MT4 and Hydrocephalus: Thus the phenotype of the MT4-MMP-null mice is likely related to a yet undetermined role for MT4-MMP in regulating thirst, which is different from the mechanisms found in hypodipsic hypernatremia seen in conditions such as intrahypothalamic hemorrhage, primary neoplasms associated with the brain (craniopharyngioma, pinealoma, meningioma), hydrocephalus, and head injuries, which are associated with abnormal vasopressin secretion [25].