**Core Concept**
Fine-needle aspiration cytology (FNAC) is a diagnostic tool used to obtain cell samples from superficial or easily accessible lesions, providing information about the nature of the cells. This is particularly useful in identifying benign or malignant cells, guiding further management, and reducing the need for more invasive procedures.

**Why the Correct Answer is Right**
FNAC is particularly useful in diagnosing thyroid nodules, breast lesions, and lymphadenopathy, where it can provide valuable information about cell morphology and cytological features. This helps in differentiating between benign and malignant conditions, allowing for targeted further management. The use of FNAC in these scenarios is well-established and widely accepted.

**Why Each Wrong Option is Incorrect**
**Option A:** FNAC is not typically used for diagnosing pancreatic masses, as these often require more invasive diagnostic procedures, such as endoscopic ultrasonography (EUS) or imaging-guided biopsies, to obtain sufficient tissue for accurate diagnosis.
**Option B:** FNAC is not commonly used for diagnosing central nervous system (CNS) lesions, as these often require imaging and neurosurgical interventions for diagnosis and treatment.
**Option C:** FNAC is not typically used for diagnosing gastrointestinal (GI) lesions, as these often require endoscopic biopsies or imaging-guided biopsies for accurate diagnosis.

**Clinical Pearl / High-Yield Fact**
When considering the use of FNAC, it's essential to remember that this technique is most effective for lesions that are easily accessible and have sufficient cellularity. It's also crucial to correlate FNAC results with clinical and radiological findings to ensure accurate diagnosis and guide further management.

**Correct Answer: A. Pancreatic masses**