FNAC is useful in all the following types of thyroid carcinoma except
**Core Concept**
Fine-needle aspiration cytology (FNAC) is a diagnostic tool used to evaluate thyroid nodules and masses. It helps identify the presence of malignancy, including various types of thyroid carcinoma. However, the utility of FNAC varies depending on the specific type of cancer.
**Why the Correct Answer is Right**
FNAC is particularly useful in diagnosing papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), and medullary thyroid carcinoma (MTC). These types of cancer often have distinct cytological features that can be identified through FNAC, such as papillary fronds in PTC and amyloid deposits in MTC. However, FNAC is not as effective in diagnosing anaplastic thyroid carcinoma (ATC), as this type of cancer often has a complex and disorganized cellular pattern that can be difficult to interpret.
**Why Each Wrong Option is Incorrect**
**Option A:** Papillary thyroid carcinoma - FNAC is actually useful in diagnosing PTC, making this option incorrect.
**Option B:** Follicular thyroid carcinoma - FNAC can also diagnose FTC, making this option incorrect.
**Option C:** Medullary thyroid carcinoma - FNAC is useful in diagnosing MTC, making this option incorrect.
**Option D:** Anaplastic thyroid carcinoma - This is the correct answer, as FNAC is not as effective in diagnosing ATC.
**Clinical Pearl / High-Yield Fact**
When interpreting FNAC results, it's essential to consider the clinical context, including the patient's age, sex, and thyroid function status. A high index of suspicion for malignancy is necessary, especially in patients with a family history of thyroid cancer or those with a history of radiation exposure.
**Correct Answer:** D. Anaplastic thyroid carcinoma.