JOURNAL CLUB PRESENTATION

Thanks to Dr. Babar YasinPG-IV For tis slide presentation

Pitfalls in the Diagnosis of Follicular Epithelial Proliferationsof the Thyroid

Ozgur Mete, MD*w and Sylvia L. Asa, MD, PhD*w

INTRODUCTIONDiagnosis of follicular epithelial neoplasms --- area

of controversy. Major issues:- Recognition of the diagnostic nuclear features of

papillary thyroid carcinoma and reactive cytologic atypia.

- Definitions of capsular invasion, vascular invasion, and extrathyroidal extension.

- Challenges related to oncocytic change, malignant transformation in benign nodules, focal dedifferentiation, and the application of ancillary tools in thyroid pathology.

ARE MORPHOLOGIC CRITERIA ABLE TODISTINGUISH HYPERPLASTIC FOLLICULARLESIONS FROM FOLLICULAR ADENOMAS?

Hyperplasia -- reversible processMorphologically hyperplastic follicular lesions:

-Multiple-Poorly encapsulated benign follicular epithelial proliferations

-Heterogeneous cytology and architecture - Indistinguishable from the surrounding parenchyma.

Follicular Neoplasms:- Solitary- Encapsulated follicular epithelial proliferations- Uniform cytology and architecture- Totally different from the surrounding parenchyma

- The distinction from follicular carcinoma is based on invasive behavior.

- Distinction from follicular variant papillary carcinoma is based on nuclear features

Follicular adenomas – monoclonal proliferations of follicular epithelia.

Hyperlasia – polyclonal proliferation of untransformed cells

Multiple monoclonal and polyclonal nodules coexist in multinodular goiters.

Some nodules may exhibit a distinct area of monoclonal proliferation in the background of polyclonal proliferation.

Malignancy occurs in the background of benign nodules in multinodular goiter as well as in solitary adenomas.

Benign nodules with prominent true papillary architecture, identified sometimes as solitary lesions but also in the setting of multinodular goiter, have been called “papillary hyperplastic nodules.”

Clonal lesions that harbor activating somatic mutations “hot” or “warm” on thyroid scan.

Benign nodules with papillary architecture are monoclonal and therefore they should be classified as a variant of follicular adenoma

Classical morphologic criteria to distinguish hyperplasia from adenoma are not valid in the setting of multinodular goiter.

The terminology been used to describe this disorder, includes “colloid nodules,” “adenomatoid nodules,” and the obviously incorrect “hyperplasic nodules.”

The author recommends the unifying terminology “follicular nodular disease” for the nodules of multinodular goiter

WHAT ARE THE CRITERIA FOR THE DIAGNOSISOF WELL-DIFFERENTIATED THYROIDCARCINOMA?

Papillary thyroid carcinoma – Nuclear featuresFollicular thyroid carcinoma - Capsular and/or vascular

invasion

Low magnification to analyze the “texture” of the thyroid nodules.

Texture - density of colloid, nuclear size, and contrast because of nuclear basophilia.

The second step is to decide if the lesion exhibits nuclear features of PTC.

In the absence of nuclear features of PTC, the diagnosis of malignancy (FTC) can be rendered when there is unequivocal evidence of capsular and/o vascular invasion.

WHAT ARE THE DIAGNOSTIC NUCLEARFEATURES OF PAPILLARY THYROIDCARCINOMA?

Nuclear EnlargementThe nuclear/cytoplasmic ratio is increased. Nuclear overlapping, nuclear crowding, and loss of

the basal polarization of nuclei.

The last feature is particularly important when dealing with benign follicular lesions that exhibit papillary architecture.

Nuclear Membrane IrregularitiesHallmark of PTC - loss of nuclear roundness. Oval or

elongated nuclei are one form of irregularity.

A “raisinoid” or “cerebriform” appearance, because of indentations, or “angulated” nuclear membrane irregularities, are important features of PTC.

The more nuclear membranes fold into themselves, the more florid nuclear features such as “grooves” or “intranuclear pseudoinclusions” .

The most florid feature, the intranuclear cytoplasmic pseudoinclusion, results from deep invaginations of the cytoplasm. (Not required)

NUCLEAR PSEUDO INCLUSION/ PSEUDO-PSEUDO INCLUSIONS

The diameter, content, and edge features of the inclusions.

The nuclear inclusion must contain material similar to the cell cytoplasm

It must have sharply defined edges

Peripheral Chromatin Margination Hypo chromatic nuclei because of peripheral margination of

chromatin and clearing of nucleoplasm

Chromatin margination results in the optically clear or ground-glass appearance of the nuclei.

Prominent Micronucleoli Multiple small eccentric micronucleoli that are distinct from

the single, usually central nucleolus of nontumorous thyroid follicular epithelial cells

WHAT OTHER FEATURES ARE CHARATERISTICOF PAPILLARY THYROID CARCINOMAS?

Architectural and Colloid Changes

Follicular variant PTCs often have distorted or irregularly shaped follicles.

This feature may be focal.They also usually contain thick, hypereosinophilic colloid that has a peculiar scalloped appearance at the periphery of the follicles

Multinucleated Giant Cells of MacrophageDerivation Not specific Benign conditions including palpation thyroiditis, de

Quervain’s thyroiditis, and at sites of previous fine-needle aspiration.

Psammoma BodiesHallmark of PTCBasophilic concentrically laminated spherical

bodies.The presence of psammoma bodies should prompt

a thorough search for other features of PTC

Identification of a psammoma body in a perithyroidal or cervical lymph node is a sign of micrometastatic PTC – Deeper levels.

HOW CAN REACTIVE CYTOLOGIC ATYPIA BE DISTINGUISHED FROM THE ATYPIA OF PAPILLARY THYROID CARCINOMA?

Areas of degeneration that contain hemorrhage, stromal fibrosis, foreign body material (such as talc after an FNA), lymphocytic infiltration, or hemosiderin-laden macrophages, may exhibit nuclear membrane nuclear irregularities that can mimic the nuclear features of PTC.

With the increasing use of FNA most lesions have areas of reactive change.

The acronym “WHAFFT” (worrisome histologic alterations following FNA of thyroid) has been used for these.

The diagnosis of PTC should be considered when nuclear atypia is seen well away from sites of degeneration.

The follicular epithelium of chronic lymphocytic thyroiditis exhibits nuclear alterations resembling those of PTC.

These changes occur within follicles that maintain a lobular architecture and are clearly reactive.

CAN BENIGN NODULES UNDERGO MALIGNANTTRANSFORMATION?

Benign nodules can sometimes exhibit unifocal or multifocal malignant transformation to follicular variant PTC.

Areas of reactive atypia in a degenerate nodule should be distinguished from areas of malignant transformation in a benign follicular nodule.

The identification of a single small focus of PTC in an otherwise benign lesion may represent a solitary focus of transformation or potentially a trapped pre-existing or unrelated papillary microcarcinoma and shoud be staged based on the size of the focus.

Follicular nodules – MULTIFOCAL ATYPIAThis may suggest multifocal transformation to

PTC.

Therefore staging based on the size of the entire nodule.

HOW SHOULD NODULES WITH ONCOCYTIC CHANGE BE CLASSIFIED?

Oncocytic change is not specific to any thyroid lesion.(Benign conditions such as thyroiditis, follicular nodular disease, or in thyroids of patients who have a previous history of head and neck radiotherapy or systemic chemotherapy.)

Oncocytic change is also seen in all forms of thyroid malignancies. Criteria for diagnosing oncocytic lesions are not different from those of their nononcocytic counterparts, including nuclear features of PTC or capsular and/or vascular invasion.

Oncocytes may have hyperchromatic nuclei and large, cherry-red nucleoli that can confound the diagnosis of PTC based on nuclear criteria.

Nuclear membrane irregularities is the main key to diagnose PTC in the absence of degeneration or inflammation.

Oncocytic and clear cell variants of medullary thyroid carcinoma (MTC) may easily mimic oncocytic and clear cell follicular lesions or neoplasms.

Nesting or insular architecture, Polygonal cells, Indistinct cell borders (well-defined cell borders of follicular epithelial cells).

Nuclei with salt-and-pepper chromatin.

Neuroendocrine secretory granules that give the cell cytoplasm a basophilic and/or amphophilic granular appearance (MTC) ----- Oncocytic change in follicular epithelial cells -- deeply eosinophilic granular cytoplasm and/or a degree of cytoplasmic clearing, which reflects the mitochondrial dilatation.

Fibrohyaline strands in between the tumor nests, and a discohesive or loosely cohesive pattern of tumor cells favors the diagnosis of MTC.

WHAT ARE THE DEFINITIONS OF CAPSULARAND VASCULAR INVASION?

Follicular epithelial neoplasm that exhibits capsular and/or vascular invasion in the absence of nuclear features of PTC is diagnosed as FTC.

Many pathologists consider a single focus of capsular invasion to be a sign of malignancy when nuclear features of PTC are absent.

Others have questioned if capsular without vascular invasion qualifies for a diagnosis of a malignancy??

Most experts require the presence of tumor penetrating through the entire thickness of the capsule of a lesion, others consider it sufficient to identify the presence of incomplete capsular Transgression.

Sites of previous biopsy can result in artefactual capsular dehiscence and pseudoinvasion.

Bulging of tumor under intact endothelium, intravascular tumor casts without thrombus and intravascular tumor nests covered with intact endothelium do not predict metastatic behavior.

Tumor cells invading through a vessel wall and thrombus adherent to intravascular tumor predicts an unusually high risk of distant hematogenous spread.

CAP

WHAT IS THE SIGNIFICANCE OFEXTRATHYROIDAL EXTENSION?

Although many people refer to invasion of a thyroid capsule by thyroid tumors, the only capsule that can be invaded is a tumor capsule. The thyroid gland has no anatomic capsule. Rather, the thyroid is covered by an incomplete thin pseudocapsule that contains varying proportions of fibrous and adipose tissue.

Criteria for defining minimal (pT3) extrathyroidal extension (ETE) are problematic, because the presence of tumor cells in fibroadipose tissue does not qualify as ETE.

The hallmark of ETE is at least skeletal muscle invasion in the lateral lobes.

Does not apply in the isthmus, because normal isthmic parenchyma includes skeletal muscle fibers of Soemmerring muscle intermingled with thyroid follicles.

The assessment of ETE in the isthmus requires input from preoperative and intraoperative findings in addition to histologic examination looking for invasion into other neck structures such as laryngeal cartilage or esophagus.

CAP The criteria defining minimally invasive follicular carcinoma

are controversial and still evolving. The WHO classification system allows for this term to encompass encapsulated lesions with capsular and/or small-caliber sized angioinvasion, even if angioinvasion is extensive.

However, it is apparent in the literature that even within this group there is a survival difference between tumors with only capsular invasion (so called “true minimally invasive” follicular carcinomas) and those that are angioinvasive, with the latter being more aggressive. It is thus appropriate to further stratify minimally invasive tumors into these subcategories.

HOW IS DEDIFFERENTIATION DEFINED ANDWHAT IS ITS SIGNIFICANCE?

Poorly differentiated thyroid carcinoma (PDTC) -- intermediate form of thyroid cancer between well-differentiated PTC or FTC and undifferentiated or anaplastic thyroid carcinoma.

The Turin consensus defined PDTC as a neoplasm derived from follicular epithelial cells with a solid/trabecular/insular growth pattern, absence of conventional nuclear features of PTC and presence of at least one of the following features:

- convoluted nuclei- mitotic activity (>3/10HPF)- necrosis.

This consensus did not clarify precisely the required minimum percentage of these changes to classify a follicular neoplasm as PDTC.

Because the clinical course will be driven by the presence of the worst component, Authors believe that any amount of dedifferentiation should be reported in the surgical pathology consultation report.

“PTC/FTC with focal dedifferentiation” when these changes occur in <30% of an otherwise well-differentiated thyroid carcinoma.

Lesions with more than this component are diagnosed as poorly differentiated carcinoma, and authors specify it as “arising in PTC or FTC” if there is an associated well-differentiated component

WHEN SHOULD ANCILLARY TOOLS BE USED INTHE DIAGNOSIS OF DIFFERENTIATEDFOLLICULAR EPITHELIAL NEOPLASMS?

Immunohistochemisty is usually used to identify the cellular origin of a thyroid lesion, to support the diagnosis of malignancy, to predict the risk of lymph node metastasis, or to highlight nuclear membrane changes.

Thyroglobulin is the most specific marker for thyroid follicular epithelium (technical limitations because of its tendency to diffuse widely throughout adjacent tissue)

TTF-1 is positive in both follicular epithelial cells and parafollicular C-cells. TTF-1 is also characteristically found in lung carcinomas and some high-grade neuroendocrine carcinomas from other sites.

Markers of neuroendocrine differentiation (including synaptophysin and chromogranins) are positive in MTC, intrathyroidal parathyroid lesions, paragangliomas, or metastatic neuroendocrine carcinomas.

The presence of tyrosine hydroxylase and the negativity for low molecular weight keratins supports the diagnosis of paraganglioma.

Positivity for monoclonal carcinoembryonic antigen and calcitonin is diagnostic of MTC.

Parathyroid lesions are distinguished by their immunoreactivity for PTH and Gcm2 (glial cells missing 2).

If the lesion is clearly of thyroid follicular cell derivation, but malignancy is not unequivocal, there are several useful markers that can be applied. HBME-1, cytokeratin 19 (CK19), and galectin-3 are useful to support the diagnosis of malignancy

HBME-1 positivity with an apical and/or membranous pattern is suggestive of malignancy, but when negative, it does not exclude malignancy.

Diffuse and membranous CK19 throughout the lesion is usually helpful, but focal strong staining can be seen at sites of degeneration and diffuse strong staining is common in lymphocytic thyroiditis, so careful assessment of the pattern of reactivity is important.

Recently, emerin immunohistochemistry has been used to highlight nuclear membrane irregularities seen in PTC.

Molecular testing for BRAF mutations and RET/PTC gene rearrangements can be applied to cytology and histology specimens from suspicious thyroid nodules.

Image analysis using genetic programming software (GPS) is a new and evolving ancillary tool that builds automatic feature extraction algorithms, utilizing spectral and spatial signatures of image features.

The authors have undertaken a feasibility study to analyze the texture pattern of follicular variant PTC and benign follicular lesions using GPS. The preliminary results are promising, as GPS can recognize benign and malignant areas in digitalized hematoxylin and eosin–stained slides.

Ongoing studies will be needed to validate this exciting new technology