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thymoma type B3

Wednesday 29 May 2013


- Type B3 thymoma at Webpathology

Type B3 thymoma accounts for between 10-25% of all thymomas and are frequently associated with myasthenia gravis.

Type B3 thymoma is composed of medium-sized round or polygonal cells arranged in clusters and sheets separated by thick fibrous septa. The tumor cells may exhibit mild cytologic atypia. They are admixed with a small component of lymphocytes.

Mild cytologic atypia and scant numbers of intraepithelial lymphocytes can be better appreciated in a high power view of a type B3 thymoma.

The tumor cells are polygonal with distinct cell borders and clear or eosinophilic cytoplasm.

Type B3 thymomas may show spindling of tumor cells.

The tumor can be widely invasive and infiltrated into the mediastinal fat – a feature commonly observed in type B3 thymomas. The paucity of lymphocytes is a diagnostic feature.

Polygonal or spindle tumor cells are arranged in sheets. Only rare lymphocytes are seen.

The tumor cells are arranged in solid sheets and show rare lymphocytes.

Type B3 thymoma are usually invasive at presentation, often unresectable, and show recurrences and metastases in 15% and 20% of cases respectively.

An extensive squamoid differentiation. Such thymomas are often referred to as squamoid thymomas. Type B3 thymoma can show a squamoid morule surrounded by polygonal tumor cells and scant lymphocytes.

Steroid treatment in thymoma patients presenting with myasthenia gravis may produce a sponge-like appearance with formation of microcysts containing foamy histiocytes.

See also

- thymomas type B

  • thymoma type B1
  • thymoma type B2