Wednesday, April 20, 2011

Posthemorrhagic Hydrocephalus of Prematurity

The most common cause of hydrocephalus in the premature infant is a germinal matrix hemorrhage. The germinal matrix is a very vascular area in the fetal brain, in the subependymal region located at the level of the foramen of Monro. It is from the very thinwalled germinal matrix vessels that the bleeding is thought to occur in preterm infants. Bleeding can spread, most often to the adjacent ventricles and into the surrounding parenchyma. The germinal matrix gradually involutes after 34 weeks gestation and nearly disappears by 40 weeks. A grading system has been devised to describe the severity of the bleeding – grades I–IV.
Premature infants of less than 34 weeks gestation with very low birth weight (<1500 g) are at greatest risk for developing IVH. With current management, 20% of these preterm infants will develop an IVH. The risk of developing posthemorrhagic hydrocephalus (PHH) is related directly to the extent of the hemorrhage. Hydrocephalus develops in 20–74% of infants with IVH [3]. Infants with a grade I or II bleed do not have hydrocephalus by definition; 55% of infants with a grade III hemorrhage and 80% of those with a grade IV bleed develop hydrocephalus. PHH may develop as a result of the accumulation of blood and hemorrhagic debris within the ventricles and subarachnoid spaces. Obstruction of the aqueduct of Sylvius or foramen of Monro may occur. The breakdown of blood may also render the arachnoid villi unable to reabsorb the CSF. Multiloculated hydrocephalus may occur after IVH due to ventriculitis. Ventricular septations develop causing isolated compartments of fluid within the ventricles.
Many premature infants require surgical intervention to treat the hydrocephalus until it is resolved. About 20–30% will require permanent shunting.

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