Thyroid & parathyroid
Benign thyroid neoplasms
Follicular adenoma
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PubMed search: follicular adenoma thyroid
- 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)
- Adults, usually 20 - 50 years
- M:F = 1:6
- 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)
- Patient is usually euthyroid
- Usually "cold" nodule, may be "warm" but rarely "hot"
- 29 year old woman with clear cell follicular adenoma of ectopic thyroid (Endocr Pathol 1998;9:339)
- 45 year old woman with follicular adenoma with papillary architecture (Cytopathology 2015;26:256)
- 48 year old woman with renal cell carcinoma metastatic to follicular adenoma of thyroid gland (Acta Cytol 2004;48:64)
- 59 year old woman with metastasis to thyroid follicular adenoma (Pathol Int 2005;55:574)
- 61 year old man with clear cell follicular adenoma of thyroid (Exp Clin Endocrinol Diabetes 2010;118:19)
- Lobectomy (not enucleation)
- 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
Contributed by Andrey Bychkov, M.D., Ph.D., Mark R. Wick, M.D.
Encapsulated nodule
Grossing and sampling
AFIP images
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
Well encapsulated
Central scar
Cystic and partially necrotic tumor
- 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
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Contributed by Andrey Bychkov, M.D., Ph.D., Mark R. Wick, M.D., Asmaa Gaber Abdou, M.D.
Abundant crystals of calcium oxalate
Calcium oxalate crystals
Processing artifact with distorted nuclei
Distorted nuclei due to technical / processing artifact
Tissue degeneration
Various images
Cellular follicular adenoma
Trabecular type
AFIP images
Thin and uniform fibrous capsule
Marked fibrosis and stromal hyalinization
Marked hyaline thickening of vessel walls
Marked fibrosis, hyalinization and calcium deposition
Marked vascularization
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:
B: trabecular,
C: microfollicular,
D: macrofollicular
Left: macrofollicular, right: solid pattern
Signet ring
Atypical adenomas:
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
Stains:
follicular adenoma
is thyroglobulin+
(AFIP)
Signet ring pattern, Alcian blue+
Images hosted on other servers:
Adjacent atrophic follicular epithelium
Clear cell adenoma
Patterns:
Macrofollicular
Microfollicular
Microfollicular
Encapsulated microfollicular adenoma
Insular
Spindle cell type
- 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)
Contributed by Ayana Suzuki, C.T.
Microfollicles
Images hosted on other servers:
Microfollicular
Microfollicular
FNA and H&E
Round hyperchromatic nuclei
- Thyroglobulin
- Low molecular weight cytokeratin
AFIP images
Abundant dilated endoplasmic reticulum
Microvilli project into well developed lumina
Signet ring follicular adenoma
- Clonal
- Occasionally tetraploid or aneuploid (Am J Clin Pathol 1990;94:527)
Solitary thyroid nodule
Thyroid: compare and contrast
Histopathology thyroid: follicular adenoma (microfollicular)
- Follicular variant of papillary carcinoma: has nuclear features of papillary carcinoma
- Minimally invasive follicular carcinoma
- Nodular hyperplasia with dominant nodule: hyperplastic changes elsewhere in gland, often not encapsulated
