Difference between revisions of "Thymus"

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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>PBoD P.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===
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>
*No germinal centres.
*No germinal centres.
*Hassall's corpusle (thymic corpusle).
*Hassall's corpusle (thymic corpusle).
**Round eosinophilic thingy.
**Round eosinophilic thingy.
**Thought to arise from medullary epithelial cells (see ''cell types'').<ref>PBoD P.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===
Cells of the thymus (short version):
Cells of the thymus (short version):
#Cortical epithelial cells.<ref>PBoD P.706.</ref>
#Cortical epithelial cells.<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>
#*Epithelioid.
#*Epithelioid.
#*Abundant cytoplasm.
#*Abundant cytoplasm.
#*Pale nuclei with small nucleoli.
#*Pale nuclei with small nucleoli.
#Medullary epithelial cells.<ref>PBoD P.706.</ref>
#Medullary epithelial cells.<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>
#*Spindle morphology.
#*Spindle morphology.
#*Scant cytoplasm.
#*Scant cytoplasm.
Line 32: Line 47:
*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>


==Thymic follicular hyperplasia==
==IHC and thymus==
*AKA ''thymic follicular hyperplasia''.
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.


Features:<ref>PBoD P.707.</ref>
Type C:
*Follicular centres in the thymus.
*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>


Associations:<ref>PBoD P.707-8.</ref>
All types:<ref name=cjs>CJS. January 2010.</ref>
*Myasthenia gravis.
*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.
*Graves' diseases.
*SLE.
*Rheumatoid arthritis.
*Other autoimmune diseases.


==Tumours of the thymus (overview)==
Others (immature T cells):
Thymic tumours are derived from the epithelial component of the thymus, i.e. the ''cortical epithelial cells'' and ''medullary epithelial cells''.
*TdT +ve.
*CD99 +ve.


The ''WHO'' published a widely used system - WHO classification:<ref>Sternberg's DSP. 4th Ed. P.1264.</ref>
==Anterior mediastinum mass DDx==
===Type A===
{{Main|Mediastinum}}
*AKA ''Spindle cell'' or ''medullary''.
4 Ts (mnemonic):
*Arise from ''medullary epithelial cells''.
*Thymoma.
*Good prognosis.
*Terrible [[lymphoma]].
*[[Teratoma]].
*[[Thyroid]] (ectopic).


IHC:
==Thymus and stress==
*Usu. keratin+.
*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>
===Type AB===
*Like Type A... but with foci of lymphocytes.
===Type B1===
*Near normal, expanded cortex.


Lesion consists of:
=Specific conditions=
*>2/3 lymphocytes, <1/3 cortical epithelial cells.
==Thymic follicular hyperplasia==
===Type B2===
*AKA ''thymic follicular hyperplasia''.
*Neoplastic cells with some resemblance to cortical epithelial cells.
**Epithelioid cells with distinct nucleoli.
**May be perivascular.
*Large population of lymphocytes.


Lesion consists of:
Features:<ref name=Ref_PBoD707-8>{{Ref PBoD|707-8}}</ref>
*<2/3 but >1/3 lymphocytes, >1/3 but <2/3 cortical epithelial cells.
*Follicular centres in the thymus.


Notes:
Associations:<ref name=Ref_PBoD707-8>{{Ref PBoD|707-8}}</ref> 
*Most common '''B''' type.
*Myasthenia gravis.
===Type B3===
*[[Graves' disease]].
*Neoplastic cells with some resemblance to cortical epithelial cells.
*[[Systemic lupus erythematosus]] (SLE).
**Polygonal/round shape.
*[[Rheumatoid arthritis]].
**Form sheets (of cells) - '''key feature'''.
*Other [[autoimmune diseases]].
*Lymphocytes - less than in Type B2.
*AKA ''well-differentiated thymic carcinoma''.


Lesion consists of:
==Thymoma==
*<1/3 lymphocytes, >2/3 cortical epithelial cells.
{{Main|Thymoma}}
===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:
==Metaplastic thymoma==
*Type B1:
*[[AKA]] ''thymoma with pseudosarcomatous stroma''.<ref name=metapl_thy/>
**[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==
===General===
*AKA ''Thymic tumour type C''.  
*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>
*Two reports of transformation into [[thymic carcinoma]].<ref name=pmid20034984/>


IHC:  
===Microscopic===
*CD5 +ve.<ref>PBoD P.708.</ref>
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>
#Epithelioid cells.
#Spindle cells.
*Few lymphocytes.


==Staging==
DDx:
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>
*[[Thymic carcinoma]] with sarcomatoid differentiation.


==IHC and thymus==
====Images====
Types A, AB, B:<ref>CJS. January 2010.</ref>
www:
*CK7-, CK20-, CAM5.2+, CK5/6+, p63+, CD5-.
*[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>


Type C:<ref>CJS. January 2010.</ref>
===IHC===
*CD5+.
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>


All types:<ref>CJS. January 2010.</ref>
==Thymic carcinoma==
*CD1a (immature T cells), Lnagerhans cell, dendritic cells, CEA+ (focal), vimentin-.
{{Main|Thymic carcinoma}}
==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]]

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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