Microscopic thymoma

Definition

Microscopic multifocal epithelial proliferation within the thymus without a gross tumour, usually in the context of myasthenia gravis. It is unclear whether these foci are a precursor to a macroscopic thymoma.

Epidemiology

Such foci occur in 4% of control thymuses0.

Clinical features

Such foci are commonly found in association with myasthenia gravis in the presence or absence of a gross tumour.

Macroscopic appearances

There is no macroscopic tumour.

Histopathology

The epithelial cells vary in appearance, from bland to pleomorphic, spindle cell to polygonal. Intraepithelial T-cells are usually absent.

References

0 Tumours of the Lung, Pleura, Thymus and Heart. WHO Classification of Tumours. IARC Press 2004.

This page last revised 4.1.2006.

©SMUHT/PW Bishop