Cystic lesions

Thymic cyst

Topic Completed: 1 December 2012

Minor changes: 20 February 2020

Copyright: 2003-2018,, Inc.

PubMed Search: Thymic cyst[TI] mediastinum

Hanni Gulwani, M.B.B.S.
Page views in 2020: 5,618
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Cite this page: Gulwani H. Thymic cyst. website. Accessed December 6th, 2021.
Definition / general
  • Thymus derived from third and fourth branchial pouch, as is parathyroid gland
  • Usually presents as incidental mass in anterosuperior mediastinum
  • Congenital (unilocular) or acquired (multilocular)
  • Rarely occur postoperatively
  • Mixed multilocular thymic cyst: has parathyroid or salivary gland tissue
  • Usually ages 20 - 50 years
Clinical features
Radiology description
  • Xray: rounded, circumscribed masses in anterior mediastinum, may have peripheral rim of calcification
Case reports
Gross description
  • Up to 18 cm
  • Unilocular with thin wall and serous fluid or multilocular with turbid, cheesy or hemorrhagic material, thick wall and fibrous adhesions
  • Either centered in thymus or connected to it by a small pedicle
Gross images

Case of the Week #333:

Images hosted on other servers:

Thin walled cyst with thyroid

Microscopic (histologic) description
Unilocular cysts:
  • Have thin wall with a few layers of bland squamoid cells and thymic tissue in wall, no inflammation, no cholesterol granulomas, no hemorrhage

Multilocular cysts:
  • May have more layers of squamoid, cuboidal, columnar, micropapillary or mixed glandular epithelium
  • May have pseudoepitheliomatous hyperplasia
  • Usually cholesterol granulomas
  • Commonly lymphocytes, granulation tissue, hemorrhage
  • Cysts separated by thick fibrous septae
  • 50% have Hassall corpuscles or other thymic tissue but not in cyst wall
  • No cartilage or smooth muscle is present
Microscopic (histologic) images

Case of the Week #333:

Various images

Images hosted on other servers:

Bland squamoid epithelium

Papillary outpouchings

Cholesterol clefts

Thymic tissue in cyst wall

Squamous epithelial lining

Proliferating multilocular thymic cyst
Definition / general
  • Resembles cutaneous proliferating epidermoid cyst and proliferating trichilemmal cyst

Microscopic (histologic) description
  • Pseudoepitheliomatous hyperplasia of cyst lining cells (narrow tongues of squamoid epithelium extending deeply into fibrous cyst wall) with reactive changes but no dysplasia
  • Typical mitotic figures present

Differential diagnosis
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