Normal physiology

Normal intracranial pressure (ICP) is 6–18 cmH₂O. It is the product of the intracranial contents mainly blood, brain and cerebrospinal fluid (CSF) and the resistance of the cranial vault. Normal ICP has a diurnal cycle that is higher in the early hours of the morning when one is normally supine during sleep. Therefore the symptoms of raised ICP, such as headache and vomiting, are usually worse in the morning. Intracranial pressure may be raised by anything that can cause an increase in the volume of its contents or a decrease in the size of the cranial cavity (Table 8.2.1). This section will not cover the diagnosis and management of raised intracranial pressure associated with trauma. Those issues are covered in Chapter 3.2.

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.

The central herniation syndrome

Generalised midline or bilateral swelling above the tentorium cerebelli causes the midbrain to herniate through the tentorium. This leads to dysfunction of the midbrain and higher centres due to compression, causing:

The lateral mass herniation syndrome

A unilateral supratentorial swelling will give rise to a pattern of events formerly known as the uncal herniation syndrome. Imaging studies now show that herniation of the uncus happens very late in the process and is not responsible for most of the signs. Features in approximate sequence are:

Cerebellar tonsillar herniation syndrome

A wide variety of signs and symptoms arise from posterior fossa masses. However, sometimes as the cerebellar tonsils are pushed through the foramen magnum and the medulla with its respiratory control centres is compressed, the following sequence occurs:

General observation

In the unco-operative irritable child, general observation from a distance is a vital part of the examination. It may reveal a large and/or an asymmetric head, evidence of trauma, gait, speech or visual disturbance. Watching a playful child from a distance will yield a lot more useful neurological information than an attempted formal examination of a screaming unhappy one.

Fundi

Although often difficult to visualise in children, fundal examination is of vital importance. Using a parent as a visual distraction will often help. With patience, the disc can usually be visualised through an undilated pupil. One may be able to visualise retinal venous pulsations. The implication of these pulsations is that intracranial pressure is less than peak venous pressure. Papilloedema is less common in infants with raised ICP due to the ‘decompressing’ presence of an open anterior fontanelle. Examination of the fundi is less useful in acute severe raised ICP, as papilloedema takes days to evolve. Other retinal findings associated with raised ICP include retinal haemorrhages, which have a strong association with non-accidental injury, aneurysms and arteriovenous malformation that may be associated with similar intracranial lesions, and subhyaloid haemorrhages which may be seen in patients with subarachnoid haemorrhages. In some instances it may be useful to ask an ophthalmologist to examine the child through dilated pupils.

Peripheral neurological signs

The development of ‘handedness’ is not apparent in normal infants under 1 year of age. If handedness is apparent in infancy, it is usually due to a neurological or musculoskeletal lesion, some of which are associated with raised ICP. Hydrocephalus may produce lower limb signs with gait disturbance in the ambulant child. In infants, this may be apparent when the child is held up by hands around the chest with the legs suspended in midair. Spasm of the adductors will cause scissoring of the lower limbs.

Management of raised ICP

Acute severe increases in ICP are a true emergency and children with features of the herniation syndromes should be treated in the resuscitation area of the ED or the neurosurgical operating theatre. A neurosurgeon should be consulted as early as possible.

In this situation efforts should be directed towards maintaining cerebral oxygenation and perfusion by supporting the child’s ventilation and circulation, if necessary using rapid sequence intubation (RSI) and mechanical ventilation. Some drugs used in RSI and the manipulation of the airway itself may cause a further transient rise in intracranial pressure. Several strategies have been used to avoid this transient rise including administering an IV dose of lignocaine just prior to RSI and giving a ‘defasciculating’ dose of a non depolarising neuromuscular blocking agent just before the Succinylcholine. There are no studies looking at what effect the use of these strategies has on patient outcome. This author?s opinion is that it is more important to avoid hypotension and hypoxia during RSI because there is strong evidence that these are harmful. Therefore this author does not use these strategies because it is a change in the usual practice of the department which more likely to lead to errors and delays in the RSI process. (See the end of the chapter for further reading on this issue). Intracranial pressure can be reduced by giving intravenous mannitol 1 g kg^–1 and nursing the patient in a 30° head up position. Mannitol should not be given if the patient has circulatory failure (i.e. hypotension or hypoperfusion) as the osmotic diuresis that it causes could exacerbate the hypoperfusion. Just as in trauma so in medical illnesses C (circulation) comes before D (disability) meaning that a perfusing blood pressure must be maintained if there is to be any cerebral perfusion pressure. There is strong evidence against prolonged hyperventilation because vasoconstriction impairs cerebral perfusion despite the reduction in intracranial pressure. pCO₂ should be kept between 35 and 40 mmHg unless the above measures have been unsuccessful or herniation is progressing, in which case the pCO₂ can be taken down to 25 mmHg for a brief period while further measures are commenced. Whilst these measures are taking effect consideration and management of the underlying cause should be undertaken. This will be aided by a concise history and some rapid bedside testing such as blood gas, which may reveal conditions such as hyponatraemia or any infusions containing free water. If an infant in this situation does not respond to these measures, a neurosurgeon should be urgently consulted regarding a ventricular or subdural tap via the open fontanelle. In older children who do not respond adequately, the options depend on the clinical situation and the underlying cause. Therapeutic options include: consulting neurosurgeons and getting an urgent CT scan; palliating or treating an underlying cause urgently (e.g. high-dose dexamethasone for vasogenic oedema or hypertonic saline for hyponatraemia); or maintaining cerebral perfusion pressure by maintaining mean arterial blood pressure at above normal levels with fluids and inotropes and reducing cerebral metabolic demand with drugs such as thiopentone. Other neurosurgical interventions include: craniotomy; insertion of external ventricular drain; and insertion of a CSF reservoir or a complete CSF shunt. Where a shunt is already present this may be tapped (see Chapter 8.1 on shunt complications). Consideration should also be given to prophylactic anticonvulsants because seizure will cause a further acute rise in ICP. Once initial stabilisation is underway and neurosurgeons are involved referral to a paediatric ICU is mandatory.

Children with less severely raised ICP usually need investigation and treatment of the cause, usually under the care of paediatric neurosurgeon whilst avoiding interventions that may increase ICP. One should avoid the infusion of hypotonic fluids for a vomiting child or the administration of certain drugs. Children with hydrocephalus will usually require admission for consideration of a shunt, or 3rd ventriculostomy.

Iatrogenic

Any child receiving intravenous fluids, especially for treatment of diabetic ketoacidosis (DKA), who develops headache and/or drowsiness and/or seizures during therapy should be considered to have raised ICP until proven otherwise. A thorough assessment should be made and electrolytes checked for disturbances that may lead to cerebral oedema. Imaging should be considered. If cerebral oedema is confirmed or not excluded then the child should be treated as above and observed in a paediatric intensive care unit.

Pseudotumour cerebri (PTC or benign intracranial pressure)

This condition is characterised by sustained raised ICP causing symptoms similar to a cerebral tumour but with no anatomical abnormality on neuroimaging. It is usually due to decreased CSF re-absorption. PTC has many causes (Table 8.2.2). It is more prone to occur in overweight pubescent girls, in whom no cause is found. The presentation is usually with headaches and vomiting, which are worse in the morning. Some patients may complain of transient visual obscuration with blurring or darkening of vision that lasts less than 30 seconds. Later there may be unilateral or bilateral 6th nerve palsies causing diplopia on lateral gaze. Papilloedema is often the only positive physical finding. The most significant complication of PTC is loss of vision. This begins with an enlargement of the blindspot associated with papilloedema, and later progresses with erosion of the peripheral visual fields. Left untreated the patient with persistent PTC will eventually develop optic atrophy and blindness.