Intraventricular iron causes severe hydrocephalus – a model of severe neonatal hydrocephalus

Neonatal germinal matrix hemorrhage-intraventricular hemorrhage and subsequent post-hemorrhagic hydrocephalus (PHH) is a leading cause of neurologic morbidity and mortality in preterm infants. Preclinical models of PHH have implicated hemoglobin and iron-mediated cellular injury in the pathogenesis of PHH, but have typically demonstrated a phenotype characterized by mild to moderate ventriculomegaly – the equivalent of which may not even require intervention in the human condition. We sought to establish a preclinical model of severe IVH that recapitulates the severity of the hydrocephalus phenotype requiring neurosurgical intervention and to determine the causal blood degradation product resulting in severe hydrocephalus following preterm IVH. Sterile saline 7.5 µL/g (n = 20), hemoglobin (Hb) 120 mg/mL (n = 25), iron 1.2 mg/mL (FeCl3) (n = 49), or lysed red blood cells (RBC) 7.5 µL/g (n = 41) were injected bilaterally into the lateral ventricles of postnatal day 3 Sprague Dawley rat pups. Ventricular volumes were assessed at postnatal days 5, 12, 19 and 26 with 11.7 T MRI and compared between groups. Ventricular ependyma and choroid plexus morphology were characterized with SEM. Ependymal and choroid plexus iron deposition were evaluated with Perls stain. Clinical and behavioral manifestations of hydrocephalus were monitored. Lysed RBC and iron intraventricular injections resulted in severe hydrocephalus characterized by marked ventriculomegaly and domed cranium. Very severely affected hydrocephalic pups exhibited poor weight gain and early death. The control (saline) and Hb-injected pups did not demonstrate hydrocephalus phenotype or significant ventricular enlargement at any postnatal days from Day 5 to Day 26. While ventricular volumes at Day 26 were markedly enlarged in iron- and lysed RBC-injected rat pups compared to saline- and hemoglobin-injected rat pups (p < 0.0001), ventriculomegaly was most severe in the iron-injected rat pups. Ependymal and choroid plexus iron deposition (Perls stain) was significantly increased in iron- (p < 0.0001) and lysed RBC-injected pups (p = 0.024) with hydrocephalus when compared to that in saline-injected pups. SEM revealed denuding of the ependymal cilia and morphologic changes in the choroid plexus of iron- and lysed RBC-injected pups with hydrocephalus. Intraventricular free iron is critical to the development of PHH following IVH in neonatal rats, while intraventricular Hb did not cause hydrocephalus. PHH is characterized by morphologic changes to the ventricular ependymal cilia and choroid plexus reflecting iron-mediated cellular injury.