- Divided into lobules of 20 - 40 round to oval follicles, each 50 - 500 microns, with a single layer of cuboidal to low columnar epithelium
- Lumen contains colloid, which is scalloped and pale in follicles with active secretory activity, densely eosinophilic in inactive follicles and more flocculent ("like a clump or tuft of wool") and basophilic in elderly
- Stroma contains C cells, formerly called parafollicular cells (actually are intrafollicular), derived from neural crest
- C cells represent 0.1% of gland, produce calcitonin, are present in middle and upper third of lateral lobes along central axes, are not present in extreme upper and lower poles or in isthmus
- Usually 10 C cells per low power field in adults
- C cells are more numerous in neonates, decrease in adults, increase and appear as nodular aggregates after age 60 years
- C cells have pale / clear cytoplasm, oval nuclei, difficult to identify with H&E, use calcitonin stain
- Sanderson's polsters: collections of small follicles projecting into lumen of large actively secreting follicles; may resemble papillary carcinoma
- Oncocytes (Hürthle cells, oxyphilic cells, Ashkenazy cells): large cells with abundant deeply eosinophilic granular cytoplasm and numerous mitochondria
Oncocytes
Sanderson's polster
Thyroid follicular epithelium
Follicular colloid
Normofollicular thyroid
Macrofollicular thyroid
Microfollicular thyroid
Pyramidal lobe
Pericapsular fat
Adipose metaplasia
Perithyroid thyroid follicles
Intrathyroidal muscle
Calcium oxalate crystals in the colloid
PAS staining
Mucicarmine staining
Thyroglobulin expression
TTF1 expression
PAX8 expression
TTF2 nuclear expression
NIS membranous expression
Cluster of C cells
Location of C cells in relation to follicle
Pericapillary location of C cells
Clustered distribution of C cells
Calcitonin immunohistochemistry
Proliferation in adult thyroid
Prominent vascular network
Capillary network
Solid cell nests
Histologic mimics of SCN
Solid cell nests: p63
Solid cell nests: thyroglobulin-
Images from AFIP:
stain); cells are
polyhedral and
spindled
Follicles lined by flattened epithelium
Normal adult follicles are round to oval
Follicles lined by cuboidal epithelium
Colloid is flocculent - most likely artifactual, not significant
Tangential section
of normal thyroid
follicle may resemble
C cell hyperplasia
Images hosted on other servers:
Follicles lined by flattened epithelium and filled with colloid
Rich vascular supply
Thyroid and parathyroid glands
Papillary structures
C cells (calcitonin stain)
- Follicular cells: thyroglobulin (very specific, weaker staining in oncocytic cells), TTF1, low molecular weight keratin; also EMA, vimentin, T3 (triiodothyronine), T4 (thyroxine), ER beta (not alpha), PgR
- Note: thyroglobulin may leak out of follicular cells and create false positivity in adjacent cells
- Colloid: thyroglobulin, Alcian blue, PAS, T3, T4
- C cells: calcitonin, calcitonin gene related peptide (CGRP), neuron specific enolase, chromogranin A, synaptophysin, CEA, somatostatin; C cells are metachromatic with toluidine blue; C cells are NEGATIVE for thyroglobulin
- Follicular cells: abundant granular endoplasmic reticulum, well developed Golgi, prominent lysosomes, luminal (apical) microvilli, well developed desmosomes with terminal bars between cells, small mitochondria, may contain lipofuscin; nuclei are round with homogeneous chromatin
- C cells: intrafollicular (separated from thyroid interstitium by follicular basal lamina), numerous dense core neurosecretory granules (type I are 280 nm, moderately electron dense and present in most C cells; type II are 130 nm, more electron dense and rare)
Images from AFIP:
Follicles have luminal microvilli
Intrafollicular C cell
Images hosted on other servers:
Follicular cells
"Shotgun Histology Thyroid"
by John R. Minarcik, M.D.
