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

Pathophysiology

Microscopic Pathology

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

Histopathological image of Thymoma type B1. Anterior mediastinal mass surgically resected. Hematoxylin & eosin stain.

Histopathological image representing a noninvasive Thymoma type B1, surgically resected. Hematoxylin & eosin.

Histopathological image of Thymoma type B1. Anterior mediastinal mass surgically resected. Cytokeratin CAM5.2 immunostain.

Micrograph of a Thymoma. FNA specimen. Field stain.

Gross Pathology

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

Mediastinum: locally invasive, circumscribed Thymoma. Its cut surface bulges, and is pale tan and faintly lobulated. It invaded the capsule at a few points but still remained within the thymus.

Genetic Features

Genetic alterations reported for the different WHO histological thymoma subtypes

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

Associated Disorders

A third of the patients who have a thymoma detected because they have an associated autoimmune disorder. The most common condition in this group is myasthenia gravis (of which 25-50% are associated with a thymoma); patients with myasthenia are routinely screened for thymoma. Other associated autoimmune conditions are pure red cell aplasia and Good's syndrome (thymoma with combined immunodeficiency and hypoimmunoglobulinemia G). Rare associations that have been reported are: acute pericarditis, Addison's disease, agranulocytosis, alopecia areata, ulcerative colitis, Cushing's disease, hemolytic anemia, limbic encephalopathy, myocarditis, nephrotic syndrome, panhypopituitarism, pernicious anemia, polymyositis, rheumatoid arthritis, sarcoidosis, scleroderma, sensorimotor radiculopathy, stiff person syndrome, systemic lupus erythematosus and thyroiditis.