**Core Concept**
Hydatidiform mole is a gestational trophoblastic disorder characterized by abnormal placental development due to failure of fertilization or abnormal chromosomal patterns. Histologically, it shows a distinctive appearance with dilated, fluid-filled spaces in the villous stroma, reflecting degenerative changes.

**Why the Correct Answer is Right**
In hydatidiform mole, the villous stroma undergoes **hydropic degeneration**, where the spaces within the villi fill with fluid, leading to a "water-filled" appearance under the microscope. This is due to abnormal trophoblastic proliferation and lack of fetal tissue. The degeneration is most prominent in the stromal component of the chorionic villi, which appears swollen and filled with clear fluid, giving the characteristic "hydatid" (water-filled) appearance.

**Why Each Wrong Option is Incorrect**
Option A: **Hyaline membrane degeneration** refers to a pathological change seen in alveolar epithelium in pneumonia, not in gestational trophoblasts. It is not a feature of hydatidiform mole.
Option C: **Non-proliferation of cytotrophoblasts** is incorrect because cytotrophoblasts are actually present and proliferate in hydatidiform mole, though they are not organized into syncytium.
Option D: **Non-proliferation of syncytiotrophoblasts** is false because syncytiotrophoblasts are hyperplastic and form large, disorganized layers, not absent.

**Clinical Pearl / High-Yield Fact**
Hydropic degeneration of the villous stroma is the hallmark histological feature of hydatidiform mole. Always look for this on histopathology when differentiating between molar pregnancy and normal pregnancy. Remember: "Hydatid" = "water-filled" villi.

✓ Correct Answer: B. Hydropic degeneration of the villous stroma