What is the classic ultrasound appearance of a complete hydatidiform mole?

The classic ultrasound appearance of a complete hydatidiform mole is often described as a "snowstorm" pattern. This appearance is characterized by a heterogeneous mass with multiple cystic spaces and no defined embryonic structure or fetal heart activity. The "snowstorm" pattern reflects the numerous tiny vesicles or cysts that represent abnormal placental tissue, which causes the ultrasound to show a diffuse echogenic pattern similar to snow.

In contrast, other features associated with early pregnancy or different types of gestational trophoblastic disease do not exhibit this same pattern. For instance, the double decidual sac sign is typically associated with a normal intrauterine pregnancy, while a single yolk sac appearance indicates an early pregnancy but does not have the cystic, snowstorm-like characteristics of a complete mole. Oligohydramnios pertains to reduced amniotic fluid levels but does not specifically highlight the classic ultrasound characteristics seen in a complete hydatidiform mole.

Thus, the "snowstorm" appearance is key to identifying a complete hydatidiform mole on ultrasound, as it effectively differentiates it from normal pregnancy findings or other conditions.