Thyroid gland
Benign neoplasms
Follicular adenoma

Author: Sheren Younes, M.D. (see Authors page)

Revised: 2 November 2016, last major update November 2014

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed search: follicular adenoma [title] thyroid

Cite this page: Follicular adenoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/thyroidfollicularadenoma.html. Accessed December 3rd, 2016.
Definition / General
  • Benign tumor that shows evidence of follicular differentiation, but lacks evidence of capsular and vascular invasion and lacks papillary carcinoma nuclear features
  • Atypical adenoma: pleomorphism, cellularity, mitotic figures or necrosis, but without capsular or vascular invasion; typically considered to have benign behavior, but may be precursor of anaplastic carcinoma (Hum Pathol 2003;34:666)
Epidemiology
  • Adults, usually 20 - 50 years
  • M:F= 1:6
Clinical Features
Clinical Features / Diagnosis:
  • Presents with long standing solitary thyroid nodule
  • Almost always solitary; if multiple, diagnose as multinodular goiter with adenomatous change
  • Suster restricts diagnosis to well encapsulated, usually solitary lesions, in which the uninvolved thyroid parenchyma does not display any features of nodular hyperplasia (Arch Pathol Lab Med 2006;130:984)
Laboratory
  • Patient is usually euthyroid
Radiology Description
  • Usually "cold" nodule, may be "warm", but rarely "hot"
Case Reports
Treatment
  • Lobectomy (not enucleation)
Gross Description
  • Solitary, encapsulated, variable size (1 - 10 cm)
  • Solid, fleshy, tan to light brown
  • Bulges when fresh, compresses adjacent thyroid
  • Resembles multinodular goiter due to secondary changes of hemorrhage and cystic degeneration
Gross Images
Images hosted on PathOut server:

Contributed by Dr. Mark R. Wick



Images from AFIP:

Encapsulated, homogeneous tan cut surface

Bisected adenoma has fresh hemorrhage

Marked necrosis, hemorrhage and cystic change

Marked cystic degeneration



Images hosted on other servers:

Well circumscribed tumor


Thin capsule

Well encapsulated

Central scar

Cystic and partially necrotic tumor

Micro Description
  • Completely enveloped by thin fibrous capsule
  • Architecturally and cytologically different from surrounding gland; surrounding thyroid tissue shows signs of compression
  • Closely packed follicles, trabeculae or solid sheets
  • Patterns:
    • Normofollicular (simple)
    • Macrofollicular (colloid): large colloid filled follicles with flattened epithelium
    • Microfollicular (fetal): small follicles, may have signet ring cell features (Am J Surg Pathol 1984;8:705)
    • Trabecular / solid (embryonal): cords / trabeculae with few follicles
  • May have focal papillary pattern
  • Cuboidal to low columnar cells, pale staining with round inconspicuous nucleoli
  • Mitoses are uncommon
  • Commonly secondary changes of hemorrhage, hemosiderin deposition, sclerosis, edema, necrosis, and cystic changes
  • May have spindle cell metaplasia (Am J Clin Pathol 2002;117:199), muscular cushions (focal thickening of vessel walls) in capsule, papillary hyperplasia (Histopathology 2001;39:25), bizarre nuclei (large hyperchromatic nuclei in clusters)
  • Rarely contains mature fat (Mod Pathol 1989;2:506), signet ring cells (Acta Cytol 2004;48:87), extensive bone metaplasia (J Exp Clin Cancer Res 2001;20:443)
  • No capsular or vascular invasion after thorough sampling (at least 10 blocks), no / rare mitotic figures, no papillary nuclear features
Micro Images
Scroll to see all images.

Images hosted on PathOut server:

Courtesy of Andrey Bychkov, M.D., Ph.D.

Abundant crystals of calcium oxalate

Calcium oxalate crystals



Contributed by Dr. Mark R. Wick:

Cellular follicular adenoma

Various images



Images from AFIP:

Thin and uniform fibrous capsule

Marked fibrosis and stromal hyalinization

Marked hyaline thickening of vessel walls

Marked fibrosis, hyalinization and calcium deposition


Marked vasculari-
zation resembles
a vascular
neoplasm

Capsular vessel with smooth muscle cells

Bizarre nuclei

Large, extremely irregular nuclei


With papillary hyperplasia

With papillary hyperplasia and adipose metaplasia

Cartilaginous metaplasia (adenochondroma)


Toxic adenoma is solitary and unencapsulated

Prominent clear cell change

Squamous metaplasia

Mucin production



Patterns from AFIP:

A: solid,
B: trabecular,
C: microfollicular,
D: macrofollicular

Left: macrofollicular, right: solid pattern

Signet ring



Atypical adenomas (AFIP)

Markedly cellular with irregular growth

Well formed follicles merge with solid pattern

Spindle cells mix with round cells



Not invasion:

Fine needle induced changes resemble invasion (AFIP)



Stains:

Signet ring
follicular adenoma
is thyroglobulin+
(AFIP)

Signet ring pattern, Alcian blue+



Images hosted on other servers:

Bizarre nuclei

Adjacent atrophic follicular epithelium


Clear cell adenoma



Flickr images:

Trabecular type



Patterns:

Macrofollicular

Microfollicular
with sharp circum-
scription by delicate
fibrous capsule


Microfollicular


Microfollicular

Microfollicles have
regular nuclei and
interfollicular edema


Encapsulated microfollicular adenoma

Microfollicular, trabecular and solid

Insular


Spindle cell type

Virtual Slides
Images hosted on other servers:

Follicular adenoma of the thyroid

Cytology Description
  • High cellularity, syncytial 3 dimensional arrangement, prominent nuclear crowding but no papillary nuclear features, minimal colloid
  • Cannot rule out carcinoma based on cytologic findings
  • Not all small groups of follicular cells are consistently classified as microfollicles in FNA, and some are more often classified as macrofollicles (Arch Pathol Lab Med 2006;130:148)
Cytology Images
Images hosted on other servers:

Microfollicular


Microfollicular

Macrofollicular

FNA and H&E

Round hyperchromatic nuclei

Positive Stains
Negative Stains
Electron Microscopy Images
Images hosted on PathOut server:

AFIP Images:

Abundant dilated endoplasmic reticulum

Microvilli project into well developed lumina

Signet ring follicular adenoma

Molecular / Cytogenetics Description
Videos


Histopathology Thyroid—Follicular adenoma (microfollicular)
by John R. Minarcik, M.D.
Differential Diagnosis