Difference between revisions of "Thymus"
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*Cytologically malignant - variable morphology. | *Cytologically malignant - variable morphology. | ||
*+/-Squamous differentiation. | *+/-Squamous differentiation. | ||
DDx: | |||
*[[Thymoma]]. | |||
*[[Lung cancer|Lung carcinoma]]. | |||
Images: | Images: | ||
Revision as of 21:57, 10 December 2011
Thymus is an annoying little organ that is in the mediastinum.
General
- Involutes after childhood.
- Location: anterior mediastinum.
- Important for development of the immune system.
- May contain within it parathyroid.[1]
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):
- Cortical epithelial cells.[1]
- Epithelioid.
- Abundant cytoplasm.
- Pale nuclei with small nucleoli.
- Medullary epithelial cells.[1]
- Spindle morphology.
- Scant cytoplasm.
- Oval dark nuclei.
- T lymphocytes.
Other cells:
- Macrophages.
- Dendritic cells.
- Other WBCs: B lymphocytes, neutrophils, eosinophils.
- Myoid cells.
Images:
Di George syndrome
- Things go wrong with the thymus... very wrong.
Thymus and stress
- Stress -> increased endogenous steroid -> lymphocyte death -> increased tingible body macrophages.[3]
Thymic follicular hyperplasia
- AKA thymic follicular hyperplasia.
Features:[4]
- Follicular centres in the thymus.
Associations:[4]
- Myasthenia gravis.
- Graves' diseases.
- Systemic lupus erythematosus (SLE).
- Rheumatoid arthritis.
- Other autoimmune diseases.
Tumours of the thymus (overview)
Thymic tumours are derived from the epithelial component of the thymus, i.e. the cortical epithelial cells and medullary epithelial cells.
The WHO published a widely used system - WHO classification:[5]
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.
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:
- Type C:
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Thymoma
General
- Strong association with autoimmune disease, esp. myasthenia gravis.
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:[6]
- Cytologically malignant - variable morphology.
- +/-Squamous differentiation.
DDx:
Images:
- Thymic carcinoma - low mag. (webpathology.com).
- Thymic carcinoma - high mag. (webpathology.com).
- Thymic carcinoma - lymphoepithelioma-like - high mag. (webpathology.com).
IHC
Features:[6]
- CD5 +ve.[7]
- CD7+ve.
- CD117 +ve.
- TTF-1 -ve.
Staging
There is a system by Masaoka et al..[8]
IHC and thymus
Types A, AB, B:[9]
- CK7-, CK20-, CAM5.2+, CK5/6+, p63+, CD5-.
Type C:[10]
- CD5+.
All types:[11]
- CD1a (immature T cells, Langerhans cells, dendritic cells[12]), CEA +ve (focal), vimentin -ve.
Others (immature T cells):
- TdT.
- CD99.
Anterior mediastinum mass DDx
4 Ts (mnemonic):
See also
References
- ↑ 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.
- ↑ URL: http://www.kumc.edu/instruction/medicine/anatomy/histoweb/lymphoid/lymph03.htm. Accessed on: 17 June 2010.
- ↑ 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.
- ↑ 4.0 4.1 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.
- ↑ 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.
- ↑ 6.0 6.1 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.
- ↑ 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.
- ↑ 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.
- ↑ CJS. January 2010.
- ↑ CJS. January 2010.
- ↑ CJS. January 2010.
- ↑ URL: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1886385/pdf/amjpathol00102-0156.pdf. Accessed on: 26 August 2010.