In one of the authors’ previous 4-year experience at a tertiary institution with a busy pediatric neurosurgery service, a third of all procedures (950/2948) were dedicated to the treatment of hydrocephalus. Hydrocephalus also serves as a platform for the discussion of neuroanatomy and intracranial pressure (ICP) as foundational information for other topics later in this chapter.

Cerebrospinal fluid (CSF) is produced constantly. The volume produced is proportional to the size of the brain and the patient, being less in infants compared with older children. Regardless, the volume is substantial for any age or size. By the age of 5 years, the brain has already achieved 90% of the adult size. In the full-sized or near-full-sized brain, CSF production averages approximately 20 mL/h or 480 mL/day. Few specific disease states can increase or decrease the amount of CSF produced. Under normal circumstances, the majority of CSF is produced by the choroid plexus within the ventricular system. However, the brain can still produce approximately a third of CSF via bulk flow. This bulk flow is thought to be extracellular fluid within the brain parenchyma that moves centripetally toward the ventricular system. Removing the choroid plexus therefore cannot eliminate CSF production. An adult human with normal neuroanatomy harbors approximately 150 mL of CSF within the ventricles and intraspinal and intracranial subarachnoid spaces. Daily production equates to more than three times the static volume of CSF. The process of CSF reabsorption is dependent on a pressure gradient across the subarachnoid space into the venous system via the arachnoid granulations. The failure to circulate or absorb even a small percentage of the CSF produced can cause problems of ventricular distention and/or raised ICP. Obstruction within the ventricular system, its outlets, or the subarachnoid cisterns or a failure of absorption into the venous system can lead to ventricular distention and/or enlarged subarachnoid spaces. Likewise, elevated central venous pressures that can be seen in some congenital heart conditions, as well as jugular venous obstruction, can lead to a compensatory rise in ICP.

Causes of hydrocephalus can be divided into congenital and acquired. Common congenital causes of hydrocephalus include aqueductal stenosis and myelomeningoceles. Acquired causes are typically intraventricular hemorrhage (most often in premature neonates), postinfectious, posttraumatic, and from brain tumors.

An infant with raised ICP may present with a history of irritability, emesis, poor feeding, failure to thrive, and lethargy. In addition, older children may present with complaints of headache, visual disturbance, loss of developmental milestones, impaired academic performance, and clumsiness. Hydrocephalus is rarely a cause of seizures, and a seizure in a child with raised ICP may actually be posturing (flexor or extensor) from impending herniation. Posturing from raised ICP is an urgent matter. Although epilepsy commonly coexists in children with hydrocephalus, seizure activity is rarely caused by hydrocephalus. Hence, it is important to get a very clear history as to what was being called a “seizure” in these children.

On examination of the infant, the occipital-frontal circumference (OFC), character of the fontanelle, separation of the cranial sutures, scalp vein distention, eye position, heart rate, blood pressure, and respiratory rate are important factors to assess. As a rule of thumb, in the neonatal setting, OFC growth greater than a centimeter per week serves as a possible indication of raised ICP in the neonate. Plotting the child’s OFC on a growth chart, corrected for prematurity as necessary, can be helpful. In the infant with hydrocephalus, the fontanelle may not be “tight” or “bulging” as the compliant skull readily gives way to elevated ICP. That is why palpation of the cranial sutures, particularly the coronal suture, is important to assess for separation of the frontal and parietal bones as a sign of raised ICP. Prominence of scalp veins can serve as a possible indication of elevated ICP. “Sun-setting” eyes with lid retraction is a downward deviation of the eyes with impaired upward gaze ( Fig. 18.1 ). The upper sclera becomes unnaturally visible and is a sign of elevated ICP or midbrain abnormality. Esotropia, medial deviation of one or both eyes because of weakness in the abductor muscle, supplied by the abducens nerve, also can be a sign of raised ICP. Elevated ICP can cause vital sign changes referred to as Cushing triad: bradycardia, hypertension, and irregular respirations. In the hospital setting, trends of any one vital sign such as a slowing heart rate, an increasing blood pressure, or a reduced respiratory rate can signal a possible elevation in ICP. The whole triad does not need to be present when ICP is elevated.

Infant with hydrocephalus and “sun-setting” eyes. There is downward deviation of the eyes, and the upper sclerae are unnaturally visible.

A more in-depth examination is possible in an older child. Except for the fontanelle and cranial suture examination, many of the same signs are looked for when examining a child beyond infancy. In addition, a funduscopic examination may be possible to look for papilledema or optic pallor. If the child is cooperative, tests of memory, coordination, balance, and gait are helpful in trying to detect impaired brain function from elevated ICP.

Cranial imaging of the child with possible hydrocephalus can involve plain radiographs, ultrasound (US), computerized tomography (CT), and magnetic resonance imaging (MRI) ( Fig. 18.2A ). Plain radiographs are not recommended but may show the effects of chronically elevated ICP on the inner table of the skull causing a “copper beaten” appearance. An open fontanelle is required for cranial US. The US can nicely visualize the lateral ventricles, but the extraaxial spaces and the posterior fossa contents, as well as the fourth ventricle, are usually incompletely viewed. US can be performed at the bedside without the need for transport or sedation, features that make it indispensable in the neonatal intensive care unit (NICU). A cranial CT gives more information with very good visualization of all ventricles, the extraaxial spaces, and skull anatomy. Although a CT is fast and rarely requires sedation of the child, radiation is a necessary component of the examination. MRI provides much more exquisite detail of the brain anatomy but shows the skull anatomy and shunt components less well than CT. MRI sequences that take only a few minutes have been developed to simply assess the ventricular anatomy in the setting of known hydrocephalus to avoid or minimize sedation; however, there remains a higher likelihood of the need for sedation and reduced patient access when compared with CT.

(A and B) T2-weighted MRI of 5-month-old infant with untreated congenital hydrocephalus due to aqueductal stenosis. Note the enlarged lateral ( arrowheads ) and third ( diamond ) ventricles. The fourth ventricle ( asterisk ) is normal sized, and the obstruction is at the aqueduct ( white arrow ). (C) 5 months after surgery from VP shunt placement showing decompressed ventricles ( black arrow ).

Endoscopic third ventriculostomy (ETV) with or without choroid plexus coagulation has increasingly been utilized in recent years and serves a role in select patient populations, though the mainstay of treatment for hydrocephalus remains the ventriculoperitoneal shunt (VPS) (see Fig. 18.2B ). It is not within the scope of this chapter to discuss the indications for ETV versus shunt placement. However, the general concept of a proximal intracranial or spinal catheter diverting fluid to a distal location for reabsorption holds true for all neurosurgical shunts. These terminal locations most commonly include the peritoneum, pleural space, subgaleal space, and venous system (right atrium–caval junction). Rarely the gallbladder or another terminal space is needed, and many times it prompts the assistance of a pediatric general surgeon. Pediatric general surgeons or interventional radiologists are usually involved in placement of a ventriculoatrial shunt.

An occasional clinical scenario is the timing of gastrostomy and VPS placement in the premature intraventricular hemorrhage NICU population, as well as some children with malignant tumors in whom either the neurologic sequela or the chemotherapy impede adequate nutritional intake. Published studies have been inconsistent at defining the risks of either gastrostomy causing a shunt infection or the increased risk of shunt infection in the setting of gastrostomy. ^, When possible, we temporally separate VPS and gastrostomy placement.

Although most neurosurgeons place the peritoneal end of the VPS without general surgical assistance, general surgical expertise may be requested for peritoneal access or assistance in certain situations : extreme obesity, revision with extensive intraabdominal scarring/intraperitoneal adhesions, suspected bowel injury, or for removal of intraperitoneal catheters that are either fractured and free floating or intensely scarred to intraperitoneal structures (often in the setting of infection). Erosion of distal catheters through the bowel wall has almost disappeared as a complication since abandoning use of catheters reinforced with a spiral wire that made them particularly stiff.

Final mention should be made regarding common general, urologic, and pelvic surgeries and VPSs. There is a paucity of literature regarding shunt infection risk. Clean and clean-contaminated wounds for both laparoscopic and open surgery are thought to carry very low risk for shunt infection. Contaminated/dirty wounds require intraoperative neurosurgical consultation and likely shunt externalization. Lastly, maintenance of VPS flow has been proven to occur against standard laparoscopic insufflation pressures for abdominal surgery.

Although a VPS is by far the device most frequently implanted by pediatric neurosurgeons, other common implants include intrathecal baclofen pumps, vagal nerve stimulators (VNSs), and deep brain stimulators (DBSs). Because these devices are often present in children with medically complex problems, an understanding of their components is important to avoid device damage and adverse clinical events.

The intrathecal baclofen pump is a programmable pump that delivers baclofen, a γ-aminobutyric acid agonist, directly into the CSF. This is primarily used in children with quadriparetic spasticity with the goals of occasionally increasing function, but more often to make the care of the child easier and reduce discomfort. The pump is about the size of a hockey puck, and it is sizable and protuberant in children with minimal subcutaneous tissue. Pumps are most commonly implanted in the subcutaneous or subfascial compartment of the abdominal wall ( Fig. 18.3 ). The catheter then runs laterally around the flank to enter the spinal subarachnoid space through a posterior midline incision. The side to which the tubing courses around the flank is often intuitive, but some devices are deceivingly in the midline of the abdominal wall. Reviewing previous radiographs before any planned abdominal, retroperitoneal, or spinal intervention is important to avoid catheter damage and subsequent medication withdrawal. Baclofen withdrawal is a life-threatening condition marked by hyperpyrexia, seizures, cardiovascular collapse, and coma.

This lateral radiograph depicts an implanted baclofen pump ( white arrow ) and catheter entering the spinal subarachnoid space ( black arrow ).

A VNS consists of a generator and wire electrodes. These devices are used in patients with medically refractory epilepsy in whom a surgical resection is not thought to be helpful. Via a dissection of the carotid sheath, the electrodes are almost always placed on the left vagus nerve. Avoidance of the right vagus nerve is due to the higher parasympathetic cardiac efferents of that side ( Fig. 18.4 ). The generator often resides in the subcutaneous space below the ipsilateral clavicle. Rarely, some conditions may warrant placement of the generator elsewhere. The electrodes and the insulation are quite fragile to needle sticks, sharp dissection, and monopolar electrocautery. In these children, central venous access should always be right sided if needed.

A vagal nerve stimulator ( horizontal arrow ) is seen on the left anterior chest wall, and the electrodes ( vertical arrow ) have been attached to the left vagus nerve between the carotid artery and internal jugular vein. The patient also has scoliosis spinal instrumentation.

The DBS is similar to the VNS except that the electrodes enter the brain via a frontal approach and then travel retroauricular to the neck/chest. These devices can be placed unilaterally or bilaterally. The purpose of these devices is to treat severe movement disorders, most often dystonia. Since the generators often reside in the subcutaneous subclavicular space with electrodes coursing superiorly to the cranium, any interventions in the subclavicular or anterior neck should be performed on the contralateral side if possible. If this is not possible, radiographs should be obtained to be certain of the electrode course and all efforts made to avoid damage or contamination.

Lastly, monopolar electrocautery has variable safety in the presence of shunts, pumps, and generators. Bipolar is safe in all devices, so long as direct cauterization of the device is avoided. A concise summary of monopolar cautery and MRI safety is available. In general, monopolar cautery is safe in baclofen pumps and all shunt hardware. Monopolar can only be used in DBS and VNS devices if they are turned off preoperatively.

It is not uncommon for a pediatric surgeon or plastic surgeon to be asked to excise lumps or bumps on the skull of a young child. Most of these masses will be dermoid cysts. A general rule is not to surgically approach anything in the midline of the skull without intracranial imaging or neurosurgical input. Dermoid cysts can extend intracranially and even intradurally. They are nontender, firm, rubbery lesions to palpation that inevitably enlarge. Rupture and drainage through a sinus tract are possible in all locations ( Fig. 18.5 ). Often diagnosed in the infant, they also can manifest later in life. Midline lesions are associated with the higher likelihood of intracranial extension, particularly in the occipital region. Anterior fontanelle dermoids can be adherent to the dura of the sagittal sinus, and respect for this anatomy is paramount when resecting these lesions.

Dermoid cyst ( asterisk ) is shown overlying the anterior fontanel in an infant. Air ( arrowhead ) is seen within a draining dermal sinus tract.

Langerhans cell histiocytosis (LCH) is second in frequency to dermoid cysts. Solitary LCH is usually present after infancy, and the lesions are characteristically tender and mushy to palpation. They are associated with bony destruction. They can have a far-ranging natural history from spontaneous regression of a single skull lesion to being associated with infantile disseminated progressive multiorgan disease (Letterer-Siwe disease). For isolated skull lesions, curettage is often curative. Larger lesions can be associated with dural erosion and significant vascularity. Involvement of a pediatric oncologist is important with LCH to help exclude the more severe varieties of multisite disease and to guide adjuvant therapy.

Atretic encephaloceles can be found in the midline region of the vertex. They are often associated with differences in hair density and quality of the involved skin and tend to remain small. A skull defect, though often mechanically inconsequential, is always present. Associated intracranial venous anomalies also can exist. Bothersome lesions that are either tender or bulky can be excised. It is important to not mistake a dermoid with intracranial extension for an atretic encephalocele. An incompletely excised dermoid cyst will recur. All of these are electively treated conditions that are best handled by a pediatric neurosurgeon.

Defects in closure of the neural tube during development can be divided into two broad categories: myelomeningoceles and encephaloceles. Meningoceles differ from myelomeningoceles in that the spinal cord is not involved in a meningocele; these lesions are very rare ( Fig. 18.6 ). Myelomeningoceles, also commonly referred to as open spina bifida, can involve any level of the spinal cord, but the lumbar region is most common.

A lumbar meningocele ( diamond ) is seen with a surrounding cutaneous hemagioma ( arrowheads ).

Myelomeningoceles represent a failure of primary neurulation. Neurulation is the process of the two-dimensional embryonic nervous system rolling or folding into a three-dimensional tube or cylindrical structure. The neural tube usually completes closure at approximately day 28 of gestation. When the tube fails to completely close at a spinal level, the anatomic result can be a myelomeningocele ( Fig. 18.7 ). The causes of myelomeningoceles are poorly understood, but folic acid supplementation in the maternal diet prior to conception and during the first trimester reduces their incidence. Genetic and teratogenic influences likely play roles as well.

Newborn with a lumbar myelomeningocele before operative repair.

Except for cervical myelomeningoceles, the site of the defect dictates the level of neurologic function. With cervical myelomeningoceles, there remains spinal cord function caudal to the lesion. On the other hand, a baby with an upper lumbar myelomeningocele (at approximately L2) may be expected to have hip flexor function (iliopsoas, L1–2), but no knee extension (quadriceps, L3–4), absent motion at the ankle or toes (L5–S2), and impaired function of the bowel/bladder (S2–4).

The defect in the spine leads to more than just functional problems. The entire neural axis is affected both during and after development. The egress of CSF into the spinal defect allows mechanical changes to occur more rostrally, resulting in descent of the posterior fossa structures (both brain stem and cerebellum) into the cervical canal, which is known as the Chiari type II malformation. The anatomic abnormalities that lead to the Chiari II malformation occur almost exclusively in children with a myelomeningocele. (The Chiari I malformation will be discussed later.) Lower cranial nerve dysfunction can be life-threatening early in the life of these children and can occur due to maldevelopment of brain stem nuclei or compression of the medulla as hydrocephalus transmits further pressure into the Chiari II anomaly. Also, the supratentorial brain is not immune from injury, and hydrocephalus, polymicrogyria, enlarged thalamic adhesion (intermediate mass or middle commissure), beaked midbrain tectum, and interdigitated falx are often seen. Approximately one-third of these children have below-normal intelligence.

Neonatal myelomeningocele management is straightforward. The defect should be kept covered with a sterile, moist dressing. Prophylactic antibiotics are often administered following birth and continued through the postoperative period. Surgical closure is not an emergency but should be performed in the first 72 hours of life to reduce the incidence of infection. The treatment (timing and technique) of any hydrocephalus varies greatly by surgeon and institution. Relative indications for hydrocephalus treatment are progressive macrocephaly, an OFC growing greater than 1 cm per week, a bulging fontanel, split cranial sutures, downward gaze deviation, lower cranial nerve dysfunction, or CSF leak from the back closure site. Ventricular size by itself is not a good determinant of the need for a VPS in this population because infants with small ventricles may require VPS, and infants with large ventricles can sometimes be safely observed.

Prenatal closure has resulted in a significant reduction in the development of the Chiari II malformation and hydrocephalus. ^, However, approximately half of these infants still have hydrocephalus that requires treatment. Recent expansion of evidence supporting prenatal closure has also pointed to improved functional motor levels, improved bowel/bladder control, reversal of Chiari II on MRI, and significant improvement in brainstem dysfunction compared with postnatal closure. Advances in prenatal closure may involve the less invasive form of fetoscopic closure; however, larger cohorts are needed before solid conclusions can be drawn.

Caudal spinal cord dysfunction produces almost universal problems with bowel and bladder control, so urologic procedures are commonplace. When entering the abdominal cavity of a child with spina bifida, whether to deal with the peritoneal end of a VPS or treat a primary intraabdominal process, the surgeon should remember the possibility of preexisting conduits such as a Mitrofanoff stoma that may be hidden within the umbilicus.

Encephaloceles represent problems of neural tube closure at the more rostral end of the neuroaxis ( Fig. 18.8 ). Anterior encephaloceles are more common on the Asian and African continents. Posterior/occipital encephaloceles are more common in the Western world. Most encephaloceles are dramatically obvious on clinical examination; however, some anterior encephaloceles involving the skull base are difficult to see. Encephaloceles that herniate through the anterior skull base into the nasopharynx can manifest with obligate mouth breathing. There is often hypertelorism, though it may be subtle. The critical point is not to biopsy a nasopharyngeal mass without prior imaging. A simple transnasal biopsy of a skull base encephalocele can cause a CSF fistula into the nasopharynx followed by bacterial meningitis. Moreover, the more common posterior encephaloceles have a very high incidence of brain developmental problems and hydrocephalus. The child’s neurodevelopmental outcome tends to correlate with the amount of brain tissue in the encephalocele. The treating neurosurgeon also needs to be aware of critical vascular structures that may be present in the encephalocele sac before undertaking repair.

An occipital encephalocele ( asterisk ) is seen in this newborn. This encephalocele contained critical vascular structures from the deep venous system and was repaired in stages.

Skull shape abnormalities or perceived abnormalities in the neonate or infant are very common reasons for pediatric neurosurgical consultation. Only in the setting of multiple fused sutures and life-threatening increased ICP is there ever an urgency for treatment. However, early diagnosis is important because the treatment options diminish with age. Beyond a certain age, the quality of outcome diminishes, depending on the type of craniosynostosis.

The most common skull shape abnormality is acquired and can be labeled as “positional molding,” “positional plagiocephaly,” or “posterior plagiocephaly.” This acquired deformation is best understood by considering the neonatal skull as a parallelogram with all corners being hinges. Compression and flattening posteriorly on one side leads to advancement or protrusion of the ipsilateral anterior side of the cranial vault and base ( Fig. 18.9 ).

Drawing demonstrating the parallelogram effect and shifting of ear position.

From Youmans and Winn Neurological Surgery , 7th ed., Figure 196–1.

The above “acquired” abnormalities are best treated by nonsurgical means. True craniosynostosis differentiation and diagnosis are best done by a plastic surgeon or neurosurgeon with expertise in pediatric craniofacial abnormalities. Because some forms of craniosynostosis are best treated early in infancy, immediate referral to a specialist is important when craniosynostosis is suspected. Imaging studies are rarely needed for diagnosis but are more useful for operative planning and assessment of intracranial abnormalities driving skull shape, such as hydrocephalus, signs of raised ICP, and Chiari malformations.

Although somewhat of a simplification, a way to understand head shape abnormalities with craniosynostosis is based on principles put forth by Virchow. This principle is that bone growth occurs perpendicular to the normal cranial suture as the child’s head enlarges during the period of rapid brain growth in infancy. When a suture is fused, bone growth cannot occur efficiently perpendicular to the fused suture. Therefore, compensatory growth occurs perpendicular to the sutures remaining open. For example, when fused, the midline sagittal suture that separates the two parietal bones does not allow for normal biparietal widening. The open coronal and lambdoid sutures are sites of bone growth perpendicular to those respective sutures. The outcome is a head shape narrowed in the biparietal diameter but elongated in the anteroposterior dimension. This head shape is referred to as scaphocephaly caused by sagittal synostosis ( Fig. 18.10 ). This entity is best evaluated earlier in infancy so that all surgical options can be considered because the less invasive techniques are not as effective after 4 months of age.

Three-dimensional CT scan is from a neonate with sagittal synostosis. The arrows show the fused sagittal suture. The resultant ridge is often palpable and sometimes even visible on physical examination.

The other midline suture is the metopic suture that separates the two frontal bones. It runs from the anterior fontanel to the nasofrontal suture (between the eyebrows). This is normally the first suture to close. Ridging of the suture in infants is quite common because of this physiologic early closure. This ridging can be both palpable and visible. Simple ridging of the metopic suture can be considered a normal variant with no need for any workup or intervention. However, when the suture fuses too early (prenatally), the resulting deformity can lead to trigonocephaly. Trigonocephaly is a triangulated head when viewed from above ( Fig. 18.11 ). The forehead is pointed along with hypotelorism, and there is compensatory biparietal bossing. This type of craniosynostosis can cosmetically improve with time, unlike other forms of craniosynostosis . However, when it is severe, operative intervention is required to correct the deformity.

Preoperative and intraoperative photographs of the same patient with metopic craniosynostosis and severe trigonocephaly.

Either one or both coronal sutures can prematurely fuse. In the setting of unilateral coronal synostosis, the deformity creates significant asymmetry to the skull, orbits, and face. The fused coronal suture prevents advancement of the forehead on the involved side and elevates the sphenoid wing of the skull base. The forehead appears swept back and elevated. This leads to the ipsilateral eye appearing more open and higher because the orbital volume is shallower. In contrast, the contralateral side has compensatory frontal bossing making the contralateral eye look as though there is ptosis of the lid ( Fig. 18.12 ). It is not uncommon for these children to be referred to an ophthalmologist first before it is recognized that the true pathologic process lies with the skull.

(A and B) Three-dimensional CT depiction of left unilateral coronal synostosis. Note absent left coronal suture ( star ), the upswept left orbital rim ( arrowhead ) causing ocular misalignment, and the flattened left forehead ( black arrow ). There is compensatory right frontal bossing ( asterisk ).

Bilateral coronal synostosis, though a symmetric deformity, can lead to more critical problems. The orbital volumes may be so shallow as to not allow full eye closure when the child sleeps, which risks exposure injuries of the cornea. In addition, there can be growth restriction of the brain as the ability of the other sutures to compensate for more than one fused suture may not be present. This process can lead to an elevated ICP as the brain continues to grow but is not afforded enough room for growth. In syndromic cases such as Crouzon syndrome, in which the lambdoid sutures can be involved as well, there is a high incidence of Chiari I malformations (to be discussed later). Barring the more critical complications of multisuture craniosynostosis, operative correction is often delayed until after 6 months of age when the bone is thicker and allows for a more durable surgical reconstruction of the frontal bones and orbits.

Isolated lambdoidal synostosis is exceedingly rare. When suspected in a child, that child should be evaluated by a specialist in craniosynostosis. Unlike the parallelogram effect of positional molding, lambdoidal synostosis creates more of a trapezoidal head shape when viewed from above, as growth is restricted on the involved side, and contralateral compensatory parietal bulging develops. The ear on the involved side is commonly displaced slightly inferior and posterior relative to the contralateral ear. The degree of true cosmetic deformity with this type of synostosis is mild compared with the other forms, but it can at times require surgical intervention.

Salient points regarding head shape abnormalities in infants are (1) the diagnosis can almost always be made clinically without the need for imaging studies, (2) not all head shape abnormalities require therapy, and (3) early referral to a specialist is important to avoid unnecessary testing and ensure any necessary intervention is implemented at the appropriate age.