Mediastinum
Cystic lesions
Thymic cyst

Author: Hanni Gulwani, M.D. (see Authors page)

Revised: 15 June 2018, last major update December 2012

Copyright: (c) 2003-2018, PathologyOutlines.com, Inc.

PubMed Search: Thymic cyst[TI] mediastinum

Cite this page: Gulwani, H. Thymic cyst. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/mediastinumthymiccyst.html. Accessed September 25th, 2018.
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
Epidemiology
  • 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

Images hosted on PathOut server:

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

Images hosted on PathOut server:

Case of the Week #333:



Various images



Images hosted on other servers:

Flat epithelial lining

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