8 Congenital Hydrocephalus
8.1 Introduction
Congenital hydrocephalus is defined as the buildup of excessive amounts of cerebrospinal fluid (CSF), in the brain that presents at birth. In the United States, the prevalence of congenital hydrocephalus is believed to be ~ 5 cases per 10,000 births with a 2:1 male predominance.1,2,3
Congenital hydrocephalus can be divided into primary (idiopathic) hydrocephalus, which constitutes the majority of cases, or secondary (acquired) hydrocephalus. Stenosis of the aqueduct of Sylvius accounts for ~ 10 to 20% of congenital hydrocephalus. Intrauterine infections (e.g., cytomegalovirus, toxoplasmosis, rubella, and bacterial infections), spina bifida and other neural tube defects, posthemorrhagic hydrocephalus of prematurity, congenital brain tumors, and arachnoid cysts account for the other causes. Additionally, there are anatomical brain malformations frequently associated with congenital hydrocephalus, including Chiari malformation, Dandy–Walker syndrome, and Bickers-Adams syndrome (X-linked hydrocephalus).4
Several demographic and risk factors are associated with increased risk of congenital hydrocephalus. These include very low birth weight, lack of prenatal care, multiple gestation, maternal diabetes, maternal chronic hypertension, gestational hypertension, alcohol use during pregnancy, low socioeconomic status, being black and hispanic as compared with white, and male gender.2,5
8.2 Clinical Features
The signs and symptoms of congenital hydrocephalus vary depending on age (premature versus full-term infant), degree of hydrocephalus at birth, the primary etiology, and the time over which the hydrocephalus evolves. Clinical characteristics are summarized in Table 8.1 . Most of these signs and symptoms are due to an increase in intracranial pressure.
Premature infants | Full-term infants |
Apnea | Irritability |
Bradycardia | Vomiting |
Hypotonia | Sunsetting eyes |
Acidosis | Seizures |
Rapid head growth | Rapid head growth |
Tense fontanelle | Decreased feeding |
Splayed cranial sutures | Increased drowsiness |
Vomiting | Tense fontanelle |
Sunsetting | Distended scalp veins |
| Splayed cranial sutures |
| Poor head control |
Head circumference is an important feature that must be followed up using percentile curves. In a healthy premature infant, the head circumference generally increases ~ 1 cm per week. In premature infants with progressive hydrocephalus, the head circumference may increase more rapidly than the normal rate. On the other hand, full-term infants with hydrocephalus often have both macrocephaly and rapidly increasing head circumference. Normal head circumference for a full-term infant is 33 to 36 cm at birth, then increases by ~ 2 cm/mo during the first 3 months, by 1.5 cm/mo during months 4 and 5, and by ~ 0.5 cm/mo from months 6 to 12.
8.3 Diagnosis
Neuroimaging studies that visualize the ventricular system are useful for diagnosing congenital hydrocephalus. Prenatal fetal ultrasound is highly reliable and accurate in diagnosing hydrocephalus, as early as 16 to 22 weeks of gestation.6,7 This technique is safe, has no radiation hazard, is portable, and is less expensive than computed tomography (CT) or magnetic resonance imaging (MRI). Ventriculomegaly is assessed on ultrasound by measuring the diameter of the lateral ventricles at the level of the atria. The normal fetal lateral ventricular diameter is 10 mm. Ventriculomegaly is considered mild if the atrial diameter is between 10 and 15 mm and severe if > 15 mm.8 While ultrasound is generally preferred, CT is fast, reliable, and does not interfere with implanted metal devices. However, the radiation exposure hazard is a major drawback, with increasing evidence that this excessive exposure is associated with an increased risk of developing neoplasms.9
Although ultrasound can detect hydrocephalus very early, it may fail to reveal associated fetal anomalies, particularly those causing CSF obstruction. MRI studies are especially useful in detecting pathologies responsible for CSF pathway obstruction, such as tumors compressing the CSF flow, and provide a better evaluation of the posterior fossa. Additionally, MRI cine flow studies synchronized to the cardiac cycle can provide useful information to distinguish between communicating hydrocephalus and obstructive (non-communicating) hydrocephalus, to localize the level of obstruction in obstructive hydrocephalus, and for postoperative follow-up in patients with ventriculoperitoneal shunts and endoscopic third ventriculostomies.10 Therefore, MRI can be used as a confirmatory study to the earlier ultra-sound findings.11
Follow-up ultrasound examinations are important to look for regression or progression of ventriculomegaly. Approximately 90% of early isolated mild ventriculomegaly cases resolve, decrease, or remain stable by the third trimester.8,12 Moreover, follow-up ultrasounds have detected abnormalities missed on initial scans in 13% of cases.13
8.4 Treatment
The treatment of hydrocephalus includes both medical and surgical interventions. Most cases of congenital hydrocephalus are treated with simple ventriculoperitoneal (VP) shunting, and endoscopic procedures, such as endoscopic third ventriculostomy (ETV), are used in selected cases. Additionally, other neuroendoscopic techniques have been used in complex hydrocephalus, including choroid plexus ablation, septostomy, ventricle and cyst fenestration, and more recently, aqueductoplasty with or without stenting, lamina terminalis fenestration, and fenestration of the foramen of Magendie and foramina of Luschka.
8.4.1 Medical Management
Pharmacologic treatment aims to decrease CSF production and increase CSF absorption. Medications commonly used to decrease CSF production are diuretics, mainly, acetazolamide and furosemide. Acetazolamide is a carbonic anhydrase inhibitor and furosemide is a loop diuretics. These drugs have been widely used in the treatment of posthemorrhagic hydrocephalus. However, due to an association with a higher rate of shunt placement and increased morbidity and mortality, the evidence recommends against their use for posthemorrhagic hydrocephalus.14 Osmotic diuresis was previously another choice of medical therapy. However, although osmotic diuretics have been used to provide temporizing measures, they (e.g., mannitol) are no longer used in the treatment of hydrocephalus.15
8.4.2 Surgical Management
Cerebrospinal Fluid Shunting
CSF shunting is the most common treatment for diverting an excess accumulation of CSF. Shunting involves placing a mechanical system to prevent accumulation of excessive CSF by diverting it to the peritoneum or another extra-axial location such as the right atrium of the heart or the pleural space, allowing for its absorption and/or return into the systemic circulation, bypassing the site of obstruction.
A shunt consists of three main components: a proximal (ventricular) catheter placed into a CSF space such as a lateral ventricle, a one-way valve system, and a distal catheter that diverts the CSF to body cavities. There are many types of valves made by different manufacturers. The most commonly used system in practice today is a pressure-dependent valve, which opens when the pressure in the ventricle exceeds a certain value. Flow-controlled valves, on the other hand, allow a constant flow of CSF regardless of pressure gradients and patient position. Siphon-resisting valves are used to avoid siphoning of CSF and the consequent complications caused by of overdrainage. The choice of which valve to use is based on the neurosurgeon′s preference and experience. No conclusive data exists to recommend one particular valve over another and there is no difference in shunt failure rates among the various designs.16
A recent innovation in shunt technology has introduced programmable valves, which allow external adjustment of the opening pressure with the use of a special magnetic device. The main advantage of these programmable valves is to avoid additional operative procedures when the patient needs a valve with a different opening pressure, especially in cases of overdrainage, underdrainage, or in children who need to change opening pressure periodically. Nonetheless, studies show both programmable and conventional valves have similar safety and efficacy.17
Complications of Cerebrospinal Fluid Shunting
Shunt Infections
In spite of meticulous adherence to sterile techniques at the time of surgery, shunt infections are still seen after shunt placement. Shunt infection is a common complication, occurring in ~ 5 to 15% of procedures. More than 70% of shunt infections develop within 1 month of surgery and > 90% within 6 months.18 This complication is associated with significant morbidity and mortality. It may lead to ventriculitis, deterioration of cognitive function, and even death.19 Patients usually present with fevers, headaches, elevation of inflammatory markers, erythema along the shunt tract, and, if it is severe enough, to cause obstruction and signs and symptoms of increased intracranial pressure.
Shunt infection is most commonly caused by Staphylococcus epidermidis and Staphylococcus aureus.20,21 Treatment always commences with wide-spectrum antibiotic therapy. Additionally, in an attempt to further decrease shunt infection rates, antibiotic-impregnated catheters (AIS) have been introduced into practice. In a large retrospective study of 353 shunt placements, AIS catheters were independently associated with a 2.4-fold decrease in infection rates.22 Further, a well-performed meta-analysis established that prophylactic perioperative antibiotics and antibiotic-impregnated catheters do reduce the risk of shunt infection by ~ 50%.23
According to a recent study surveying all active members of the American Society of Pediatric Neurosurgeons (ASPN), most neurosurgeons remove the infected shunt system and place an external ventricular drain (EVD).24 The second most common method of treatment is externalizing of the shunt.
The duration of antibiotics treatment following shunt removal and EVD insertion is extremely variable ranging from less than a week to a few weeks.24 Kestle and colleagues conducted a recent multicenter pilot study of 70 patients from 10 institutions.25 Patients were followed up for 1 year following their CSF shunt infection. Interestingly, the incidence of reinfection was not related to the duration of antibiotic treatment.25
Mechanical Failure
Mechanical failure is another important cause of shunt malfunction. Approximately 40% of mechanical failure occurs within the first year after shunt insertion, and 5% more per year in subsequent years.16,26 Obstruction of the ventricular catheter is responsible for more than 50% of first shunt failures. This can be explained in part by the mechanism of overdrainage, which greatly reduces ventricular size. This causes the catheter to lie against the ependymal cell layer and choroid plexus, therefore blocking the holes at the end of the catheter. Approximately 15% of shunt failure cases are caused by fractured tubing. Catheter migration and dislodgement contribute to 7.5% of shunt failure cases.27 CSF mechanical failure requires urgent operative revision. When possible, a new catheter can be placed before removing the obstructed one.
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