Thymoma
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Thymoma is a common tumour of the thymus.
General
- Strong association with autoimmune disease, esp. myasthenia gravis.
Classification
The WHO published a widely used system - WHO classification:[1]
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:
Thymoma Type B1. (WC/KGH)
Thymoma Type B1. (WC/KGH)
Thymoma Type B1 - CAM5.2. (WC/KGH)
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.JPG)
_CK_CAM5-2.JPG)
Gross
- Light brown/tan.
- Encapsulated.
Image:
Microscopic
Features:
- Lymphocytes.
- Epithelial cells.
- Spindle cells - Type A.
- Epithelioid cells - Type B.
DDx:
Images:
Staging
Main article: Thymic staging
IHC
A panel:
- TdT, CD1a, CD3, CD5, CD20, Ki-67, CD117, p63, CK5/6.
Sign out
A. Lymph Node, Station 6, Lymphadenectomy: - One benign lymph node (0/1). B. Submitted as "Anterior Mediastinal Tumour (Thymus)", Excision: - Thymoma, WHO type B2. - Modified Masaoka stage IIa. - Three benign lymph nodes (0/3). - Rim of benign thymus. - Please see synoptic report.
See also
References
- ↑ 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.
- ↑ Adam P, Hakroush S, Hofmann I, Reidenbach S, Marx A, Ströbel P (June 2014). "Thymoma with loss of keratin expression (and giant cells): a potential diagnostic pitfall". Virchows Arch.. doi:10.1007/s00428-014-1606-6. PMID 24923897.
- ↑ Viti, A.; Bertolaccini, L.; Cavallo, A.; Fortunato, M.; Bianchi, A.; Terzi, A. (Sep 2014). "18-Fluorine fluorodeoxyglucose positron emission tomography in the pretreatment evaluation of thymic epithelial neoplasms: a metabolic biopsy confirmed by Ki-67 expression.". Eur J Cardiothorac Surg 46 (3): 369-74; discussion 374. doi:10.1093/ejcts/ezu030. PMID 24585679.