Thyroid & parathyroid

Other thyroid nonneoplastic


Topic Completed: 1 August 2017

Minor changes: 3 June 2021

Copyright: 2003-2021,, Inc.

PubMed search: Crystals [title] thyroid

Andrey Bychkov, M.D., Ph.D.
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Cite this page: Bychkov A. Crystals. website. Accessed December 3rd, 2021.
Definition / general
Essential features
  • Colloid often contains calcium oxalate crystals, particularly in nodular goiter but also in aged or hypoactive benign thyroid and rarely in tumors
  • Appear as intracolloidal birefringent crystals of various shape incidentally found in histologic sections or fine needle aspirates
  • Calcium oxalate crystals are useful in differentiating thyroid tissue from parathyroid tissue (no crystals) at frozen section
  • No association with abnormal laboratory findings of thyroid function
  • Patients with renal failure on dialysis may have disseminated oxalate deposition in visceral organs including thyroid
Prognostic factors
  • No prognostic implications
Case reports
Microscopic (histologic) description
  • Anisotropic crystals appear as small transparent pale or colorless refractile foci variable in size and shape (polygonal, sand-like, needle shaped, rhomboid or irregular)
  • Large round or oval vacuoles within the colloid may contain calcium oxalate crystals
  • Crystals are strongly birefringent under polarized light microscopy
  • Intrathyroidal crystals are exclusively found within colloid and do not appear within cytoplasm of the follicular epithelial cells or in stroma (Wenig: Atlas of Head and Neck Pathology, Third Edition, 2015)
  • Background thyroid (Am J Surg Pathol 1993;17:698):
    • There is no association with any specific thyroid condition
    • Highest prevalence of crystals was found in nodular goiters and follicular adenomas (up to 80%)
    • Rarely associated with malignant tumors, 33% prevalence in follicular carcinoma and 5% in papillary carcinoma
    • One study found low prevalence in Graves' disease and Hashimoto thyroiditis but a large amount of crystals in subacute thyroiditis, which were also located in granulomas (Mills: Histology for Pathologists, Fourth Edition, 2012)
  • Crystals found at autopsy tend to disappear within hours after death (Virchows Arch A Pathol Anat Histopathol 1993;422:301)
Microscopic (histologic) images

Contributed by Andrey Bychkov, M.D., Ph.D.

Abundant calcium oxalate crystals

Follicular adenoma: calcium oxalate crystals

Calcium oxalate crystals in the colloid

AFIP images

Calcium oxalate crystals

Cytology description
  • Variably sized and shaped crystals in the background of colloid (Diagn Cytopathol 2016;44:814)
  • In one series, total incidence of birefringent crystals was 45%, including 68% in benign lesions and 21% in malignant tumors (Acta Cytol 1999;43:575)
  • Benign diseases show a more scattered distribution of birefringent crystals, compared to the typical focal distribution in cancer
  • Occurrence of crystals in thyroid FNAC is lower than that in histologic specimens
Electron microscopy images

Images hosted on other servers:

Calcium oxalate crystallite

Spherical apatite crystallites

Differential diagnosis
  • Intracolloidal vacuoles (empty spaces) and dense particulated colloid (basophilic clumps) do not show birefringence under polarized light
Additional references
Board review style question #1
How are calcium oxalate crystals useful in frozen sections from thyroid and parathyroid?

  1. Differentiate cancer from benign tissue
  2. Distinguishing thyroid from parathyroid tissue
  3. Helps to locate psammoma bodies
  4. Identify age of patient
  5. No practical utility
Board review style answer #1
B. Distinguishing thyroid from parathyroid tissue. Calcium oxalate crystals are useful in differentiating thyroid tissue (scattered to abundant crystals) from parathyroid tissue (no crystals) at frozen section.

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Reference: Crystals
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