Endocrine Pathology Practice Questions

Q: What is the most common carcinoma of the thyroid?

Papillary thyroid carcinoma. ***Papillary thyroid carcinoma*** - This is the **most common type** of thyroid cancer, accounting for approximately 80-85% of all thyroid malignancies [1], [2]. - It typically has an **excellent prognosis** due to its relatively slow growth and tendency to metastasize through lymphatics rather than hematogenously [2]. *Follicular thyroid carcinoma* - This is the **second most common** type of thyroid cancer, comprising about 10-15% of cases [2]. - It tends to metastasize **hematogenously** to distant sites like bones and lungs, which is a key differentiator from papillary carcinoma [2]. *Hurthle cell carcinoma* - Also known as **oxyphilic follicular carcinoma**, this is considered a variant of follicular carcinoma, though sometimes classified separately. - It is **less common** than papillary or follicular carcinoma and is characterized by cells with abundant, eosinophilic, granular cytoplasm. *Medullary thyroid carcinoma* - This is a neuroendocrine tumor arising from the **parafollicular C cells** of the thyroid, which produce **calcitonin** [3], [4]. - It accounts for only about 3-5% of thyroid cancers and can be sporadic or hereditary, often associated with **MEN 2 syndromes** [3], [4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1099. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-430. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 428-429. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1102-1103.

Q: A well-differentiated follicular carcinoma of the thyroid can be best differentiated from a follicular adenoma by:

Vascular invasion. ***Vascular invasion*** - The definitive distinction between a **follicular adenoma** (benign) and a **follicular carcinoma** (malignant) is the presence of **capsular or vascular invasion** [1]. - **Vascular invasion**, specifically, indicates that tumor cells have entered blood vessels, signifying metastatic potential and malignancy [1]. *Hürthle cell change* - **Hürthle cells** (oncocytes) are characterized by abundant granular eosinophilic cytoplasm due to numerous mitochondria. - While they can be seen in both benign conditions (e.g., adenomas, Hashimoto's thyroiditis) and malignant conditions (**Hürthle cell carcinoma**, a variant of follicular carcinoma), their presence alone does not differentiate between adenoma and carcinoma. *Lining of tall columnar and cuboidal cells* - The appearance of **tall columnar and cuboidal cells** is a general histological feature seen in various thyroid conditions and is not specific for differentiating follicular adenoma from carcinoma. - While these cell types can form follicular structures, their morphology alone does not indicate malignancy or benignity without evidence of invasion [1]. *Nuclear features* - Nuclear features like **grooves**, **inclusions**, and **"orphan Annie eye" nuclei** are characteristic of **papillary thyroid carcinoma**, not typically follicular carcinoma. - Follicular carcinomas generally have bland nuclear features similar to normal follicular cells, making nuclear changes unreliable for differentiating them from follicular adenomas [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1100-1101.

Q: What is the key histological feature that differentiates follicular carcinoma from follicular adenoma of the thyroid?

Capsular invasion. ***Capsular invasion*** - **Capsular invasion** is the **classic and most commonly cited** histological criterion used to differentiate follicular carcinoma from follicular adenoma. - **Follicular adenomas** have an intact, well-defined capsule, while **follicular carcinomas** demonstrate tumor cells invading through or destroying the capsular boundary. - This is the **primary feature** taught in medical education and is easier to identify than vascular invasion. *Nuclear atypia* - **Nuclear atypia** is characteristic of **papillary thyroid carcinoma** (nuclear grooves, pseudoinclusions, ground-glass nuclei) rather than follicular lesions. - Nuclear features are **not reliable** for distinguishing follicular adenoma from carcinoma, as both can show similar nuclear morphology. - Atypia alone is insufficient to diagnose malignancy in follicular neoplasms. *Vascular invasion* - **Vascular invasion** (tumor cells within blood vessel lumens) is also a **valid diagnostic criterion** for follicular carcinoma and, when present, is sufficient for diagnosis. - Both capsular invasion and vascular invasion are **equally definitive** for diagnosing malignancy in follicular neoplasms. - However, **capsular invasion** is more commonly emphasized in teaching as the "key" differentiating feature and is more frequently encountered. *Presence of colloid* - The presence or absence of **colloid** reflects the functional activity of thyroid follicles, not malignant potential. - Both **follicular adenomas** and **follicular carcinomas** can contain abundant colloid, making this feature unreliable for differentiation.

Q: Mark the false statement regarding Hürthle cell carcinoma:

It can be diagnosed by FNAC.. ***It can be diagnosed by FNAC.*** - **Fine-needle aspiration cytology (FNAC)** alone cannot definitively diagnose Hürthle cell carcinoma because distinguishing between **benign Hürthle cell adenoma** and **malignant Hürthle cell carcinoma** requires evidence of **capsular or vascular invasion**, which cannot be assessed cytologically [1]. - FNAC results typically return as "**follicular neoplasm, Hürthle cell type**" or "**suspicious for Hürthle cell neoplasm**," necessitating surgical excision for definitive diagnosis [1]. *Arises from Hürthle cells of the thyroid.* - This statement is **true** because Hürthle cell carcinoma originates from **Hürthle cells** (also known as oxyphil cells or oncocytes), which are found in the thyroid gland. - These cells are characterized by abundant **eosinophilic, granular cytoplasm** due to a high concentration of mitochondria. *Central neck dissection is performed in certain cases.* - This statement is **true** because **central neck dissection** is considered in Hürthle cell carcinoma when there is evidence of **lymph node metastasis** or **high-risk disease features**. - While Hürthle cell carcinoma is less likely to metastasize to lymph nodes than papillary thyroid carcinoma, such an intervention may be necessary for staging and disease control. *It is not a variant of papillary thyroid cancer.* - This statement is **true** because Hürthle cell carcinoma is a distinct entity, classified as a variant of **follicular thyroid carcinoma**, not papillary thyroid carcinoma [1]. - It has a separate biological behavior and treatment strategy compared to papillary thyroid cancer. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1100-1101.

Question 1

What is the most common carcinoma of the thyroid?

Accepted Answer

Papillary thyroid carcinoma

Answer

Follicular thyroid carcinoma

Answer

Hurthle cell carcinoma

Answer

Medullary thyroid carcinoma

Question 2

A well-differentiated follicular carcinoma of the thyroid can be best differentiated from a follicular adenoma by:

Accepted Answer

Vascular invasion

Answer

Lining of tall columnar and cuboidal cells

Answer

Nuclear features

Answer

Hürthle cell change

Question 3

What is the key histological feature that differentiates follicular carcinoma from follicular adenoma of the thyroid?

Accepted Answer

Capsular invasion

Answer

Nuclear atypia

Answer

Vascular invasion

Answer

Presence of colloid

Question 4

Mark the false statement regarding Hürthle cell carcinoma:

Accepted Answer

It can be diagnosed by FNAC.

Answer

Arises from Hürthle cells of the thyroid.

Answer

Central neck dissection is performed in certain cases.

Answer

It is not a variant of papillary thyroid cancer.

Endocrine Pathology — MCQs

Endocrine Pathology — MCQs

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