Posthemorrhagic Hydrocephalus

During cerebral development, the germinal matrix is the site of intense cellular proliferation and the source of both the neuronal and glial elements of the cerebral hemispheres. Situated in the periventricular region, between the thalamus and caudate nucleus, the germinal matrix is a large structure in the early developing brain. From the end of the second trimester, it begins to involute - a process that is almost complete by about 34 weeks; therefore, germinal matrix hemorrhage is unusual after this time. The blood vessels of the germinal matrix are irregular structures that have an immature connective tissue architecture; they also lack the auto-regulatory capacity observed in mature cerebral vasculature. Both these factors are thought to contribute to the propensity for vessel rupture in the premature infant.

The incidence of germinal matrix hemorrhage shows an inverse relationship with gesta-tional age. Hemorrhage is detected in 40-45% of premature infants with birth weight less than 1500 g. In neonatal and pediatric practice, approximately 20% of infants who suffer an intraventricular hemorrhage will go on to require a shunt. Clearly, in a number of cases, the condition resolves following conservative management. The population presenting to the neurosurgeon is selection biased and hence the neurosurgical literature quotes greater rates of shunt placement. The risk of progressive hydrocephalus developing is proportional to the grade of hemorrhage.

The majority of intraventricular hemorrhages occur within the first few days after birth. In addition to prematurity, vigorous resuscitation, respiratory distress syndrome, pneumothoraces and seizures are among the factors associated with an increased risk of development of hemorrhage, with pronounced fluctuations in cerebral blood flow being the possible final pathway. Although hemorrhages may occur in the absence of clinical signs, the more extensive lesions may be associated with seizures, brady-cardias and apnoeic spells.

Germinal matrix hemorrhage is readily detected on cerebral ultrasound examination and is graded according to the site of the hematoma and the effect upon the ventricular size [4].

Once germinal matrix hemorrhage has been diagnosed, follow-up by serial ultrasound examinations is required, particularly in the

Table 24.1. Types of hydrocephalus.

Obstructive hydrocephalus

Communicating hydrocephalus

Congenital

Congenital

Aqueduct stenosis

Arnold Chiari malformation (type II, less commonly type I)

Dandy Walker cyst

Encephaloceles

Benign intracranial cysts (e.g. arachnoid cysts)

Skull base deformity

Vascular malformations (e.g. vein of Galen aneurysms)

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