Ch. 10 - Thyroid

Question 1

What percentage of adults have thyroid nodules? What proportion of nodules are malignant?

Answer 1

5% have palpable, >50% have nonpalpable nodules. Of these, <5% are malignant.

Question 2

What risk of neoplasm is conferred by “hot” nodularity? How can this be assessed?

Answer 2

Hot nodules are almost never malignant and should not be FNA’d. Evidenced by decreased serum TSH.

Question 3

What size criteria are used for thyroid nodule FNA eligibility? Any other features?

Answer 3

1cm; may biopsy smaller if suspicious-looking (microcalcifications).

Question 4

What are the complications of FNA of thyroid?

Answer 4

Hematoma (transient), infarction (rare), needle tract seeding (almost never)

Question 5

What are the criteria for specimen adequacy in thyroid FNA?

Answer 5

1. Presence of colloid
2. At least 6 clusters of at least 10 follicular cells
3. Any specific diagnosis

Question 6

What are the 6 categories of Bethesda thyroid reporting, their respective risk of malignancy, and their clinical consequence?

Answer 6

Unsatisfactory (1-5%, rebiopsy)
Benign (1-3%, follow)
AUS/FLUS (5-15%, rebiopsy)
Suspicious for FN (15-30%, resect)
Suspicious for malignancy (65%, resect)
Malignant (90%, resect).

Question 7

In general, what features favor malignancy on thyroid FNA?

Answer 7

Microfollicles, architectural atypia (noncohesiveness), papillae, pseudoinclusions & grooves. Psammoma bodies not so much.

Question 8

What thyroidal conditions may exhibit multinucleated giant cells?

Answer 8

Acute thyroiditis, granulomatous disease
Cystic degeneration
PTC
Anaplastic carcinoma

Question 9

What is the pathophysiology of multinodular goiter?

Answer 9

Thyroid-deficient state selects for hyperplastic follicular cells, resulting in multinodularity.

Question 10

What defines follicular adenoma?

Answer 10

Solitary nodule composed of follicular cells that are “morphologically distinct from surrounding gland” and does not exhibit invasion.

Question 11

What does the diagnosis of “benign follicular nodule” entail?

Answer 11

Could be MNG or follicular adenoma (indistinguishable). Used to indicate a benign lesion.

Question 12

Describe the cytology of a benign follicular nodule.

Answer 12

Macrofollicles with colloid and low cellularity. May have some Hurthle cells, cyst lining cells with macrophages. A little atypia is okay.

Question 13

Describe the cytology of Hashimoto’s thyroiditis.

Answer 13

Very cellular with mixed lymphoid infiltrate including dendritic cells and TBMs. Look for tangles (germinal centers). Hurthle cells are common. Colloid is scant.

Question 14

Describe the cytology of subacute (de Quervain) thyroiditis.

Answer 14

Multinucleated giant cells and rare granulomas (reniform/boomerang histiocytes) and lymphocytes.

Question 15

Describe the cytology of Riedel’s thyroiditis.

Answer 15

Usually a dry aspirate.

Question 16

What role does FNA play in thyroiditis?

Answer 16

Not recommended (or even needed) for diagnosis; only to rule out malignant lesions occurring in context of thyroiditis.

Question 17

What is “black thyroid”?

Answer 17

Dark brown pigmentation of thyroid due to tetracycline (eg. minocycline) use.

Question 18

Describe the cytologic features of radiation changes. How can it be distinguished from carcinoma?

Answer 18

Sheets of enlarged cells with high N:C, Hurthle cell change, cytoplasmic vacuolization, and marked nuclear atypia. However, microfollicles are uncommon.

Question 19

What role does FNA play for follicular neoplasms?

Answer 19

It is a SCREENING tool, not a diagnostic tool, and can only recommend excision for final diagnosis.

Question 20

What are the histologic features of follicular carcinoma?

Answer 20

Split into two subtypes; minimally and widely invasive. Capsular and vascular invasion are the defining features.

Question 21

What are the cytologic features of follicular carcinoma?

Answer 21

Marked cellularity, predominance of microfollicles and/or trabeculae, scant colloid.

Question 22

How do hurthle cell tumors cytologically differ from follicular neoplasms?

Answer 22

Look for more atypia, large nucleolus. Noncohesive with pseudopsammoma bodies.

Question 23

Recite the variants of papillary thyroid carcinoma.

Answer 23

Follicular, macrofollicular, oncocytic, Warthin-like, clear cell, diffuse sclerosing, columnar, tall-cell, solid, cribriform-morular, and fasciitis-like stroma.

Question 24

What are the underlying genetic features of PTC?

Answer 24

RET/PTC translocation, TRK rearrangements, RAS and BRAF point mutations. PAX/PPARy?

Question 25

Describe the cytology of PTC.

Answer 25

Sheets, papillae, or microfollicles of cells with grooves and pseudoinclusions. May have multinucleated giant cells and variable colloid.

Question 26

What are poorly differentiated carcinomas? What are their 3 histologic patterns? What are the defining features?

Answer 26

Malignant thyroidal carcinomas that fall in between the differentiated carcinomas and the anaplastic.

Insular, trabecular, and solid.

Ki67 is 10-30%, with 3+ mitoses per 10hpf

Question 27

Describe the cytology of anaplastic thyroid carcinoma

Answer 27

Obvious, whopping malignancy with extreme atypia, tumor diathesis…can’t mistake this.

Question 28

What is the significance of squamous cell carcinoma of the thyroid?

Answer 28

It affects the same patients as and behaves the same way as anaplastic thyroid carcinoma.

Question 29

What is the cell of origin of MTC? Who does it affect?

Answer 29

Parafollicular C cell

Most cases are actually sporadic (adult); only 10-20% are associated with MEN (peds cases)

Question 30

What are the HISTOLOGIC features of MTC?

Answer 30

Sheets, nests, or ribbons of variably shaped neuroendocrine nuclei (no nucleoli) frequently with pseudoinclusions and amyloid.

Question 31

What are the cytologic features of MTC?

Answer 31

Noncohesive cells with frequent pseudoinclusions and inconspicuous nucleoli. Look for amyloid and red cytoplasmic granules (calcitonin?)

Question 32

Why should MTC always be considered in lymph node evaluations?

Answer 32

50% of cases already have lymph nodal spread at the time of diagnosis.

Question 33

Who does thyroid lymphoma affect, and what are the patterns seen?

Answer 33

Patients with Hashimoto’s thyroiditis (confers 60x risk). Falls into EMZL, DLBCL, and mixed patterns.

Question 34

What are the cytologic features of EMZL of thyroid?

Answer 34

Look for numerous small lymphoid cells including centrocytes, plasma cells, and monocytoid B cells.

Question 35

What are the cytologic features of DLBCL of thyroid?

Answer 35

Look for large monotonous cells (centroblasts vs immunoblasts), maybe Burkitt’s-like cells.

Question 36

What are the most common metastases to thyroid?

Answer 36

Lungs, esophagus, breast, kidney

Question 37

What is the role of the AUS/FLUS category?

Answer 37

Describes entities that do not satisfy suspicious or malignant criteria. Try to keep to <7% of FNA diagnoses.

Question 38

Try to recall 8 scenarios appropriate for the diagnosis of AUS/FLUS.

Answer 38

Microfollicles with sparse overall cellularity
Hurthle cells with sparse overall cellularity
Hurthle cells with history of thyroiditis
Atypia hindered by artifact
Random nuclear atypia
Atypical cyst lining cells
Marked anisonucleosis
Atypical lymphoid infiltrate

Question 39

What are the cytologic features of parathyroid cells?

Answer 39

Cohesive sheets, ribbons, and acini of cells with coarsely granular chromatin and moderately granular cytoplasm. No colloid!

Question 40

What roles do molecular probe tests play in thyroid FNA?

Answer 40

Most valuable for elucidating suspicious and atypical cases that cannot be outright called malignant or benign.