**Core Concept**
Follicular carcinoma of the thyroid is a type of malignant tumor that originates from the follicular cells of the thyroid gland. It is characterized by its ability to metastasize through the bloodstream, which sets it apart from other types of thyroid cancer.

**Why the Correct Answer is Right**
Follicular carcinoma of the thyroid is known to spread through the hematogenous route, meaning it travels through the bloodstream to reach distant organs such as the lungs and bones. This is in contrast to papillary thyroid carcinoma, which tends to spread through lymphatic vessels. The unique behavior of follicular carcinoma is due to its ability to invade blood vessels and release cancer cells into the circulation. This characteristic makes early detection and treatment crucial in preventing the spread of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Follicular carcinoma is not the most common type of thyroid cancer. Papillary thyroid carcinoma is the most common type, accounting for approximately 70-80% of all thyroid cancer cases.
**Option B:** Follicular carcinoma is not readily diagnosed by fine-needle aspiration cytology (FNAC). Due to its similar cytological features to benign follicular lesions, FNAC may not be sufficient for a definitive diagnosis. A histopathological examination of the tumor is often required for a definitive diagnosis.
**Option D:** Follicular carcinoma is not typically seen as multifocal. While it can occur as a multifocal tumor, it is more commonly seen as a unifocal tumor, originating from a single site within the thyroid gland.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the diagnosis of follicular carcinoma requires a combination of clinical, radiological, and pathological findings. A thorough evaluation, including histopathological examination, is necessary to distinguish it from other thyroid lesions.

**✓ Correct Answer: C. More commonly spreads through hematogenous route**