Ectopic hamartomatous thymoma, spindle cell thymic anlage tumour

Definition

This tumour probably arises from the branchial anlage. It is probably NOT a tumour of thymic origin.

Epidemiology

This is a rare tumour of adults. There is a very large male predominance.

Clinical features

The tumour involves the neck or chest wall. They are slow growing.

Macroscopic appearances

The tumours form a solitary well circumscribed mass. They are of rubbery consistency. The cut surface is grey-white to tan. In many case, there is cyst formation.

Histopathology

The tumours are composed of a mix of spindle and epithelial cells. The spindle cells are an admixture of plump and delicate cells. The epithelial component may show squamous, glandular or clear cell differentiation. Mature adipose tissue is present in varying proportions. Smooth muscle may be present focally. Psammomatous microcalcification may occur. Mitotic rates are up to 7 per 50 HPF.

Immunohistochemistry

 key: +: <1% of cells, ++: 1 to 25 % of cells, +++: 26-50% of cells, ++++: >50% of cells

Differential diagnosis

• mixed tumours of skin adnexa: ectopic hamartomatous thymoma lacks chondroid or cartilaginous foci.

• mixed salivary gland tumour: ectopic hamartomatous thymoma lacks chondroid or cartilaginous foci.

• sarcomatous carcinoma: shows cytological atypia

• synovial sarcoma: the origin is deep seated

• peripheral nerve sheath tumour: positive for S-100

• cystic teratoma: the origin is deep seated

• spindle cell lipoma

Prognosis

Local recurrence may occur if the tumour is incompletely excised.

References

Fetsch, J. F., W. B. Laskin, et al. (2004). "Ectopic hamartomatous thymoma: a clinicopathologic and immunohistochemical analysis of 21 cases with data supporting reclassification as a branchial anlage mixed tumor." Am J Surg Pathol 28(10): 1360-70.

This page last revised 14.11.2004.

©SMUHT/PW Bishop