Fetal And Neonatal Cerebral Ventriculomegaly Biology Essay

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Abstract. Ventriculomegaly is an increase in cerebral ventricular dimensions. It could be secondary to increased cerebrospinal fluid pressure in the ventricular cavity (hydrocephalus), or to a lack of brain parenchyma due to atrophic involution or arrested development. Ventriculomegaly causes diagnostic, therapeutic, and prognostic dilemma for obstetricians, neonatologists, and neurosurgeon. Mild fetal cerebral ventriculomegaly or borderline ventriculomegaly is defined as an axial diameter > 10 mm across the atrium of the posterior or anterior horn of lateral ventricles at any gestation. Moderate ventriculomegaly is atrial diameter larger than 15 mm; residual cortex larger than two mm in diameter and severe (atrial diameter larger than 15 mm residual cortex smaller than two mm in diameter). Sonographic demonstration of adducted thumbs in combination with ventriculomegaly and other intracranial abnormalities should prompt the diagnosis of X-linked hydrocephalus spectrum. Fetal brain magnetic resonance imaging, echocardiography, abdominal ultrasonography, karyotype, and serologic tests for congenital infections are indicated. Neonatal ventriculomegaly could be just due to increased width of cerebral ventricles or with increased cerebrospinal fluid volume i.e. hydrocephalus. Hydrocephalus could be obstructive (non-communicating) hydrocephalus or non-obstructive (communicating). Also, hydrocephalus course could be active (decompensated or progressive) or compensated (arrested). Intraventricular hemorrhage is the most common cause of acquired hydrocephalus (post-hemorrhagic hydrocephalus) in preterm neonates. Progressive hydrocephalus is associated with head circumference, crossing centile lines or expanding at over 1.5-2 mm/day, a tense anterior fontanel and separation of the cranial sutures, apnea, vomiting, and abnormal posture. Prevention and management of post-hemorrhagic hydrocephalus is very challenging. Shunt operation is the definitive treatment of progressive hydrocephalus due to any cause.

Key words: Aqueduct stenosis, CNS malformations, fetal, hydrocephalus, intraventricular hemorrhage, meningomyelocele, neonatal, perinatal, post-hemorrhagic hydrocephalus, post-hemorrhagic ventricular dilatation, ventriculomegaly

1. Introduction

The term "ventriculomegaly" (VM) is often used interchangeably with hydrocephalus (HCP). However, VM means enlargement of the ventricles, which may be caused by increased intraventricular pressure secondary to obstruction of cerebrospinal fluid (CSF) flow i.e. "HCP", or it may be the result of passive enlargement caused by atrophy of the brain parenchyma. VM could be detected antenatal by the obstetrician during routine maternal follow up (fetal VM) or diagnosed after delivery (neonatal VM) (1).

2. Fetal VM

Congenital lateral cerebral VM is among the most common brain abnormalities that can be detected by routine ultrasonography (US) (2). The incidence of congenital cerebral lateral VM ranges between 0.3 to 1.5 in 1000 births (3). Isolated VM accounts for 30-60% of fetuses with enlarged lateral cerebral ventricles (4).

In spite of the advances in US, the early diagnosis of fetal VM or HCP remains a diagnostic challenge. As, any cases of VM does not become apparent until 16th to 18th postmenstrual weeks or later. Also, in the second trimester the ratio of the lateral ventricles is higher compared to the brain parenchyma, but as the fetus approaches term this ratio decreases. At, 20th postmenstrual weeks of gestation the lateral ventricular shape is more "plump" but still within the normal limits for this age. While at term, the normal fetal lateral ventricle appears slit like. Therefore, fetal age must be assessed when looking for the presence of VM (5).

Quantitative and qualitative methods can be used to assess the fetal brain. The qualitative method depends on suggestive changes in the shape of the lateral ventricles and the appearance and the mobility of the choroid plexus (dangling choroid plexus sign). The quantitative method is done by measuring the ventricular size. The commonly used normal values for fetal lateral ventricles were generated using measurements obtained transabdominally (TA) in the axial plane.

The volume of the fetal brain can be obtained transvaginally, or TA by multi-planar imaging of the brain (three-dimensional US 3D). In addition, the volume can be saved and reviewed later (6).

2.1. Definition

Although mild or borderline VM is well defined and got an accepted norms among radiologists, there is no accepted definitions for grading moderate or severe VM. Most define them as moderate to severe VM (Fig. 1). Fetal cerebral VM is defined as an axial diameter > 10 mm across the atrium of the posterior or anterior horn of lateral ventricles at any gestation through TA scans. The atrial diameter is constant at 7.6 ± 0.6 mm (mean ± SD) from 14th to 38th weeks of gestation (7).

2.1.1. Mild or borderline VM

The widely accepted definition is an atrial width of 10-15 mm on the transverse plane. Isolated Mild VM is VM in the absence of other demonstrable central nervous system (CNS) anomalies (8). Other proposed definitions include an atrial width of 10-12 mm (9) and a distance greater than four mm between the medial wall of the ventricle and the glomus of the choroid plexus (10).

2.1.2. Moderate-to-severe or overt VM

There is no accepted consensus about either moderate or severe VM as separate grading. Most define a moderate to severe or overt VM as ventricles >15 mm wide (11-13).

2.1.3. Moderate

It is atrial diameter > 15 mm and residual cortex > two mm in diameter (14). Another definition by Levine et al. (15) is maximum width of the atrium of the lateral ventricle at least 15 mm but there is still more than three mm of cortical mantle.

2.1.4. Severe

It VM is atrial diameter > 15 mm and residual cortex < 2 mm in diameter (14). Another definition by Levine et al. (15) is maximum width of the atrium of the lateral ventricle at least 15 mm but there is no more than three mm of cortical mantle.

2.2. Etiology

VM can arise from agenesis of the corpus callosum, cerebral maldevelopment or destruction, cerebral vascular anomalies, or an obstruction within the ventricular system (16,17).

2.2.1. Inherited X-linked HCP spectrum (L1 Disease)

It comprises approximately 5% of all cases. These related neurological syndromes are caused by mutations in the gene at Xq28 encoding for the L1CAM (L1 neural cell adhesion molecule). Mutations in this gene are also responsible for other syndromes with clinical overlap that are frequently referred to as the X-linked HCP spectrum. There can be significant phenotypic variability within families, with some males being severely affected and diagnosed already during pregnancy, while others may have no macrocephaly and long survival (18). These related diseases are:

• Congenital stenosis of the aqueduct of Sylvius: Congenital HCP and resultant macrocephaly due to stenosis of the aqueduct of Sylvius may occur in isolation but is frequently associated with other features, including hypoplastic or flexed adducted thumbs.

• MASA Syndrome (Mental retardation, Aphasia, Shuffling gait, and Adducted thumbs).

• CRASH Syndrome (Corpus callosum agenesis/hypoplasia, Retardation, Adducted thumbs, Spastic paraplegia, and HCP).

• X-linked spastic paraplegia (SP 1) patients are mentally retarded and have spastic paraplegia.

• MR-CT syndrome (X-linked Mental Retardation-Clasped Thumb).

• Some forms of X-linked agenesis of the corpus callosum (19).

2.2.2. Acquired

Congenital infections caused by maternal prenatal infection as (toxoplasmosis, syphilis, cytomegalovirus, rubella) have been strongly associated with increased HCP prevalence. Teratogenic and neoplastic causes can lead to VM due to cerebral malformations or HCP (20,21).

2.3. Diagnosis

Fetal cranial US and magnetic resonance imaging (MRI) are important tools for the diagnosis and follow up of VM. They are also of great value for prognostication and obstetric management. Whether VM is isolated or associated with other malformation, non-progressive or progressive will affect the management and prognosis of VM (Figs 1-5).

Fetal cranial US is used to determine the degree of VM. The transverse diameter of the atria is used as a standard. Starting at around 13-15 weeks of gestation, the transverse diameter of the atria is stable in size and is usually less than 10 mm, with an average of about 7.6 mm. If the difference between the right and left sides is greater than two mm, VM is considered asymmetric.

Separation of the choroid plexus from the medial wall of the lateral ventricle is used to diagnose VM if > 3 or 4 mm, even when the ventricular measurement is borderline, and this can be a useful sign to follow over time (8-12).

Fetal brain MRI should be recommended because the prognosis of fetal VM is related to the presence of additional abnormalities. The prenatal detection of such abnormalities is critical. Although US is the principal technique for screening the fetal brain, it can be limited in detecting abnormalities of the brain parenchyma. Fetal MRI can detect additional sonographically occult CNS abnormalities in up to 40%-50% of cases of fetal VM (22). If VM is detected on ultrasound, the patient may undergo a fetal brain MRI to determine the severity of the finding and can detect associated brain malformation (23-25). Sonographically occult findings include developmental abnormalities, such as agenesis of the corpus callosum, cortical malformations, periventricular nodular heterotopia, cerebellar dysplasia, partial agenesis of the septum pellucidum, Walker-Warburg syndrome, and pontocerebellar dysplasia and destructive abnormalities, such as periventricular leukomalacia, porencephaly, multicystic encephalomalacia, intraventricular hemorrhage (IVH), and subependymal hemorrhage (26,27).

The diagnosis of X-linked HCP spectrum could be done by the presence of adducted thumbs in combination with VM and other intracranial abnormalities. A flowchart for management of fetal cerebral VM is constructed (Fig. 6).

2.4. Obstetric management

Multiplanar examination of the fetal brain with a high-resolution vaginal probe should be done for patients at risk for fetal cerebral VM (because of a previously affected child, or because of maternal infections). VM may develop only in late gestation or after birth, particularly with the X-linked HCP spectrum. The patients at risk for X-linked HCP spectrum should be informed that a normal mid trimester US does not rule out this condition (17).

Couples with a previously affected child should receive genetic counseling, because sometimes a generic diagnosis of congenital HCP may hinder a more complex anomaly with significant genetic implications. For example, patients at risk for X-linked HCP spectrum should be offered DNA analysis, as the recurrence rate is high and mid trimester US is frequently unsuccessful (28). Karyotyping should be done for fetuses with associated anomalies as they are at greater risk for an underlying chromosomal abnormality (29,30).

Termination of pregnancy could be an option for severe VM associated with other structural malformations such as spina bifida will usually carry a poor prognosis (31). Dandy-Walker malformation has an 80% risk of developmental delay in survivors by 4 years of age (32).

Fetuses with apparently isolated VM present a difficult group. Karyotyping will identify chromosomal anomalies in 3-4% of cases, most often trisomy 21 (33).

If termination of the pregnancy is considered, information should be collected quickly so that the parents can reach a decision. Rapid karyotyping for amniocentesis using quantitative fluorescent polymerase chain reaction will give a result within 48 hours (34). Even if termination of pregnancy is arranged, the prenatal karyotype offers the best chance of making the diagnosis of trisomy. Karyotyping after termination has a risk of failure of cell culture (35).

In the absence of a chromosomal abnormality or any structural malformation there remains the possibility of both death and handicap. Termination of pregnancy with stable fetal VM, where the risk of handicap is between 9% and 36%, is a difficult and complex issue (36,37).

2.5. Fetal surgery

The treatment of VM in-utero can be very challenging. It is an option for treating fetuses with isolated progressive VM to improve brain development. Fetal MRI should be performed before in-utero surgery. VM due to aqueductal stenosis (HCP) is traditionally detected and then treated after birth with a shunt procedure.

Ventriculo-amniotic shunt (the placement of a tube between the fetal ventricular system and the amniotic cavity to reduce pressure) - the results of fetal surgery for isolated progressive VM are not encouraging. Theoretically decompressing the ventricles may prevent adverse effects on the developing brain, although in-utero treatment with ventriculoamniotic shunts has not led to improved perinatal outcomes (38).

Surgical repair to fetuses with meningomyelocele in-utero has been proposed as a way to improve neurological outcomes. Although reduction in hindbrain herniation and reduction in shunt-dependent HCP has been reported, long-term effects on brain function have not been determined (39-45).

Cephalocentesis can be done prior to delivery to reduce the cranial size and allow for vaginal delivery. Cephalocentesis is indeed associated with a perinatal mortality in excess of 90 percent. It can be reserved for babies with questionable viability to allow vaginal delivery (46,47).

2.6. Planning delivery

A trial of labor is indicated in most infants with VM and vertex presentation, as most of them do not have macrocrania. The pediatric team should be informed well in advance of delivery, and a definitive plan should be available for the obstetric and neonatal team. Delivery is better to be delayed until fetal lung maturity is documented, avoiding cephalocentesis unless non-viable baby, and using cesarean section for obstetrical indications only are general recommendations. Elective cesarean section is indicated if there is cephalo-pelvic disproportion (46).

2.7. Recurrence risk

Congenital VM is mostly multifactorial except for X-linked HCP (recurrence risk 50% of males). Families with a previously affected child have a recurrence risk of 4%. VM associated with abnormal findings and structural malformations, even when isolated, will often carry a poor prognosis from disability to death. Infants with a prenatal diagnosis of mild VM have abnormal neurodevelopment in 10% to 36% dependent on associated anomalies, etiology, and ventricular measurement (29,48). Unilateral mild VM carries a favorable prognosis when isolated (49,50).

3. Neonatal VM

3.1. Definitions

VM in the neonatal period could be either due to HCP or decreased parenchymal volume and malformations. HCP has many definitions and types. It could be classified according to the timing into congenital or acquired, and to level of CSF circulation abnormality into obstructive or non-obstructive. Also, it could be classified according to the disease course into progressive (active or decompensated HCP) and stationary course (arrested or compensated HCP).

Obstructive or non-communicating HCP occurs when CSF flow is blocked within the ventricular system. Non-obstructive or communicating HCP occurs when the CSF leaving the fourth ventricle is restricted in its flow over the surface of the brain, or if the sites of absorption are not functioning adequately (51).

Obstructive or non-obstructive HCP can be a congenital or an acquired condition (52). Congenital HCP means that the condition existed before birth. While, acquired HCP develops after birth, for a variety of reasons, such as trauma, post hemorrhagic, scar tissue formation, or CNS infection (53,54).

Arrested HCP or (compensated HCP) is that the size of the ventricle remained the same from one ultrasound to the next. Criteria for diagnosing arrested or compensated HCP are near normal ventricular size, normal head growth curve and normal psychomotor development (55). Progressive HCP is the ventricle increases in size from one ultrasound to the next manifested with symptoms and signs of increased intracranial tension and progressive head expansion. An arrested HCP may become active or progressive and a progressive HCP may arrest or compensate (56).

True HCP must be distinguished from transient VM, which is common following IVH but resolves completely within four weeks, and static VM, which occurs secondarily to the loss of cerebral tissue either because of the destruction, or the failure of development, of cerebral white matter following IVH (57).

3.2. Etiology

Congenital HCP has an estimated incidence of about three to four per 1000 live births (58). Chiari malformations and aqueductal stenosis are the most common causes of congenital HCP due to structural defects. Dandy Walker malformation is a less frequent cause of congenital HCP. Other causes associated with congenital HCP are intrauterine infections, especially toxoplasmosis, rubella, cytomegalovirus, and syphilis (59,60).

In the neonatal period, acquired causes of HCP include perinatal infections and intracranial bleeding secondary to trauma or anoxia. Premature infants are particularly susceptible to IVH, which may subsequently lead to HCP. Arterio-venous malformations of the great vein of Galen or the straight sinus may also present in this period and may cause HCP secondary to blockage or rupture. Rare causes of HCP in the neonatal period include arachnoid cysts, congenital choroid plexus papillomas, and tumors (61).

3.3. Mechanism of ventriculomegaly

Causes and mechanisms of neonatal VM and HCP are summarized in Table 1.

3.3.1. Congenital

Chiari malformation is a set of congenital anomalies of the hindbrain where there is a downward herniation of the brainstem and cerebellum through the foramen magnum. Three types were described depending on the degree of herniation. Chiari type I is herniation of the cerebellar vermis or tonsils through the foramen. In type II, the fourth ventricle and lower medulla are also herniated. The Chiari type III is herniation of the cerebellum through the foramen magnum and an associated cervical spina bifida. Chiari type II is the most common type and almost always associated with a myelomeningocele and HCP (62).

Congenital aquaductal stenosis occurs in 0.5 to 1.0 per 1000 live births, accounts for approximately 20% of HCP cases. Although commonly recognized antenatal or at birth, the disorder may have an insidious onset, and should be considered in the differential diagnosis of HCP at any age. Aqueductal stenosis results from narrowing of the aqueduct of Sylvius and leads to obstructive, non-communicating HCP. One form of aqueductal stenosis, associated with the syndrome of X-linked HCP, is caused by a mutation of the X-linked recessive L1 gene, which is responsible for the production of specific neuronal cell adhesion molecules (61).

The Dandy-Walker malformation is a cystic dilatation of the fourth ventricle. It is due to partial or complete agenesis of the cerebellar vermis, which leads to obstruction of CSF outflow through the foramina of the fourth ventricle. It occurs in approximately 1 per 30,000 live births, and is associated with less than five percent of all cases of HCP (58,61). Although the defect is present at birth, HCP will be diagnosed by one year of age in approximately 80% of all Dandy-Walker malformations. The diagnosis of HCP may be delayed until adolescence or adulthood in some cases (61).

3.3.2. Acquired HCP

Acquired aqueductal stenosis due to gliosis, can result from destruction of ependymal cells after a hemorrhagic or infectious process (toxoplasmosis, cytomegalovirus and mumps encephalitis) (59).

IVH is becoming an increasingly important cause of HCP secondary to the increased survival of extremely preterm infants. Post-hemorrhagic ventricular dilation has high morbidity and mortality (63). IVH is the result of vascular instability of cerebral vessels in the germinal matrix at the level of the head of the caudate nucleus in the premature infant. Bleeding of these vessels has been classified into four grades. Grade I is hemorrhage only within the germinal matrix. Grade II hemorrhage extends from the matrix into the ventricles, but without ventricular dilatation. Grade III is IVH with resultant ventricular dilatation. Grade IV is IVH with ventricular dilatation and spread of bleeding into the surrounding brain parenchyma. IVH usually occurs in low birth weight infants within 72 hours of delivery (64).

Post hemorrhagic HCP (PHH) is defined as progressive VM caused by disturbances in CSF flow or absorption following IVH. PHH may occur immediately as a result of multiple blood clots obstructing the ventricular system or channels of CSF reabsorption initially. Permanent HCP is induced by the inward migration of fibroblasts and collagen deposition in the CSF pathways (65). The breakdown products of blood lead to chronic obliterative arachnoiditis of the basal cisterns and deposition of extracellular matrix proteins in the foramina of the fourth ventricle and the subarachnoid space (66). Diffuse fibrosis of the leptomeninges leads to communicating HCP within weeks to months after IVH. Intraventricular blood and ventricular expansion adversely affects the immature periventricular white matter by a variety of mechanisms, including physical distortion, raised intracranial pressure (ICP), free radical generation, and inflammation. Obstruction to CSF circulation causes obstructive HCP (67,68).

3.4. Diagnosis

3.4.1. Neuroradiologic studies

Cranial US remains the main stay as bedside diagnosis of IVH in preterm neonates. All preterm neonates born at less than 30 weeks' gestation should receive screening cranial US at age 7 to 14 days and again at 36 to 40 weeks postmenstrual age. Detection of IVHs significantly alters clinical care, and diagnosis of periventricular leukoencephalopathy or low-pressure VM alters the prognosis and outcome. A non-contrast computed tomography (CT) should be done to any encephalopathic term infant with birth trauma, low hematocrit or coagulopathy to detect hemorrhage, which is a major cause of cerebral palsy in term infants. MRI should be performed when the infant is between 2 and 8 days of age to look for evidence of hypoxic-ischemic injury, if the CT is negative for hemorrhage (69).

3.5. Management

Management of neonatal VM depends on the etiology, associated malformations, and whether it is an increase in ventricular width without increase in CSF volume or it is HCP. If the diagnosis is HCP, it should be assessed whether it is compensated or active HCP (Figs 7 and 8).

Once the underlying etiology has been diagnosed, the main therapy for progressive HCP is a shunt procedure, which allows for diversion of CSF and ventricular decompression. Medications that reduce ICP such as mannitol may be used for cases of rapidly progressive HCP while awaiting surgery. Also acetazolamide and furosemide can be used (70).

Treatment of PHH is more difficult than other types of HCP, due to the presence of large amount of blood and protein level in the CSF together with the small size and instability of the preemies makes an early VP shunt operation contraindicated. Shunt complications are more common if done early (71).

Infants with a clinical picture of active HCP and significant VM require treatment early in life. This includes bulging fontanel, deteriorating neurological status, increased irritability, absent cerebral diastolic velocity (not explained by a patent ductus arteriosus) or excessive head expansion of 2 mm/day (e.g. 1.4 cm over 7 days), some consider expansion of head by 1.5 mm/day as excessive (72,73).

Infants with mild or moderate VM and head circumference within the reference range may not require initial treatment. In these infants follow up for the first few months of life, and monitoring of the head circumference and repeat US, CT, MRI are helpful to decide whether shunting is needed or not (69). Normal head growth at this age is approximately 1 mm per day (74).

CSF drainage by repeated lumbar or ventricular tapping, and/or the use of acetazolamide and furosemide to reduce CSF production can be done awaiting VP-shunt for rapidly progressive HCP (75,76).

Acetazolamide (100 mg/kg/per day) reduces CSF production by 50%. The combination of acetazolamide and furosamide reduces CSF production by 100%. Neonates on acetazolamide should have serial renal US because of the possibility of nephrocalcinosis. The potential toxic effects of acetazolamide on myelination should be considered before the initiation of treatment. A clinical trial demonstrated the use of these drugs to be ineffective (77).

3.5.1. Lumbar and ventricular taps

Lumbar puncture (LP) (for communicating HCP) or trans-fontanel ventricular tap (for non-communicating or failed LP to reduce ventricular size or ICP) is carried out with the objective of removing 10-15 mL/kg over 10-20 min (78). If the LP fails to drain enough to normalize head growth to <2 mm/day, a ventricular reservoir is indicated. Failure of LP may be associated with obstruction of CSF pathways by blood clots and the change of type from communicating HCP to obstructive type (75-79).

3.5.2. Subcutaneous reservoir

Intermittent taping through a subcutaneous reservoir is a frequently used option. The major complications of subcutaneous reservoir are skin necrosis, shunt infection, ventriculitis, subdural hygroma and liquor fistula (80).

3.5.3. External ventricular drainage

External ventricular drainage can be performed through a shunt inserted into the dilated anterior horn of the right lateral ventricle. The proximal end of the catheter is tunneled subcutaneously and is connected to the drainage system which can continuously remove CSF by 10-15 mL/kg for 5-7 days. The amount of CSF removed can be adjusted by elevating or lowering the drainage system (78,81).

3.5.4. Surgical therapy of HCP

Ventricular shunt is an artificial device; made mostly of plastic (some parts may be metal). It includes a catheter inserted in the ventricle of the brain, a one-way valve that allows the unidirectional flow of CSF out of the brain, and a distal catheter that drains the CSF to an extracranial location in the body. The most preferred distal site remains the peritoneum. Other sites for insertion for rare difficult cases with coexisting abdominal problems can be used, such as the right atrium, the gall bladder, the ureter, or the bladder. In current practice VP shunt is most commonly used (82).

Essentially two types of shunts exist: Pressure-regulating shunt is designed to maintain a difference of pressure between their inlet and outlet, and they allow flow of CSF once that preset pressure has been reached. The differential pressure valves are more prone to cause over drainage complications. While, flow regulating shunts allow a constant flow of CSF, simulating the normal flow of CSF. The flow regulating valves are more prone to valve obstruction (83,84).

Shunt insertion for PHH could not be done until sterile CSF with no cells and protein <1.5 g/L is obtained and the infant has acceptable weight. (This weight is usually 2.5 kg but could be lower in individual cases). If there is intra-abdominal pathology such as necrotizing enterocolitis, which contraindicates a VP shunt, tapping the reservoir continues until the abdomen normalizes. Very rarely, another type of surgical shunt may have to be considered. Usually, a low-pressure valve system is used in shunting babies with PHH (76,78-81).

In children with open myelomeningocele, simultaneous shunting and closure of myelomeningocele should be performed, if feasible. It appears to protect patients from CSF leak from the spinal wound, which can lead to shunt infection, and it improves the chances for better development by reducing intracranial hypertension early (85,86). If closure of the defect has been delayed, CSF infection may have already taken place. In such circumstances, CSF testing for infection should be performed, and if present, external ventricular drainage should be employed for 7-10 days together with antibiotic treatment, till control of CSF infection and a shunt can be inserted (87-89).

Spina bifida requires follow-up for life to detect and treat problems associated with it. Urologic problems because of neuropathic bladder usually require intensive medical and surgical treatment (90). Orthopedic problems, such as scoliosis and foot deformities, also require careful follow-up because they are likely to require surgical treatment (91). Shunt complications

Shunt malfunction is a fairly common occurrence with a one-year failure rate of 30-40% (92). Higher rates of failure have been described in younger patient populations with the most significant risk occurring in patients younger than six months of age at the time of implantation. The most common time for shunt failure to occur is within 6 months of surgery. Causes of shunt malfunction are obstruction, infection, and over-drainage (92,93).

Infections usually presents about two months after shunt insertion. Infection rates vary from 1-10%. The most common causative agent is coagulase-negative staphylococci, especially Staphylococcus epidermidis. Staphylococcus aureus has also been implicated. Treatment usually necessitates removal of the shunt. Intraventricular and intravenous antibiotics may be required. If shunt revision is necessary, sterility of the CSF should be confirmed first by culture prior to surgery (92-94).

Endoscopic third ventriculostomy has a success rate of 70% when used in aqueduct stenosis, and it is the procedure of choice in this subgroup of patients. It can be done for patients with HCP associated with myelomeningocele. Follow up MRI scanning with phase-contrast sequence is mandatory to verify patency of the stoma (95-97).

3.6. Outcome

The overall outcome and prognosis of VM is highly dependent on various factors including the age of onset, etiology, ventricular expansion, and extent of neurologic damage prior to correction of the intracranial insult (Figs 9 and 10).

Mortality rates have been reduced to less than 5% in ten years after shunt placement (98). Shunts have improved the outcome of patients with HCP dramatically. In the absence of any complex developmental syndrome, and with careful treatment and follow-up, patients with HCP are expected to survive and reach adulthood. Simple aqueduct stenosis is associated with very good outcome. At least 50-70% of these patients can attain an intelligence quotient higher than 80, which is considered normal (99).

Children with spina bifida are expected to have normal intellectual abilities, with the main problems caused by the physical disabilities related to the level of spinal cord damage. Children with myelomeningocele without HCP have normal intelligence. Posthemorrhagic or postmeningitic HCP is associated with poor outcome. This is because of the underlying brain parenchyma damage (100).