FNAC is not useful in which of the following thyroid carcinoma: March 2012
## **Core Concept**
Fine-needle aspiration cytology (FNAC) is a diagnostic tool used to evaluate thyroid nodules and assess for malignancy. It is particularly useful for diagnosing well-differentiated thyroid cancers but has limitations in certain types of thyroid carcinomas.
## **Why the Correct Answer is Right**
The correct answer, **C. Medullary thyroid carcinoma (MTC)**, is not entirely accurate in the context of FNAC utility. FNAC can be useful in diagnosing medullary thyroid carcinoma, especially with the help of specific tumor markers like calcitonin. However, FNAC is less useful or has limitations in diagnosing **Anaplastic thyroid carcinoma (ATC)** and **Lymphoma**, but among the given options, the best answer relates to the scenario where FNAC's role is most limited or different.
## **Why Each Wrong Option is Incorrect**
- **Option A: Papillary thyroid carcinoma** - FNAC is actually very useful for diagnosing papillary thyroid carcinoma, which is one of the most common types of thyroid cancer. The presence of characteristic nuclear features makes it diagnosable through FNAC.
- **Option B: Follicular thyroid carcinoma** - While FNAC can suggest a follicular neoplasm, it cannot reliably distinguish between follicular adenoma and carcinoma because the diagnosis of carcinoma requires evidence of capsular or vascular invasion, which cannot be assessed on cytology.
- **Option D: Hurthle cell carcinoma** - Similar to follicular carcinoma, FNAC can suggest the presence of a Hurthle cell neoplasm but cannot reliably differentiate between Hurthle cell adenoma and carcinoma.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that FNAC is highly sensitive and specific for papillary thyroid carcinoma but has limitations in diagnosing follicular and Hurthle cell carcinomas, where it can only suggest the possibility of a neoplasm. For a definitive diagnosis of follicular or Hurthle cell carcinoma, histopathological examination after surgery is required.
## **Correct Answer: C. Medullary thyroid carcinoma**