True thymic hyperplasia

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True thymic hyperplasia is a form of thymic hyperplasia where there is enlargement of the thymus but with its normal structure being retained.

Pathology

The underlying pathogenesis of true thymic hyperplasia is largely unknown.

There is an increase of both size and weight of the gland but with normal microscopic architecture being maintained.

It can occurs in three different clinicopathologic forms

  • true thymic hyperplasia without any other disease: extremely rare and only seven well documented examples could be found in a review of the literature.
  • thymic rebound hyperplasia: enlargement of the thymus gland is reported as a form of "rebound phenomenon" in a number of conditions such as
    • recovery from severe stress situations
    • after administration of steroids
    • treatment of malignant tumors: chmotheraphy
  • thymic hyperplasia in association with endocrine abnormalities e.g. sarcoidosis, Beckwith-Wiedemann syndrome, hyperthyroidism

See also