The prenatal examination of the placenta is often an afterthought to that of the fetus in ultrasonography. Not giving the placenta its due may however result in potentially serious placental pathologies remaining undiscovered, notably in the presence of anechoic zones. These latter have earned numerous names, including "placental lakes", "placental venous lakes", "placental lacunae" or "placental caverns" among others, but they have received little attention in the literature. We thus feel that it is essential to review the various pathologies that placental lakes may signal, since any one of them may greatly affect patient management. The difficulty resides in the diversity of these pathologies, sometimes oncological, other times fetal, and in the potential need for multidisciplinary surgery. Some of these causes of placental lakes may result in maternal or fetal complications and/or necessitate increased and casespecific surveillance. The diagnosis and treatment of such cases requires close collaboration between sonographers, obstetricians, geneticists and pathologists. The work we present here focuses on the different etiologies to consider in the presence of a lacunar placenta and the necessary diagnostic measures. Our objective is to propose a diagnostic flowchart to aid clinicians in this dense differential diagnosis.