Thymoma pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Amr Marawan, M.D. [2] Ahmad Al Maradni, M.D. [3]Sabawoon Mirwais, M.B.B.S, M.D.[4]

Overview

On gross pathology, a well-circumscribed mass, that is locally invasive, is a characteristic finding of thymoma. On microscopic histopathological analysis, round cells with ample vacuolated cytoplasms and fat droplets are characteristic findings of thymoma.

Pathophysiology

Physiology

• Thymus is the site of maturation of T cells.
• This makes thymus the primary center responsible for adaptive immunity.

Pathogenesis

• The exact pathogenesis of the primary tumor development is not completely understood.

• Primary tumors of thymus are relatively rare.
• Thymoma is the most common type of primary tumor of thymus.
• Thymoma is histologically comprised of abnormally conditioned T cells.
• The mingling of these abnormal T cells into the circulation is believed to be involved in the causality of the associated autoimmune disorders.

Genetics

Genetic Alterations Reported for the Different WHO Histological Thymoma sub-types

WHO Type	Chromosomal Gains	Chromosomal Losses
Type A	None	-6p
Type AB	None	-5q21 - 22 -6q -12p -16q
Type B3	+1q	-6 -13q

Associated Conditions

Approximately 30% of the patients have their thymomas discovered because of a symptomatic associated autoimmune disorder. These disorders include:

Type	Diseases
Neuromuscular diseases	Myasthenia gravis Neuromyotonia Rippling muscle disease Polymyositis/dermatomyositis Encephalitis (limbic, cortical and brain stem) Intestinal pseudoobstruction
Hematologic autoimmune diseases	Anemia: Pure red cell aplasia, pernicious anemia, hemolytic anemia, aplastic anemia. Other isolated cytopenia: Eosinophils, basophils, neutrophils Immunodeficiencies: Hypogammaglobulinaemia, Good syndrome
Dermatologic disorders	Pemphigus (foliaceus or paraneoplastic) Lichen planus Alopecia areata
Endocrine disorders	Addison disease Graves disease Cushing's disease
Renal and hepatic diseases	Glomerulonephritis Autoimmune hepatitis
Systemic autoimmune diseases	SLE Sjögren's syndrome Systemic sclerosis Graft-versus-host disease

Gross Pathology

On gross pathology, a well circumscribed mass, that is locally invasive, is a characteristic finding of thymoma.

Microscopic Pathology

On microscopic histopathological analysis, round cells, with ample vacuolated cytoplasms, and fat droplets are characteristic findings of thymoma.

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