Thyroid gland
Bethesda systems for cytology
Follicular neoplasm

Topic Completed: 1 May 2014

Revised: 20 August 2019

Copyright: 2014-2018,, Inc.

PubMed Search: Bethesda guidelines follicular neoplasm

Phillip A. Williams, M.D., M.Sc.
Shahid Islam, M.D., Ph.D.
Page views in 2018: 4,544
Page views in 2019 to date: 5,285
Cite this page: Williams P, Islam S. Follicular neoplasm. website. Accessed December 14th, 2019.
Definition / general
  • Based on the 2009 Bethesda Criteria (Am J Clin Pathol 2009;132:658)
  • Triage category for excision and evaluation of capsular or vascular invasion, as these are indicators of follicular carcinoma and cannot be evaluated on cytology
  • Follicular neoplasm and suspicious for a follicular neoplasm are synonymous
  • High cellularity, with conspicuous crowding and overlap
  • Scant / absent colloid
  • Hallmark feature: predominant microfollicular or trabecular arrangement of follicular cells
  • Nuclear atypia, pleomorphism, mitoses are uncommon
  • Hürthle cell neoplasm or suspicious for Hürthle cell neoplasm:
    • Variant of follicular neoplasm
    • Use for lesions consisting exclusively (or almost) of Hürthle cells (abundant finely granular blue / gray-pink cytoplasm on Diff-Quick, green on Pap or pink on H&E; enlarged eccentric nuclei with prominent nucleoli)
    • Usually contains isolated noncohesive cells
    • 16 - 25% eventually are determined to be hyperplastic (in nodular goiter or Hashimoto thyroiditis), not neoplastic
  • Risk of malignancy is 15 - 30%
  • Surgical lobectomy to assess capsule (submit in toto) (Thyroid 2006;16:109)
Sample reports
  1. Suspicious for a follicular neoplasm
  2. Suspicious for a follicular neoplasm
    • Comment: cellular aspirate composed primarily of follicular cells exhibiting a microacinar architecture
  3. Suspicious for a follicular neoplasm, Hürthle cell type
Cytology images

Images hosted on PathOut server:

Contributed by Ayana Suzuki,
Cytotechnologist, Japan:


FN - Hürthle

Contributed by Dr. Mark R. Wick:

Follicular lesion not further specified

Images hosted on other servers:

Follicular crowding

Follicular crowding and microfollicles

Trabecular arrangement of follicular cells

Follicular neoplasm

Hürthle cells

Atypical Hürthle cells

Hürthle cell neoplasm

Differential diagnosis
  • Papillary thyroid carcinoma (PTC): microfollicles but nuclear features of PTC are present (nuclear grooves, prominent nucleoli, intranuclear cytoplasmic inclusions)
Additional references
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