PMC6629999_01
Axial section of thoracic computed tomography showing anterior mediastinal mass.
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Review of the thoracic imaging showed a 45 x 26 x 34 mm mediastinal mass with extension to the pulmonary trunk but without evidence of pericardial invasion ( Fig. 1 ).
Thymectomy specimen showing a measuring 124 x 110 x 25 mm lobulated cream surface without a discrete mass.
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 At macroscopic examination the removed thymus was lobulated and firm, measuring 124 x 110 x 25 mm ( Fig. 2 ) with a weight of 87 g (expected normal weight for age 21.6 +- 19.0 g  ).
(
A
) Low-power view of thymectomy specimen showing ordered expansion of the cortical and medullary thymic compartments in keeping with "true" hyperplasia. (
B
) Focal secondary lymphoid follicles in keeping with "lymphoid" hyperplasia.
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Following extensive sampling, histopathological examination revealed expanded thymic tissue consistent with "true" thymic hyperplasia ( Fig. 3A ) with a minor component of "lymphoid" hyperplasia ( Fig. 3B ).