Thymic hyperplasia

Last revised by Rohit Sharma on 6 Feb 2022

Citation, DOI, disclosures and article data

Citation:

Radswiki T, Sharma R, Weerakkody Y, et al. Thymic hyperplasia. Reference article, Radiopaedia.org (Accessed on 19 Apr 2024) https://doi.org/10.53347/rID-15613

DOI:

https://doi.org/10.53347/rID-15613

Permalink:

https://radiopaedia.org/articles/15613

rID:

15613

Article created:

29 Oct 2011, The Radswiki ◉

Disclosures:

At the time the article was created The Radswiki had no recorded disclosures.

View The Radswiki's current disclosures

Last revised:

6 Feb 2022, Rohit Sharma ◉

Disclosures:

At the time the article was last revised Rohit Sharma had no recorded disclosures.

View Rohit Sharma's current disclosures

Revisions:

17 times, by 9 contributors - see full revision history and disclosures

Systems:

Chest, Paediatrics, Oncology

Tags:

cases, rg_39_1_edit

Synonyms:

Hyperplasia of the thymus
Hyperplastic thymus
Lymphoid follicular thymic hyperplasia
Autoimmune thymitis

Thymic hyperplasia is a disorder whereby there is hyperplasia of the thymus.

Pathology

Thymic hyperplasia can be subdivided into two forms:

Both true thymic hyperplasia and lymphoid hyperplasia manifest as diffuse symmetric enlargement of the thymus so that it is difficult to distinguish between the two types on the basis of imaging findings alone although isolated publications have suggested lymphoid thymic hyperplasia having higher HU values (i.e. >40) compared with true thymic hyperplasia ⁸.

It is important that radiologists be able to distinguish thymic hyperplasia from neoplasm, which tends to present as a focal mass.

True thymic hyperplasia

True thymic hyperplasia associations include:

rebound hyperplasia to chemotherapy/steroids (see: thymic rebound hyperplasia)
radiation therapy
burns
other severe systemic stresses

Lymphoid hyperplasia

This is also known as lymphoid follicular thymic hyperplasia or autoimmune thymitis. Lymphoid hyperplasia associations include

Radiographic features

Diffuse symmetric enlargement of the gland is the key morphologic feature of hyperplasia (neoplasm tends to manifest as a focal mass).

MRI

Chemical shift artifact may be useful in differentiating from other tumors ^3-5:

chemical shift MRI helps differentiate thymic hyperplasia and thymus gland tumors in patients 16 years of age or older
chemical shift MRI depicts no decrease in signal intensity of thymic tumors, unlike the decreased signal intensity of thymic hyperplasia ³
- this can be formally calculated using the chemical shift ratio (CSR)

Differentiating normal from hyperplastic thymus can be difficult and guidelines for making this distinction and verifying the presence of normal thymus include ⁶:

presence of rounded soft-tissue masses 7 mm
presence of a convex contour of the thymus beyond 19 years of age
presence of soft-tissue lobulation
presence of increased thymic thickness (should be ≤1.3 cm beyond age 20 years)
presence of a diagnosis associated with thymic enlargement or hyperplasia, e.g. Graves disease

Nuclear medicine

FDG PET is often performed in patients with malignancy; however, differentiation between thymic hyperplasia and thymic involvement by malignancy is difficult because the thymus demonstrates normal physiologic uptake.