ABSTRACT
Acrania is a fetal malformation characterized by complete or partial absence of the calvaria above the orbits and supraciliary ridge. No exact mechanism is demonstrated for this anomaly but disturbances in mesenchymal migration during the fourth week of development are the most documented. The key sonographic features of acrania are absent calvaria and dorsally bulging brain (Mickey Mouse head). Due to the normal process of ossification of cranial bones, the diagnosis can be established only after 11 weeks of gestation. Early detection is extremely important. The prognosis is extremely poor so elective termination of pregnancy is the treatment of choice. In this paper, we discuss the things we know about pathogeny and ultrasonographic features of fetal cranial malformations based on a case diagnosed late during gestation.