Pituitary stalk block syndrome (PSIS), also known as pituitary stalk transection syndrome, is a series of clinical syndromes caused by various causes of pituitary stalk agenesis or thinning and ectopic posterior pituitary lobes, resulting in the inability of hormones secreted by the hypothalamus to be delivered to the normal posterior pituitary lobes through the pituitary stalk and to act on the anterior pituitary lobes through the pituitary portal system. There are currently two hypotheses for the mechanism of PSIS development. The first one suggests that PSIS is an acquired injury due to neonatal hypoxia, as PSIS is highly correlated with breech prematurity and cesarean delivery. However, due to the high incidence of concomitant CNS malformations, such as ocular agenesis, microcephaly, Chiari malformation, optic septal dysplasia, and corpus callosum hypoplasia, these are not consistent with the theory of trauma. So another explanation is thought to be due to failure of normal evoked behaviors during pituitary organogenesis, while the high incidence of breech prematurity is thought to be due to hypotonia of the uterus due to hormonal deficiency.