Hydrocephalus in infants: the unique biomechanics and why they matter.

Abstract

Hydrocephalus diagnosed prenatally or in infancy differs substantially from hydrocephalus that develops later in life. The purpose of this review is to explore hydrocephalus that begins before skull closure and full development of the brain. Understanding the unique biomechanics of hydrocephalus beginning very early in life is essential to explain two poorly understood and controversial issues. The first is why is endoscopic third ventriculostomy (ETV) less likely to be successful in premature babies and in infants? The second relates to shunt failure in a subset of older patients treated in infancy leading to life-threatening intracranial pressure without increase in ventricular volume. The review will utilize engineering concepts related to ventricular volume regulation to explain the unique nature of hydrocephalus developing in the fetus and infant. Based on these concepts, their application to the treatment of complex issues of hydrocephalus management, and a review of the literature, it is possible to assess treatment strategies specific to the infant or former infant with hydrocephalus-related issues throughout life. Based on engineering, all hydrocephalus, except in choroid plexus tumors or hyperplasia, relates to restriction of the flow of cerebrospinal fluid (CSF). Hydrocephalus develops when there is a pressure difference from the ventricles and a space exterior to the brain. When the intracranial volume is fixed due to a mature skull, that difference is between the ventricle and the cortical subarachnoid space. Due to the distensibility of the skull, hydrocephalus in infants may develop due to failure of the terminal absorption of CSF. The discussion of specific surgical treatments based on biomechanical concepts discussed here has not been specifically validated by prospective trials. The rare nature of the issues discussed and the need to follow the patients for decades make this quite difficult. A prospective registry would be helpful in the validation of surgical recommendations. The time of first intervention for treatment of hydrocephalus is an important part of the history. Treatment strategies should be based on the assessment of the roll of trans-mantle pressure differences in deciding treatment strategies. Following skull closure distension of the ventricles at the time of shunt failure requires a pressure differential between the ventricles and the cortical subarachnoid space.