As the complexity of hospitalized children continues to increase, hospitalists routinely encounter children with neurosurgical issues. Pediatric hospitalists must be familiar with the clinical presentation, diagnostic evaluation, and management of common pediatric neurosurgical problems. This chapter focuses on hydrocephalus and head trauma. While an increase in intracranial pressure (ICP) is a feature of both, increased ICP is primarily covered in the hydrocephalus section. Other important neurosurgical topics covered elsewhere include: Abusive Head Trauma (Chapter 40), Central Nervous System Infections (Chapter 98), and Cerebrospinal Fluid Shunt Assessment and Puncture (Chapter 188).

BACKGROUND

Hydrocephalus is the abnormal increase in cerebrospinal fluid (CSF) volume in the cranial cavity caused by a disturbance in CSF flow. Hydrocephalus is derived from the Greek term hydrokephalos, or “water on the brain.” Hydrocephalus can be acute, subacute, or chronic. Historically, hydrocephalus has been classified as obstructive (non-communicating) or communicating. In obstructive hydrocephalus, the flow is obstructed within the ventricular system or its connections to the subarachnoid space. In communicating hydrocephalus, the CSF reabsorption is impaired but flow is not obstructed. More recently, hydrocephalus has been defined as an active distension of the ventricular system of the brain related to inadequate passage of CSF from its point of production within the ventricular system to its point of absorption into the systemic circulation.¹

Pathophysiology

CSF is produced primarily by modified ependymal cells in the choroid plexus in each cerebral ventricle. CSF circulates from the pair of lateral ventricles, through the foramen of Monro to the third ventricle, then through the aqueduct of Sylvius to the fourth ventricle, and then through the paired lateral foramina of Luschka and the foramen of Magendie to the subarachnoid space, to the arachnoid granulations, and finally to the dural sinuses and into the venous drainage system for absorption (Figure 159-1). Under normal conditions, daily production should approximately equal absorption to maintain a fairly constant volume of CSF.

Mechanisms of hydrocephalus include obstructed CSF circulation, compromised absorption of CSF, or rarely, overproduction of CSF. Obstruction of CSF circulation (or non-communicating hydrocephalus) is the most common mechanism, with dilatation of the ventricular system seen proximal to the obstruction. Impaired absorption of CSF (or communicating hydrocephalus) results in dilatation of the entire ventricular system. An increased amount of CSF typically results in increased ventricular size and increased ICP.

Increased Intracranial Pressure

According to the Monro-Kellie doctrine, the brain is a closed compartment, and its internal pressure is determined by the volume of the three intracranial components: blood, CSF, and brain tissue. The pressure within the calvarium, or ICP, is typically between 8 and 12 mmHg in children. If any of the three intracranial components increase in volume, a compensatory decrease in another component must occur or ICP will rise.² Physical compression of the brain leading to a shift across the midline or herniation through the base of the skull can result in death. Therefore increased ICP is an emergency that requires immediate evaluation and management.

The classic vital sign changes associated with increased ICP are known as Cushing’s triad and include hypertension (or less commonly, widening pulse pressure), bradycardia, and respiratory irregularity (or depression). The full Cushing triad is a late sign, and may indicate impending herniation. When ICP exceeds the mean arterial blood pressure, cerebral perfusion decreases and ischemic changes begin. Ischemia activates the sympathetic nervous system, which leads to early tachycardia and an increase in blood pressure. When baroreceptors in the carotid arteries detect increased blood pressure, the parasympathetic nervous system is activated and results in bradycardia. Increased ICP may also cause mechanical distortion of the vagus nerve and the brainstem, leading to bradycardia and irregular respirations.

CLINICAL PRESENTATION

Signs and symptoms of hydrocephalus are largely due to increased ICP as a result of increased CSF volume. The time to clinical presentation is variable since hydrocephalus can be an acute or chronic process. Children can tolerate gradual increases in ICP, but most increases beyond 20 mmHg are likely to be symptomatic. Decreased level of consciousness is a reliable and worrisome sign that requires immediate evaluation and management.

Infants with hydrocephalus typically present with nonspecific findings including poor feeding, vomiting, irritability, reduced activity, lethargy, coma, or seizures. Common physical examination findings may include:

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  Vital signs: Hypertension, bradycardia, irregular respiratory rate

  
  
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  Macrocephaly (head circumference crossing percentiles in standard growth curves or head circumference greater than the 98th percentile for age)

  
  
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  Widening of sutures

  
  
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  Macewen sign (“cracked pot” sound with percussion of the head)

  
  
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  Prominent and dilated scalp veins

  
  
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  Tense, full, or bulging anterior fontanelle

  
  
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  Increased lower extremity tone or spasticity

  
  
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  Setting sun sign (downward gaze, upward eyelid retraction revealing white sclera)

Children with hydrocephalus usually present with headaches as one of the earliest symptoms. The headaches classically occur in the morning, can be variable in intensity and location, and are often associated with nausea and vomiting. Other symptoms include blurred or double vision, change in personality, drowsiness, lethargy or coma, unsteady gait, and seizures. Physical examination findings in children may include:

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  Vital signs: Hypertension, bradycardia, irregular respiratory rate

  
  
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  Stunted growth or obesity

  
  
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  Increased head size and/or frontal bossing

  
  
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  Papilledema (can take a few days to develop)

  
  
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  Cranial nerve III, IV, or VI nerve palsies

  
  
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  Ataxia

  
  
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  Hemiparesis, hyperreflexia, or hypertonia of extremities (late signs)

DIFFERENTIAL DIAGNOSIS

Hydrocephalus often presents in childhood as a result of many congenital and acquired etiologies (Table 159-1). For example, patients with myelomeningocele commonly have associated hydrocephalus from obstruction of CSF flow due to a Chiari II malformation or aqueductal stenosis.

DIAGNOSTIC EVALUATION

Neuroimaging can reveal the degree of ventricular enlargement and often the etiology of the hydrocephalus. The diagnosis can be made in certain cases by antenatal ultrasonography. In infants where the fontanelle is open (typically up to 18 months), cranial ultrasound is an appropriate imaging modality for the initial evaluation as well as a method to monitor ventricular size over time. In infants and children with suspected hydrocephalus, computerized tomography (CT) or magnetic resonance imaging (MRI) are the preferred higher resolution imaging modalities for diagnosing the cause of hydrocephalus or associated brain anomalies.³

Head CT is relatively fast, more commonly available, and does not typically require sedation. Subsequent brain MRI may be necessary to provide superior visualization of pathology, although this is often less available and may require sedation. Of note, if a diagnostic lumbar puncture (LP) is warranted in a patient with possible hydrocephalus and/or increased ICP, neuroimaging should be performed first to evaluate for a possible space-occupying lesion that could potentially result in cerebral herniation with an LP.

MANAGEMENT

In most situations, hydrocephalus will result in progressive neurologic deterioration if left untreated. Temporizing nonsurgical management, particularly in premature infants or patients too unstable for surgery, includes acetazolamide to decrease CSF production or repeated CSF removal by serial LP. Most cases of hydrocephalus require CSF shunt placement or endoscopic third ventriculostomy for long-term management of hydrocephalus.

CSF Shunts

Shunt placement is the most common treatment of both obstructive and communicating hydrocephalus to prevent accumulation of CSF. The shunt catheter typically originates in the ventricles and connects to a one-way valve system which allows CSF to drain when pressure rises in the ventricle. The shunt catheter terminates most commonly in the peritoneum or systemic circulation (right atrium) where the CSF is absorbed. (See Chapter 188 for information on CSF shunts.)

Endoscopic Third Ventriculostomy

With more recent advances in surgical techniques, endoscopic third ventriculostomy (ETV) has become an increasingly more prevalent procedure in neurosurgery. This procedure can be an alternative treatment for obstructive hydrocephalus, particularly for aqueductal stenosis, and is most successful in older children. ETV creates an outlet in the floor of the third ventricle that allows CSF to flow to the subarachnoid space, get absorbed into the superior sagittal sinus, and bypass the usual flow through the fourth ventricle (Figure 159-2).³ In certain patients, ETV can provide a long-term treatment with fewer complications than shunts. Since many cases of hydrocephalus have both obstructive and absorptive components, the onset and degree of ventricular size reduction following ETV is variable.⁴ CSF flow imaging using phase contrast MRI can determine the success of the procedure.⁵

Increased Intracranial Pressure

Increased intracranial pressure (ICP) is commonly seen in the setting of hydrocephalus. The goal of management is to minimize ICP elevation and maintain cerebral perfusion pressure to assure adequate cerebral blood flow. In a patient with signs or symptoms of increased ICP, management must begin immediately with initial stabilization. The patient should be intubated via rapid sequence intubation if the Glasgow Coma Scale ≤8 or if the patient is hypoventilating in order to maintain adequate oxygenation and ventilation, as hypercapnia causes vasodilation.

While hyperventilation can reduce ICP through cerebral vasoconstriction and reduction in cerebral blood volume, recent studies have demonstrated that it may decrease cerebral oxygenation and induce brain ischemia. Therefore prophylactic hyperventilation should be avoided in the initial phase of management, and considered only in the setting of refractory increased ICP or impending herniation.⁶ Cerebral perfusion must also be maintained with isotonic fluids to maintain euvolemia.

Given the variety of underlying causes of increased ICP (Table 159-2), management involves a variety of approaches targeting resolution of the underlying cause. Multiple temporizing measures to manage increased ICP are used including control of position, temperature, pain, agitation, seizures, and bladder drainage. The head can be elevated 15 to 30 degrees and midline to promote venous drainage. Temperatures should be kept below 38°C with antipyretics and cooling blankets because the increased metabolic demands of hyperthermia increase ICP.