Thyroid gland
Other carcinoma

Authors: Shuanzeng Wei, M.D., Ph.D., Zubair W. Baloch M.D., Ph.D. (see Authors page)

Revised: 16 February 2017, last major update June 2016

Copyright: (c) 2003-2017,, Inc.

PubMed search: CASTLE thyroid
Cite this page: CASTLE. website. Accessed February 19th, 2018.
Definition / general
  • CArcinoma Showing Thymus-Like differentiation
  • Terminology first used in 1991 (Hum Pathol 1991;22:349)
  • Also known as intrathyroidal (ectopic) thymic carcinoma
Essential features
  • Intrathyroidal (ectopic) thymic carcinoma located at the lower pole of thyroid
  • Also called intrathyroidal thymoma (not commonly used as it confuses as benign)
  • Mean age 48.5 years
  • Commonly involves the lower pole of the thyroid and surrounding soft tissue
Radiology description
  • Nodular masses located in the lower neck between the inferior pole of the thyroid and the upper mediastinum (Br J Radiol 2016;89:20150726)
Prognostic factors
  • Good prognosis, with 5 year and 10 year survival of 90% and 82%; poorer prognosis if nodal metastases or tumor extension to surrounding tissue (Am J Clin Pathol 2007;127:230)
Case reports
  • Total thyroidectomy with neck dissection and radiation
Gross description
  • Well defined, lobulated white / tan mass
Gross images

Images hosted on other servers:

Lobulated, solid and tan colored (fig. 3A)

Microscopic (histologic) description
  • Lobular with fibrous bands separating solid islands of squamoid cells with variable lymphocytes (mixed mature T and B cells vs immature B cells in thymoma)
  • Tumor cells either have ill defined cell border with vesicular nuclei and prominent nucleoli, or show squamous differentiation with distinct cell borders
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Dr. Shuanzeng Wei and Dr. Zubair W. Baloch, University of Pennsylvania (USA):

Well demarcated tumor nests

Tumor nest

Tumor cells with indistinct cell border

AFIP Images:

Irregularly shaped lobules in solid pattern

Sharply defined tumor lobule

Plump epithelial cells and small lymphocytes

Images hosted on other servers:

Various images

Cytology description
Cytology images

Images hosted on other servers:

Various images (fig. 2)

Dyscohesivepolygonal to ovoid malignant cells (fig. 1)

Positive stains
Negative stains
Differential diagnosis