Thyroid gland

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The thyroid gland is an important little endocrine organ in the anterior neck. It is not infrequently afflicted by cancer... but the common cancer has such a good prognosis there is debate about how aggresively it should be treated. The cytopathology of the thyroid gland is dealt with in the thyroid cytology article. It frustrates a significant number of pathologists, as the criteria for cancer are considered a bit wishy-washy.

Thyroid specimens

They come in 3 common varieties:

  • Hemithyroid.
    • Done to get a definitive diagnosis.
    • May be a "completion" - removal of the other half following definitive diagnosis.
  • Total thyroid.
    • Done for malignancy or follicular lesion.
  • FNA (fine needle aspiration).
    • done to r/o malignancy.

Gross pathology:

  • White nodules - think:
    • Lymphoid tissue.
    • Papillary thyroid carcinoma - may be calcified.[1]

Common diagnoses

  • Nodular hyperplasia.
  • Lymphocytic thyroiditis.
  • Papillary thyroid carcinoma -- most common cancer.
  • Follicular adenoma.
  • Follicular thryoid carcinoma.
  • Parathyroid tissue.

Parathyroid tissue

General:

  • Identification of normal can be tricky.

Features:[2]

  • Low power:
    • May vaguely resemble lymphoid tissue - may have hyperchromatic cytoplasm.
      • Does not have follicular centres like a lymph node.
    • May form gland-like structure and vaguely resemble the thyroid at low power.
    • Cytoplasm may be clear[3] - key feature.
    • Surrounded by a thin fibrous capsule.
  • High power:
    • Mixed cell population:[4]
      • Chief cells - predominant cell type, small, cytoplasm has variable staining (hyperchromatic-clear-eosinophilic).
      • Oxyphil cells (acid staining cells[5]) - abundant cytoplasm.
      • Adipocytes - increased with age, may be used to help differentiate from thyroid - key feature.


Name Staining (cytoplasm) Quantity of cells Cytoplasm (quantity) Function
(parathyroid) chief cells intense hyperchromatic to eosinophilic (see note) abundant moderate manufacture PTH
oxyphil cells moderate/light hyperchromatic to eosinophilic rare abundant ?

Notes:

  • Cytoplasmic staining varies considerably on H&E preparations - it may vary from hyperchromatic[6] to clear to eosinophilic[7].
  • Chief cells tend to stain more intensely than oxyphil cells.

Thyroid vs. parathyroid (see: parathyroid image):

  • Parathyroid cytoplasm:
    • Hyperchromatic.

Parathyroid vs. lymphoid tissue (see parathyroid image):

  • Parathyroid:
    • No germinal centres.
    • Gland-like/follicular-like arrangement -- much smaller than normal follicles of
    • Occasional cell with rim of clear cytoplasm (oxyphil?).

Images:

Benign

Nodular hyperplasia

  • Very common benign diagnosis.
    • If you've seen a handful of thyroids you've seen this.
  • Follicles of variable size.
  • Nodules maybe well circumscribed (on gross), but do not have a thick fibrous capsule.
  • Negatives:
    • No nuclear features suggestive of malignancy (papillary carcinoma).
    • Not cellular.

Follicular adenoma

  • Most common neoplasm of thyroid[8]
  • Encapusled lesion (surrounded by fibrous capsule).
  • Cellular.
  • Negatives
    • No nuclear features suggestive of papillary carcinoma.

Graves disease

  • Often misspelled "Grave's disease".
  • Hyperthyroidism.
  • Etiology: autoimmune.
  • Gross:[9].
    • Enlarged 50-150 g.
    • "Beefy-red" appearance, looks like raw beef.

Granulomatous thyoiditis

Features:[10]

  • AKA de Quervain disease.
  • Women > men.

Ridel thyroiditis

Hashimoto's thyroiditis

Clinical

Presentation:

  • Hypothyroid

Associations:[11]

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

Etiology

  • Autoimmune.
    • Often genetic/part of a syndrome.

Diagnosis

  • Histologically often not possible to separate from "nonspecific" thyroiditis.[12]
  • Nuclear clearing common - ergo may confuse with papillary carcinoma.
  • Polymorphous lymphoplasmacytic infiltrate with germinal centres.[13]

Malignant neoplasm

There are a bunch of 'em. The most common, by far, is papillary.

Papillary

Clinical

Basic clinican knowledge - P's:

  • Palpable nodes.
  • Popular (most common malignant neoplasm of the thyroid).
  • Prognosis is good.
  • Pre-Tx iodine scan.
  • Post-Sx iodine scan.
  • Psammoma bodies.

Notes:

  • Associated with radiation exposure.[14]

Histology

  • The key diagnostic features are nuclear changes.
    • "Shrivelled nuclei"/"raisin" like nuclei, nuclei with a wavy nuclear membrane.
    • Nuclear grooves.
    • Nuclear inclusions.
    • Nuclear clearing (only on permanent section) - also known as "Orphan Annie eyes".
  • Overlap of nuclei - "cells do not respect each other's borders" (easy to see at key feature at low power).
  • Classically has papillae (nipple-like shape).
    • Absence of papillae does not exclude diagnosis.
  • Psammoma bodies.
    • Circular, acellular, eosinophilic whorled bodies.
    • Not necessary to make diagnosis.
    • Arise from infarction & calcification of papilla tips.[15]

Notes:

  • Psammoma bodies are awesome if you see 'em, i.e. useful for arriving at the diagnosis.
    • If there are no papillae structures -- you're unlikely to see psammomas.
  • At low power look for cellular areas/loss of follicles.
  • Nuclear clearing seen in:
    • Hashimoto's and papillary thyroid carcinoma.[16]
    • May be an artifact of fixation/processing.
  • Nuclear overlapping is easy to see at lower power-- should be the tip-off to look at high power for nuclear features.
  • Nuclear inclusions are quite rare and not required to make the diagnosis -- but a very convincing feature if seen.

Subtypes if papillary

There are many.

Tall cell variant

Features:[17]

  • 50% of cells with height 2x the width.[18][19]
    • There is some disagreement on these criteria.[19]
  • Eosinophilic cytoplasm.
  • Well-defined cell borders.
  • Nucleus stratified; basal location, i.e. closer to the basement membrane.

Negative:

  • Nuclei not pseudostratified, if pseudostratified consider columnar cell variant.

Columnar cell variant

Epidemiology:

  • Poor prognosis.

Features:

  • Elongated nuclei (similar to colorectal adenocarcinoma) - key feature.
  • Pseudostratification of the nuclei (like in colorectal adenocarcinoma), differentiates from tall cell variant - key feature.
  • "Minimal" papillary features.
  • "Tall cells".
  • Clear-eosinophilic cytoplasm.
  • Mitoses common.

Image: Tall cell variant Pa ca (wiley.com).

Follicular variant

May be confused with follicular carcinoma or follicular adenoma.

Features:

  • Prominent follicles.

Cribriform-morular variant

Features:

  • Cribriform pattern.
  • Morules - balls of tissue.

Insular carcinoma

General:[20]

  • Rare - approximately 5% of all thyroid carcinomas.
  • Thought to be a separate tumour from papillary thyroid carcinoma and follicular thyroid carcinoma with a focal insular pattern.
  • Some lump this entity with papillary carcinoma, i.e. consider it a variant of papillary thyroid carcinoma.

Features:[20]

  • Islands of cells - key feature.
  • Scant cytoplasm.
  • Nuclei monomorphic and round.

DDx:[21]

  • Medullary thyroid carcinoma.
  • Poorly differentiated thyroid carcinoma.

Follicular thyroid carcinoma

Clinical

  • FNA NOT diagnosable.
  • Far away mets (sometimes).
  • Female predominant.
  • Favourable prognosis.

Histology

  • IMPOSSIBLE to differentiate from follicular adenoma on FNA (no cytologic differences).
  • Defined by invasion through the capsule.

Medullary thyroid carcinoma

  • Abbreviated MTC.

Clinical

3 M's:

Epidemiology

  • Very rare.
  • Poor prognosis.
  • May be genetic (MEN IIa/b syndrome).
  • Arises from C cells (which produce calcitonin).

Histology

Features:

  • Nuclei with "neuroendocrine features".
    • Small, round nuclei.
    • Coarse chromatin (salt and pepper nuclei).
  • Amyloid deposits - fluffy appearing acellular eosinophilic material in the cytoplasm.
  • C-cell hyperplasia (associated with familial forms of MTC).
    • C cells (AKA parafollicular cell): abundant cytoplasm - clear/pale.

IHC:[22]

  • Calcitonin +ve - it arises from C cells (which produce calcitonin)
  • Congo-red +ve (amyloid present) - mnemonic: CRAP -- congo red amyloid protein.
  • Neuroendocrine markers.
  • CEA +ve (often better staining than calcitonin).[23]

Image:

Anaplastic thyroid carcinoma

Epidemiology

  • Very rare.
  • Horrible prognosis.

Histology

Features:

  • Cytologically malignant:
    • Huge NC ratio.
    • Mitoses.
    • +/-Necrosis.

IHC

  • Keratin (AE1/AE3).
  • Vimentin +ve, >90%.[24]
  • Thyroglobulin - rarely +ve (~15%).[24]
  • CEA -ve, calcitonin -ve; to r/o medullary.

Thyroid IHC - general comments

  • Not really useful.
  • Papers with very small sample sizes abound.

Follicular thyroid carcinoma vs. papillary thyroid carcinoma

  • CD31 more frequently positive in follicular lesions.[25]
    • CD31 is a marker for microvessel density.
  • Galectin-3 thought to be positive in papillary carcinoma.[25]
  • HBME-1 thought to be positive in papillary lesions.[26]

See also

References

  1. ↑ BEC. 20 October 2009.
  2. ↑ http://www.medicalhistology.us/twiki/pub/Main/ChapterFourteenSlides/b56b_parathyroid_40x_he_labeled.jpg
  3. ↑ http://pathology.mc.duke.edu/research/Histo_course/parathyroid2.jpg
  4. ↑ http://www.bu.edu/histology/p/15002loa.htm
  5. ↑ http://dictionary.reference.com/search?q=oxyphil%20cell
  6. ↑ http://www.deltagen.com/target/histologyatlas/atlas_files/endocrine/parathyroid_and_thyroid_glands_20x.jpg
  7. ↑ http://instruction.cvhs.okstate.edu/Histology/HistologyReference/hrendo.htm
  8. ↑ EP P.51
  9. ↑ EP P.30
  10. ↑ Sternberg P.559
  11. ↑ 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.
  12. ↑ Sternberg P.560.
  13. ↑ APBR P.672.
  14. ↑ Sternberg P.564
  15. ↑ Sternberg P.565
  16. ↑ Sternberg P.566
  17. ↑ Urano M, Kiriyama Y, Takakuwa Y, Kuroda M (April 2009). "Tall cell variant of papillary thyroid carcinoma: Its characteristic features demonstrated by fine-needle aspiration cytology and immunohistochemical study". Diagn. Cytopathol.. doi:10.1002/dc.21086. PMID 19373912.
  18. ↑ http://pathologyoutlines.com/thyroid.html#tallcellvariant
  19. ↑ 19.0 19.1 Ghossein R, Livolsi VA (November 2008). "Papillary thyroid carcinoma tall cell variant". Thyroid 18 (11): 1179–81. doi:10.1089/thy.2008.0164. PMID 18925842.
  20. ↑ 20.0 20.1 Rufini V, Salvatori M, Fadda G, et al. (September 2007). "Thyroid carcinomas with a variable insular component: prognostic significance of histopathologic patterns". Cancer 110 (6): 1209–17. doi:10.1002/cncr.22913. PMID 17665497.
  21. ↑ Endo. fellow. 17 September 2009.
  22. ↑ http://pathologyoutlines.com/thyroid.html#medullary
  23. ↑ SB. 7 January 2010.
  24. ↑ 24.0 24.1 Ordóñez NG, El-Naggar AK, Hickey RC, Samaan NA (July 1991). "Anaplastic thyroid carcinoma. Immunocytochemical study of 32 cases". Am. J. Clin. Pathol. 96 (1): 15–24. PMID 1712540.
  25. ↑ 25.0 25.1 Rydlova, M.; Ludvikova, M.; Stankova, I. (Jun 2008). "Potential diagnostic markers in nodular lesions of the thyroid gland: an immunohistochemical study.". Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub 152 (1): 53-9. PMID 18795075.
  26. ↑ Papotti, M.; Rodriguez, J.; De Pompa, R.; Bartolazzi, A.; Rosai, J. (Apr 2005). "Galectin-3 and HBME-1 expression in well-differentiated thyroid tumors with follicular architecture of uncertain malignant potential.". Mod Pathol 18 (4): 541-6. doi:10.1038/modpathol.3800321. PMID 15529186.
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