Cystic lesions

Thymic cyst

Last author update: 1 December 2012
Last staff update: 19 September 2023

Copyright: 2003-2023,, Inc.

PubMed Search: Thymic cyst mediastinum

Hanni Gulwani, M.B.B.S.
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Cite this page: Gulwani H. Thymic cyst. website. Accessed September 21st, 2023.
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
  • ≤ 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 #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 #333

Various images

Images hosted on other servers:

Bland squamoid epithelium

Papillary outpouchings

Cholesterol clefts

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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