**Core Concept**
Hurthle cell tumors are a type of thyroid neoplasm characterized by the presence of cells with abundant eosinophilic, granular cytoplasm. These cells are derived from follicular epithelial cells and are often associated with autoimmune thyroiditis.

**Why the Correct Answer is Right**
Hurthle cell tumors are typically benign, but they can be malignant in a small percentage of cases. They are often seen in patients with Hashimoto's thyroiditis, a chronic autoimmune condition that leads to inflammation and fibrosis of the thyroid gland. The pathogenesis of Hurthle cell tumors is thought to be related to genetic mutations that activate the PI3K/AKT signaling pathway, leading to cell proliferation and survival.

**Why Each Wrong Option is Incorrect**
**Option A:** Hurthle cell tumors are not a type of medullary thyroid carcinoma, which is a distinct entity that originates from parafollicular cells.
**Option B:** Hurthle cell tumors are not typically associated with familial adenomatous polyposis (FAP), a genetic disorder that increases the risk of colorectal cancer and other tumors.
**Option C:** Hurthle cell tumors are not a type of anaplastic thyroid carcinoma, which is a highly aggressive and malignant form of thyroid cancer.

**Clinical Pearl / High-Yield Fact**
Hurthle cell tumors are often difficult to distinguish from other types of thyroid neoplasms, and a definitive diagnosis typically requires histopathological examination. It is essential for clinicians to be aware of the clinical and histological features of Hurthle cell tumors to ensure accurate diagnosis and management.

**Correct Answer: D. Hurthle cell tumors are a type of follicular thyroid neoplasm characterized by cells with abundant eosinophilic, granular cytoplasm.**