doi=10.1007/s00428-014-1606-6 |url=}}</ref>
*TdT +ve.


==Metaplastic thymoma==
==Metaplastic thymoma==
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==Thymic carcinoma==
==Thymic carcinoma==
*Previously ''Thymic tumour type C''.
{{Main|Thymic carcinoma}}
===General===
*Rare.
*Usually arise ''de novo'', i.e. thymoma is not generally a precursor.
*Risk factors - possibly: [[smoking]], radiation.<ref name=pmid23319214/>
 
===Microscopic===
Features:<ref name=Ref_WMSP147>{{Ref WMSP|147}}</ref>
*Cytologically malignant - variable morphology.
**[[Squamous cell carcinoma]] is the most common (65-73% of cases<ref name=pmid23319214>{{Cite journal  | last1 = Thomas de Montpréville | first1 = V. | last2 = Ghigna | first2 = MR. | last3 = Lacroix | first3 = L. | last4 = Besse | first4 = B. | last5 = Broet | first5 = P. | last6 = Dartevelle | first6 = P. | last7 = Fadel | first7 = E. | last8 = Dorfmuller | first8 = P. | title = Thymic carcinomas: clinicopathologic study of 37 cases from a single institution. | journal = Virchows Arch | volume = 462 | issue = 3 | pages = 307-13 | month = Mar | year = 2013 | doi = 10.1007/s00428-013-1371-y | PMID = 23319214 }}</ref><ref name=pmid23866799>{{Cite journal  | last1 = Zhao | first1 = Y. | last2 = Zhao | first2 = H. | last3 = Hu | first3 = D. | last4 = Fan | first4 = L. | last5 = Shi | first5 = J. | last6 = Fang | first6 = W. | title = Surgical treatment and prognosis of thymic squamous cell carcinoma: a retrospective analysis of 105 cases. | journal = Ann Thorac Surg | volume = 96 | issue = 3 | pages = 1019-24 | month = Sep | year = 2013 | doi = 10.1016/j.athoracsur.2013.04.078 | PMID = 23866799 }}</ref>).
*+/-Squamous differentiation.
 
Notes:
*Staging depends on capsular invasion.
 
DDx:
*[[Thymoma]].
*[[Lung cancer|Lung carcinoma]].
*[[Gastrointestinal stromal tumour]].<ref name=pmid23375402>{{Cite journal  | last1 = Rossi | first1 = V. | last2 = Donini | first2 = M. | last3 = Sergio | first3 = P. | last4 = Passalacqua | first4 = R. | last5 = Rossi | first5 = G. | last6 = Buti | first6 = S. | title = When a thymic carcinoma becomes a GIST. | journal = Lung Cancer | volume = 80 | issue = 1 | pages = 106-8 | month = Apr | year = 2013 | doi = 10.1016/j.lungcan.2013.01.003 | PMID = 23375402 }}</ref>
 
====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 (90% of cases<ref name=pmid23319214/>).<ref name=Ref_PBoD708>{{Ref PBoD|708}}</ref>
*CD117 +ve (87% of cases<ref name=pmid23319214/>).
*CD7 +ve.
*[[TTF-1]] -ve.
 
Note:
*Should stain with keratins.


=See also=
=See also=
Michael
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