INI-CET 2025 — Internal Medicine

Question 31: Multiple lytic lesions on skull are seen in which thyroid carcinoma?

• A. Follicular carcinoma (Correct Answer)
• B. Thyroid lymphoma
• C. Papillary carcinoma thyroid
• D. Hurthle cell carcinoma

Explanation: ***Follicular carcinoma*** - Follicular thyroid carcinoma (FTC) classically spreads hematogenously to distant sites, most commonly the **bone (skull, spine, pelvis)** and lungs. - Bone metastases, especially in the skull, are typically **lytic** and may present as solitary or multiple lesions with a characteristic **"cannonball" appearance** on imaging if involving the lungs. ***Papillary carcinoma thyroid*** - Papillary thyroid carcinoma (PTC) predominantly spreads locally via **lymphatics** to regional neck lymph nodes, rarely causing distant metastases early in the disease course. - Distant metastases, when they occur, are usually to the lungs (small micronodules) and are less common as lytic skull lesions compared to FTC. ***Hurthle cell carcinoma*** - Hurthle cell carcinoma (a variant of follicular carcinoma) also has a high propensity for **hematogenous spread** to bone and lung. - While it can cause lytic bone lesions, it is best classified under the broader category of follicular carcinoma for its metastatic pattern, but FTC is the most common association for lytic skull lesions among the choices. ***Thyroid lymphoma*** - Thyroid lymphoma is rare and usually presents as a **rapidly enlarging thyroid mass** in an older patient, often associated with a background of Hashimoto's thyroiditis. - It typically causes diffuse thyroid involvement and local invasion into the neck structures; distant metastases, especially lytic skull lesions, are highly **uncommon**.