AVP and Hydrocephalus: SIADH aetiology includes: malignancies (small cell lung cancer and others) with direct AVP secretion by tumour cells [4, 5], central nervous system disorders (cerebral infections, trauma, hydrocephalus) disrupting hypothalamic–pituitary function [6], pulmonary diseases affecting osmoreceptors or triggering AVP release through inflammatory pathways [7], medications (SSRIs [selective serotonin reuptake inhibitors], carbamazepine) [8] and genetic disorders [9].