Raised intracranial pressure

Published on 23/06/2015 by admin

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Last modified 23/06/2015

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8.2 Raised intracranial pressure

Introduction

B. Swollen contents

C. Space-occupying lesion (SOL)

D. Decreased or fixed intracranial volume

E. Pseudotumour cerebri (benign intracranial hypertension)

Most CSF is made by the choroid plexus in the lateral third and fourth ventricles. A normal child makes approximately 20 mL hr–1 and the total volume is 50 mL in an infant, rising to 150 mL in an adult. It flows through the foramen of Monro into the third ventricle, then down the aqueduct of Sylvius, which is usually only 2 mm wide, and 3 mm long in a child. This leads into the fourth ventricle and from there via the foramina of Luschka and Magendie to the basal cisterns. From there the CSF flows over the surface of the cerebellar and cerebral hemispheres to be reabsorbed through the arachnoid villi on the superior sagittal sinus. CSF can also be reabsorbed through several other channels, including a small amount through the choroid plexus and via lymphatics. Intracranial pressure will be raised whenever there is obstruction to the flow or reabsorption of CSF or in the rare circumstance where CSF production is increased.

Particular issues in children

Infants

An infant’s inability to communicate and smaller repertoire of behaviours makes raised intracranial pressure more difficult to diagnose and one needs to have a high index of suspicion as the presentation may be subtle.

The infant does not have a rigid cranial vault until fusion of the cranial sutures. This is a gradual process occurring throughout childhood; therefore ICP can cause diastasis of the cranial sutures in children, however, this is rare in children over the age of 7 years and even rarer now that computerised tomography (CT) scans and magnetic resonance imaging (MRI) allow for earlier diagnosis. Because of this flexibility, increasing intracranial contents in the infant will cause a lesser increase in the ICP and a greater increase in the head circumference than it would in older children or adults. This is one of the reasons why acute increases in ICP in infants are often not easily detected by the infant’s subtle change in behaviour patterns.

The measurement of head circumference (occipitofrontal) is a useful means of detecting intracranial pathology. The head circumference should be plotted on centile charts, using prior measurements, if available, to determine if there has been a trend to cross percentiles. The child’s length and weight should be plotted concurrently, to evaluate if the head is disproportionately large or small. When the cranial sutures separate due to expansion, percussion of the skull makes a sound similar to that of a ‘cracked pot’. This is known as Macewen’s sign.

Conversely, the open anterior fontanelle allows direct palpation of intracranial pressure up to the age of 9 to 18 months. It is highly recommended that one closely observes the fontanelles of normal infants, to help one identify abnormalities in clinical practice. The normal fontanelle will bulge slightly when the infant is lying down. It will become depressed when the child is sat up. It will bulge more prominently when the infant is crying or straining. The normal fontanelle will have an arterial pulsation more apparent when the infant is upright.

The fontanelle also provides access for emergency procedures such as the draining of a traumatic subdural or a ventricular tap. Fortunately the need for these procedures in the emergency department (ED) rarely arises. When it does, however, it should be done by a neurosurgical specialist (or trainee if sufficiently experienced). In centres where such help is not rapidly available, over-the-phone advice from a neurosurgeon may help with both the decision to do the procedure and the technique.

Clinical features of raised intracranial pressure

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