Difference between revisions of "Thymus"

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'''Thymus''' is an annoying little organ that is in the mediastinum.
'''Thymus''' is an annoying little organ that is in the mediastinum.


==General==
=Overview=
*Involutes after childhood.
*Thymus involutes after childhood.
*Location: anterior mediastinum.
*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>
*May contain within it parathyroid.<ref name=Ref_PBoD706>{{Ref PBoD|706}}</ref>


==Histology==
 
 
==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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*Other WBCs: B lymphocytes, neutrophils, eosinophils.
*Other WBCs: B lymphocytes, neutrophils, eosinophils.
*Myoid cells.
*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:
Images:
*[http://commons.wikimedia.org/wiki/File:Thymic_corpuscle.jpg Thymic corpusle (wikimedia.org)].
*[http://commons.wikimedia.org/wiki/File:Thymic_corpuscle.jpg Thymic corpusle (wikimedia.org)].


==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==
{{Main|Mediastinum}}
4 Ts (mnemonic):
*Thymoma.
*Terrible [[lymphoma]].
*[[Teratoma]].
*[[Thyroid]] (ectopic).
=Absence of the thymus=
==Di George syndrome==
==Di George syndrome==
*Things go wrong with the thymus... very wrong.
*Things go wrong with the thymus... very wrong.


==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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*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''.
===General===
*Strong association with autoimmune disease, esp. myasthenia gravis.


====Classification====
The ''WHO'' published a widely used system - WHO classification:<ref>{{Ref Sternberg4|1264}}</ref>
The ''WHO'' published a widely used system - WHO classification:<ref>{{Ref Sternberg4|1264}}</ref>
===Type A===
=====Type A=====
*AKA ''Spindle cell'' or ''medullary''.
*AKA ''Spindle cell'' or ''medullary''.
*Arise from ''medullary epithelial cells''.
*Arise from ''medullary epithelial cells''.
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IHC:
IHC:
*Usu. keratin+.
*Usu. keratin+.
===Type AB===
=====Type AB=====
*Like Type A... but with foci of lymphocytes.
*Like Type A... but with foci of lymphocytes.
===Type B1===
=====Type B1=====
*Near normal, expanded cortex.
*Near normal, expanded cortex.


Lesion consists of:
Lesion consists of:
*>2/3 lymphocytes, <1/3 cortical epithelial cells.
*>2/3 lymphocytes, <1/3 cortical epithelial cells.
===Type B2===
=====Type B2=====
*Neoplastic cells with some resemblance to cortical epithelial cells.
*Neoplastic cells with some resemblance to cortical epithelial cells.
**Epithelioid cells with distinct nucleoli.
**Epithelioid cells with distinct nucleoli.
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Notes:
Notes:
*Most common '''B''' type.
*Most common '''B''' type.
===Type B3===
=====Type B3=====
*Neoplastic cells with some resemblance to cortical epithelial cells.
*Neoplastic cells with some resemblance to cortical epithelial cells.
**Polygonal/round shape.
**Polygonal/round shape.
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Lesion consists of:
Lesion consists of:
*<1/3 lymphocytes, >2/3 cortical epithelial cells.
*<1/3 lymphocytes, >2/3 cortical epithelial cells.
===Type C===
 
*AKA ''thymic carcinoma''.
Note:
*Neoplastic cells with some resemblance to cortical epithelial cells - with cytologic features of malignancy.
*Neoplastic cells derived from the thymus with cytologic features of malignancy are [[thymic carcinoma]]s.
**Any nuclear atypia of epithelial thymocytes... puts a tumour into this group.


Images:
Images:
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**[http://commons.wikimedia.org/wiki/File:Thymoma_B1_(2).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)].
**[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)].
==Thymoma==
===General===
*Strong association with autoimmune disease, esp. myasthenia gravis.


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


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


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

Revision as of 22:09, 10 December 2011

Thymus is an annoying little organ that is in the mediastinum.

Overview

  • Thymus involutes after childhood.
  • Location: anterior mediastinum.
  • Important for development of the immune system.
  • May contain within it parathyroid.[1]


Normal histology

General

Features:[2]

  • No germinal centres.
  • Hassall's corpusle (thymic corpusle).
    • Round eosinophilic thingy.
    • Thought to arise from medullary epithelial cells (see cell types).[1]

Cell types

Cells of the thymus (short version):

  1. Cortical epithelial cells.[1]
    • Epithelioid.
    • Abundant cytoplasm.
    • Pale nuclei with small nucleoli.
  2. Medullary epithelial cells.[1]
    • 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:

IHC and thymus

Types A, AB, B:[3]

  • CK7-, CK20-, CAM5.2+, CK5/6+, p63+, CD5-.

Type C:[4]

  • CD5+.

All types:[5]

  • CD1a (immature T cells, Langerhans cells, dendritic cells[6]), CEA +ve (focal), vimentin -ve.

Others (immature T cells):

  • TdT.
  • CD99.

Anterior mediastinum mass DDx

Main article: Mediastinum

4 Ts (mnemonic):

Absence of the thymus

Di George syndrome

  • Things go wrong with the thymus... very wrong.

Thymus and stress

  • Stress -> increased endogenous steroid -> lymphocyte death -> increased tingible body macrophages.[7]

Specific conditions

Thymic follicular hyperplasia

  • AKA thymic follicular hyperplasia.

Features:[8]

  • Follicular centres in the thymus.

Associations:[8]

Thymoma

General

  • Strong association with autoimmune disease, esp. myasthenia gravis.

Classification

The WHO published a widely used system - WHO classification:[9]

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 carcinomas.

Images:

Microscopic

Features:

  • Lymphocytes.
  • Spindle cells.

DDx:

Images:

Thymic carcinoma

  • AKA Thymic tumour type C.

General

  • Rare.
  • Usually arise de novo, i.e. thymoma is not generally a precursor.

Microscopic

Features:[10]

  • Cytologically malignant - variable morphology.
  • +/-Squamous differentiation.

DDx:

Images:

IHC

Features:[10]

  • CD5 +ve.[11]
  • CD7+ve.
  • CD117 +ve.
  • TTF-1 -ve.

Staging

There is a system by Masaoka et al..[12]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 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.
  2. ↑ URL: http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm. Accessed on: 17 June 2010.
  3. ↑ CJS. January 2010.
  4. ↑ CJS. January 2010.
  5. ↑ CJS. January 2010.
  6. ↑ URL: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf. Accessed on: 26 August 2010.
  7. ↑ 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.
  8. ↑ 8.0 8.1 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.
  9. ↑ Mills, Stacey E; Carter, Darryl; Greenson, Joel K; Oberman, Harold A; Reuter, Victor E (2004). Sternberg's Diagnostic Surgical Pathology (4th ed.). Lippincott Williams & Wilkins. pp. 1264. ISBN 978-0781740517.
  10. ↑ 10.0 10.1 Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 147. ISBN 978-0781765275.
  11. ↑ 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. 708. ISBN 0-7216-0187-1.
  12. ↑ Masaoka, A.; Monden, Y.; Nakahara, K.; Tanioka, T. (Dec 1981). "Follow-up study of thymomas with special reference to their clinical stages.". Cancer 48 (11): 2485-92. PMID 7296496.
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