Thyroid Pathology

Question 1

What is histology?

Answer 1

• Samples of solid tissue – either biopsy or resection
• Fixed in formalin, then embedded in paraffin blocks
• Cut thinly and stained with Haemotoxylin and Eosin
• Tissue architecture and cytological features well preserved

Question 2

What is cytology?

Answer 2

• Material is sucked out of a lesion (aspirated) using a needle, fluid medium
• The material is then smeared straight onto a slide (direct preparation)
• Or centrifuged down and filtered before being applied to a slide (liquid based cytology)
• Can make a cell block (pellet of cells can be processed by histology) for ancillary testing

Question 3

What are the types of benign thyroid lesions?

Answer 3

• Multinodular Goitre (enlarged and nodular)
• Graves Disease
• Hashimotos Thyroiditis (hypothyroidism)
• Follicular adenoma (usually singular, no invasion)

Question 4

Describe multi-nodular goitre

Answer 4

-Most common thyroid disease
-Can cause hyperthyroidism as well as hypothyroidism
-Multilobulated asymmetrically enlarged glands
-Trying to produce more of thyroid products intermittently then involuting
=Dilated follicles (contain macrophages)
=Cholesterol clefts
=Variably sized follicles (tiny vs enlarged)
=Foamy macrophages
=Cystically dilated follicles
=Fibrous septae (in between follicles)

Question 5

Describe Graves’ Disease

Answer 5

-Also known as toxic nodular goitre
-Autoimmune disease with antibodies to thyroid stimulating hormone receptor
-Causes hyperthyroidism (stimulates gland)
=Papillary architecture (not follicles)
=Clinical and biochemical diagnosis (not made on histology)
=Cells (follicular epithelial cells) have more columnar appearance, basally located nucleus
=Bubble appearance, scalloping colloid

Question 6

Describe Hashimoto’s Thyroiditis

Answer 6

-Autoimmune process affecting the thyroid
-Associated with thyroglobulin and thyroid peroxidase antibodies
-Lymphoid predominant inflammation, follicular cell oncocytic change and variable degrees of gland destruction, disruption to parenchyma
=Lymphoid aggregates with germinal centre formation
=Small lymphocytes
=Oncocytic epithelial cells (looks pink)
=Fibrosis

Question 7

Describe Follicular Adenoma

Answer 7

-Completely encapsulated lesion
-Made up of thyroid follicles
-Clonal population but benign
-If capsular or vascular invasion then becomes follicular carcinoma
=No invasion of thick fibrous capsule
=Lesion made up of small, collapsed, colloid sparse follicles

Question 8

What are the types of malignant thyroid lesions?

Answer 8

-Follicular Carcinoma
-Papillary Carcinoma
Rare:
-Medullary Carcinoma
-Anaplastic Carcinoma

Question 9

What other thyroid tumours are there?

Answer 9

-Noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP)
=looks like follicular adenoma and nucleus like papillary carcinomas, dont behave like carcinomas so benign, low metastatic rate)
-Follicular adenoma & Hürthle cell adenoma= benign tumours with pink cytoplasm by numerous mitochondria
-Hyalinizing trabecular tumour= very rare, gene translocation

-Well differentiated tumour of uncertain malignant potential (WDT-UMP)
-Follicular tumour of uncertain malignant potential (FT-UMP)
-Follicular carcinoma & Hürthle cell carcinoma
-Papillary carcinoma
-Medullary carcinoma
-Poorly differentiated carcinoma
=specific entity, intermediate prognosis with anaplastic
-Anaplastic carcinoma
-Primary thyroid lymphoma
-Metastatic disease &
-Other rare tumours

Question 10

Describe follicular carcinoma

Answer 10

-Follicular adenoma but tumour invades through fibrous capsule, blood vessels (produced follicles)

Question 11

Describe papillary carcinoma

Answer 11

• Papillary structures (long fingers lined by malignant cells)
• Can be encapsulated
  1. Intranuclear inclusions
  2. Nuclear clearing and irregularity
  3. Nuclear grooves
• Psammoma bodies (calcified laminated bodies)
• Follicular variant (NIfTP)

Question 12

Describe medullary carcinoma

Answer 12

• Sometimes associated with genetic conditions (multiple endocrine neoplasia)
• Looks like anything, wide range of appearance (spindle like appearance, can have nuclear inclusion and grooves/ epethioid appearance)
• Amyloid associated! Congo red stain

Question 13

Describe anaplastic carcinoma

Answer 13

• Poor prognosis
• High grade malignancies
• Hyperchromatic

Question 14

Describe thyroid cytology

Answer 14

• Screening test only
• Most important features is colloid
• Cell to colloid ratio is a good indicator of malignancy (less= malignant)
• Colloid is a reassuring feature (benign, as malignant less)
• For adequacy must have 6 groups of at least 10 cells

Question 15

What is the Bethesda/Thy classification

(fine needle aspirate diagnoses)?

Answer 15

• Unsatisfactory, (not enough cells) (Thy1)
• Cyst fluid (not enough epithelium to identify histogenesis of cyst) (Thy1c)
• Non-neoplastic thyroid lesion (Thy2)
• Cyst in non-neoplastic lesion (Thy2c)
• Possible neoplasm thyroid (Thy3a)
• Probable or certain follicular neoplasm (Thy3f)- only in histology to differentiate
• Suspicion of malignant neoplasm (Thy4)
• Malignant neoplasm (Thy5)

Question 16

Describe the difference in appearance between benign and malignant in cytology

Answer 16

• Malignant= not much blue in background (less colloid) and microfollicular architecture, multinucleated cells, papillary structures, nuclear features
• Benign= blue colloid background, benign epithelial cells in sheet

Question 17

What are the key cytological features in FNA thyroid?

Answer 17

• Lots of colloid – multinodular goitre
• Variably sized follicles – multi-nodular goitre
• Even sized follicles – follicular neoplasm
• Papillary structures, nuclear grooves & inclusions – papillary carcinoma
• Dispersed small cells, stained for calcitonin – medullary carcinoma
• Very pleomorphic cells – anaplastic carcinoma

Question 18

What are the additional diagnostic aids?

Answer 18

-Cell block
-Immunohistochemistry
-Molecular pathology
=BRAF (papillary carcinoma), TERT (carcinoma marker), RAS (follicular lesions), gene fusions (trabecular lesions, papillary carcinoma)