Placental function is essential for fetal growth and wellbeing.
Although uncommon, abnormalities of the placenta are important to recognize owing to the potential for maternal and fetal morbidity and mortality.
Sonography is the imaging modality of choice for placental evaluation.
On the other hand, by increasing placental age, this structure becomes nonhomogeneous by itself.
There are some pathological conditions  which cause placental heterogeneity and produce some hypoechoic zones in placenta. Placental Lakes, Sub chorionic Fibrin Deposition, and placental Infarcts are examples of hypoechoic zones in placenta becoming obvious with placental maturity.
The role of radiologist is to define pathological conditions from physiologic ones.