**Core Concept**
Endodermal sinus tumors (ESTs), also known as yolk sac tumors, are a type of germ cell tumor that primarily affects the gonads but can also occur in extragonadal sites. These tumors are characterized by the presence of specific histological features that are crucial for diagnosis.

**Why the Correct Answer is Right**
The correct answer is associated with the presence of Schiller-Duval bodies, which are a hallmark histological feature of endodermal sinus tumors. These structures consist of a central blood vessel surrounded by embryonic mesenchyme and covered by primitive epithelial cells. The presence of Schiller-Duval bodies is essential for the diagnosis of ESTs, as they are not typically seen in other types of germ cell tumors.

**Why Each Wrong Option is Incorrect**
**Option A:** **Psammoma bodies** are typically associated with papillary thyroid carcinoma and some types of ovarian tumors, but they are not characteristic of endodermal sinus tumors.
**Option B:** **Reed-Sternberg cells** are a hallmark of Hodgkin lymphoma, not endodermal sinus tumors.
**Option C:** **Granulosa cells** are associated with granulosa cell tumors of the ovary, which are a different type of germ cell tumor altogether.

**Clinical Pearl / High-Yield Fact**
Schiller-Duval bodies are a critical diagnostic feature of endodermal sinus tumors, and their presence should prompt further investigation into the possibility of an EST.

**Correct Answer:** C. Granulosa cells