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]

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 of adaptive immunity.

Pathogenesis

• The exact pathogenesis of the primary tumor development is not well 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 associated autoimmune disorders.

Microscopic Pathology

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

Gross Pathology

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

Genetic Features

Genetic alterations reported for the different WHO histological thymomasubtypes

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

Video

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Associated Disorders

Approximately 30% of patients have their thymomas discovered because they have an 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
Haematologic Autoimmune Diseases	Anemia: pure red cell aplasia, pernicious anemia, hemolytic anemia, aplastic anemia. Other isolated cytopenia: eosinophils,basophils, neutrophils, immunodeficiencies: hypogammaglobulinaemia +/- T-cell deficiencies (Good syndrome)
Dermatologies Diseases	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