Thyroid cytopathology

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Thyroid cytopathology is a large part of cytopathology.

This article deals only with thyroid cytopathology. An introduction to cytopathology is in the cytopathology article. Head and neck cytopathology is dealt with in the Head and neck cytopathology article.

Normal

Follicular cells:

  • Uniform spacing of cells.
  • "Cracks" (spaces) between cell - "crazy paving".[1]

Colloid - acellular crap with:

  • Irregular/sharp borders.
  • Cracks - key feature.
  • Dark (uniform) staining with Romanowsky type stains.
    • Green edge + red/orange centre with Pap stain.
  • +/-Entraped red blood cells (RBCs).

Note:

  • It is interesting that uniform spacing in the context of thyroid is benign... in breast suggests DCIS.

Standard sign-out language

There is a standard way of describing entities on thyroid cytology (from a National Cancer Institute (NCI) consensus conference):[2]

Preferred (NIC) Alternate (NIC) Plain language Risk of malignancy Usual management
Benign - Benign ~ 1% Follow/nothing
Follicular lesion of undetermined significance 1. Atypia of undetermined significance
2. Rule-out neoplasm
3. Atypical follicular lesion
4. Cellular follicular lesion 		Uncertain, favour benign 5-10% Repeat FNA in 3 months
Follicular neoplasm Suspicious for follicular neoplasm Uncertain, favour malignant 20-30% Hemithyroidectomy
Hurthle cell neoplasm Suspicious for Hurthle cell neoplasm Uncertain, favour malignant 20-30% Hemithyroidectomy
Suspicious for malignancy - Probably malignant 50-75% Repeat vs. hemithyroidectomy
Malignant - Cancer ~ 99% Excise
Nondiagnostic - Lesion missed or inadequate Unknown Repeat FNA in 3 months

Lymphocytic thyroiditis

Microscopic

Features:

  1. Lymphocytes not typical of circulating blood:
    • Centrocytes.
      • Small lymphocytes with a cleft.
    • Centroblasts.
      • Large lymphocytes with nucleolus and eccentric nucleus.
    • Plasma cells.
      • Cells with a "clockface nucleus".
  2. Small mature lymphocytes in fragments of follicular cells - raise the suspicion of lymphocytic thyroiditis.[3]
    • Small mature lymphocytes are not a reliable indicator of inflammation, as cells may layer during tissue preparation.[4]

Notes:

  • Usually #1 and #2 are seen.

Hashimoto's thyroiditis

Associations:[1][5]

  • AMA +ve.
  • Antithyroid antibody +ve.
    • Antimicrosomal (antithyroid peroxidase).
    • Antithyroglobulin.
  • Increased risk of B-cell lymphoma.

Features:[1]

  • Polymorphous lymphoplasmacytic infiltrate with germinal centres.
  • Tingible body macrophages.
    • Found in germinal centres; have condensed chromatin fragments.[6]
  • Lymphoid tangles.
    • Found in almost 100% of cases.[5]
  • Lymphoglandular bodies.
    • Cytoplasmic fragment of a lymphoid cell.[7]

Diagnosis

  • This is a clinical diagnosis.
    • It should be reported by the pathologist as "lymphocytic thyroiditis".

Papillary carcinoma

  • Papillary thyroid carcinoma is basically the only entity (in cytopathology) that has near universally accepted criteria.
    • This is why radiation oncologists say... "Basing stuff on pathology is like basing something on shifting sand."

Cytology

Criteria for papillary thyroid carcinoma:[8][9]

  1. Nuclear inclusion (really pseudoinclusions):[10]
    1. Edge of inclusion must be sharp (nuclear membrane-like).
    2. Size: at least 1/4 of the nucleus.
    3. Round, regular.
    4. Within epithelial cell.
    • Additional criteria:[11] Inclusion center should match cytoplasm.
  2. Nucleoli (micro or macro).
  3. Nuclear grooves.
    • No universal criteria; some believe grooves should go from edge-to-edge, i.e. across the nucleus.
  4. Nuclear enlargement.
  5. Changes in chromatin - patterns:
    • Granular.
    • Washed-out.

Additional features:

  • Papillary architecture (not commonly seen).
    • Clump of epithelial cells with attached fibrous tissue "tail" - that has a smooth edge.
  • Cellular/nuclear membrane overlapping; cells do not respect one another (very common).
  • +/-Psammoma bodies (uncommon - but helpful if seen).

Notes:

  • Nuclear enlargement may be seen in Hashimoto's disease.[12]
  • Nuclear grooves may be seen in Hashimoto's disease.[13]
  • Papillary architecture may be seen in Graves's disease.[14]

Variants of PTC

  • Tall cell variant.
    • May mimic Hurthle cell neoplasm.
  • Warthin-like variant.
    • Superficially resembles Warthin tumour (presence of lymphocytes).
  • Follicular variant of PTC; memory device ECT: Elongation, Clearing, Thick membranes.
    • Nuclear elongation.
    • Chromatin clearing.
    • Thick nuclear membranes.
      • Classic features of PTC (esp. pseudo-inclusions) are usually scarce in this variant.

Follicular neoplasm

  • Sort of a garbage category for the thyroid.

Cytology

Features:[2]

  1. Hypercellular lesion.
  2. 3-dimensional clusters of cells.
  3. Nuclear overlap/crowding.
  4. +/-Microfollicles, numerous.
    • Microfollicles are defined as: <15 cells forming at least two thirds of a circle.
  5. +/-Atypia marked.

Diagnosis (follicular neoplasm) per MB:

  • Either: 1-3 or 3-5.

Notes:

  • A few microfollicles are normal.
  • Atypia alone - "suspicious for malignancy" or "malignant".

Management:

  • Hemithyroidectomy.

Oncocytic neoplasm (Hurthle cell neoplasm)

General:

  • Oncocytic perferred by WHO over Hurthle cell.

Features:[2]

  1. Single cells or sheets of oncocytic cells.
    • 3-D clusters.
    • +/-Transgressing vessels - cluster of oncocytes surrounding vessels.
  2. Oncocytic cells:
    • Well-defined cellular borders.
    • Finely granular abundant cytoplasm.
    • Nucleoli, may be prominent.

Notes:

  • Benign (oncocytic) thyroid tissue may have:
    • Significant nuclear pleomorphism.
    • Multinucleation.

Diagnosis by MB:

  • If single cells -- need abundant.

Image:

Medullary thryoid carcinoma

  • May be familial - associated with MEN II syndrome.

Cytology

Features:[2]

  1. Single or loosely cohesive cells.
    • Spindle cell morphology common.
  2. Abundant eosinophilc granular cytoplasm - key feature
  3. Salt and pepper chromatin - key feature; no nucleoli.
  4. Nucleus eccentric and round/oval - plasmacytoid appearance.
  5. Amyloid - acellular, amorphous material may be present; cotton candy-like.
    • May be confused with fibrin...
      • Fibrin = fluffy edge vs. amyloid = sharp border. (???)
      • Fibrin - associated with PMNs/has PMNs within it.
    • Amyloid cannot be definitively differentiated on morphologic grounds from colloid.
    • Described by Halliday et al. as:[15]
      • Romanowsky type staining: "amorphous, irregular, waxy basophilic to metachromatic clump".
      • Pap staining: "cyanophilic-organophilic clumps of material + occasional prominent fissures".

Notes:

  • May have pseudoinclusions - mimic papillary thyroid carcinoma.[16]

DDx:

  • Anaplastic carcinoma.

Images:

IHC

  • Calcitonin +ve - it arises from C cells (which produce calcitonin)
  • CEA +ve (often better staining than calcitonin).[17]
  • Congo-red +ve (if amyloid present) - mnemonic: CRAP -- congo red amyloid protein.

Anaplastic carcinoma

  • Prognosis: very crappy.

Cytology

Features:

  • Nuclear atypia - marked.
  • Spindle cell morphology common.
  • Nucleolus.
  • Usually scant cellularity.[18]
  • Necrosis very common.

DDx:

  • Medullary carcinoma.

See also

References

  1. ↑ 1.0 1.1 1.2 Lefkowitch, Jay H. (2006). Anatomic Pathology Board Review (1st ed.). Saunders. pp. 672. ISBN 978-1416025887.
  2. ↑ 2.0 2.1 2.2 2.3 Baloch ZW, LiVolsi VA, Asa SL, et al. (June 2008). "Diagnostic terminology and morphologic criteria for cytologic diagnosis of thyroid lesions: a synopsis of the National Cancer Institute Thyroid Fine-Needle Aspiration State of the Science Conference". Diagn. Cytopathol. 36 (6): 425-37. doi:10.1002/dc.20830. PMID 18478609.
  3. ↑ GD. 2 February 2010.
  4. ↑ SB. ~29 January 2010.
  5. ↑ 5.0 5.1 Poropatich C, Marcus D, Oertel YC (1994). "Hashimoto's thyroiditis: fine-needle aspirations of 50 asymptomatic cases". Diagn. Cytopathol. 11 (2): 141-5. PMID 7813361. http://www3.interscience.wiley.com/journal/112701408/abstract?CRETRY=1&SRETRY=0.
  6. ↑ MacLennan I.C.M (1994). "Germinal Centers". Annual Review Immunology 12: 117-139. PMID 8011279.
  7. ↑ http://www.definition-of.com/lymphoglandular+body
  8. ↑ SM. 12 January 2010.
  9. ↑ Kini SR. Guides to clinical aspiration biopsy: thryoid. 2nd Ed. 1996. P.134.
  10. ↑ Boerner SL, Asa SL. Biopsy Interpretation of the Thyroid. Lippincott williams & Wilkins. ISBN 978-0-7817-7204-4. PP.112-3.
  11. ↑ SB. 8 January 2010.
  12. ↑ WG. 8 January 2010.
  13. ↑ WG. 8 January 2010.
  14. ↑ Biopsy Interpretation of the Thyroid. PP.97-98.
  15. ↑ Halliday BE, Silverman JF, Finley JL (April 1998). "Fine-needle aspiration cytology of amyloid associated with nonneoplastic and malignant lesions". Diagn. Cytopathol. 18 (4): 270–5. PMID 9557261. http://www3.interscience.wiley.com/cgi-bin/fulltext/39158/PDFSTART.
  16. ↑ URL: http://www.papsociety.org/guidelines/Morphologic%20criteria.doc. Accessed on: 28 April 2010.
  17. ↑ SB. 7 January 2010.
  18. ↑ GS. March 2, 2010.
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