Thyroid cytology

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Author: Mikael Häggström [note 1]


A minimum number of 6 clusters with 10 cells each has been arbitrary established to assume adequacy for a definitive diagnosis.[1] The presence of characteristic cells may still confer a definitive diagnosis, but otherwise, the report will simply state inadequate number of cells.

Risk stratification

Classify findings as per the Bethesda system:

Bethesda system
Category Description[2] Example report
I Non diagnostic/unsatisfactory
II Benign (colloid and follicular cells) Thyroid aspiration, right upper pole:
Negative for malignant cells.
Clusters of benign follicular epithelial cells and colloid. Findings are consistent with a benign hyperplastic nodule. (Bethesda category II)
III Atypia of undetermined significance (AUS) or follicular lesion of undetermined significance (FLUS) (follicular or lymphoid cells with atypical features) Thyroid aspiration, right mid pole:
Clusters of atypical follicular cells of undetermined significance (Bethesda category III).
IV Follicular nodule/suspicious follicular nodule (cell crowding, micro follicles, dispersed isolated cells, scant colloid)
V Suspicious for malignancy
VI Malignant
Papillary thyroid carcinoma, with typical features shown. Pap stain. However, cytology cannot distinguish Hürthle cell adenoma from Hürthle cell carcinoma, which requires histopathologic sections to see transcapsular or vascular invasion. Hürthle cell hyperplasia (as seen in Hashimoto's thyroiditis) may show moderate variation in nuclear sizes and prominent nucleoli, but further findings favoring Hürthle cell neoplasm include a large number of Hürthle cells, and discohesiveness.


  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.

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  1. Michael, Claire W.; Pang, Yijun; Pu, Robert T.; Hasteh, Farnaz; Griffith, Kent A. (2007). "Cellular adequacy for thyroid aspirates prepared by ThinPrep: How many cells are needed? ". Diagnostic Cytopathology 35 (12): 792–797. doi:10.1002/dc.20768. ISSN 87551039. 
  2. "The bethesda system for reporting thyroid cytopathology: interpretation and guidelines in surgical treatment ". Indian Journal of Otolaryngology and Head and Neck Surgery 64 (4): 305–311. December 2012. doi:10.1007/s12070-011-0289-4. PMID 24294568. 
  3. Image by Mikael Häggström, MD. References for findings:
    - Ayana Suzuki, C.T., Andrey Bychkov, M.D., Ph.D.. Hürthle cell neoplasm. Pathology Outlines. Last author update: 7 May 2020. Last staff update: 12 May 2022
    - Shawky M, Sakr M (2016). "Hurthle Cell Lesion: Controversies, Challenges, and Debates. ". Indian J Surg 78 (1): 41-8. doi:10.1007/s12262-015-1381-x. PMID 27186039. PMC: 4848220. Archived from the original. . 

Image sources