Neural tube defects, large heads and hydrocephalus

17.4 Neural tube defects, large heads and hydrocephalus



Peter Flett, Ray Russo



Neural tube defects


The neural tube is the embryological structure from which the brain and spinal cord develop. The term neural tube defect (NTD) refers to a group of malformations involving the brain and/or spinal cord in association with varying degrees of absence or malformation of the overlying tissues: meninges, bone, muscle and skin. Anencephaly occurs when the neural tube fails to close at the head, and the brain and skull bones do not develop normally. Myelomeningocele (myelo meaning ‘cord’; meninges, coverings of the spinal cord; cele, ‘sac’) involves all the tissue layers including the skin and bone, and is an outpouching of the spinal cord through the posterior bony vertebral column that has failed to form. Meningocele is an outpouching of the meninges or coverings of the spinal cord only, and not the cord itself. The term spina bifida refers to the normal bony projection over the spine being divided or ‘bifid’. Spina bifida occulta is the failure of the formation of the posterior elements of the vertebrae but without any outpouching of the meninges or spinal cord. It occurs in 5–10% of the population and is most often asymptomatic. X-rays of the spine documenting the incomplete vertebral arch confirm the diagnosis. Accompanying associated features may include dermal hyperpigmentation, a fatty swelling, a tuft of hair or a dermal sinus on the back. Spina bifida cystica refers to myelomeningocele and meningocele. Myelomeningocele is the more serious and commoner type of spina bifida cystica. Spinal dysraphism, which includes spina bifida occulta, meningocele and myelomeningocele, is part of the family of NTDs that encompasses abnormalities of the cranium and its contents (anencephaly, encephalocele and cranial meningocele) as well as abnormalities of the spine.



Incidence


The incidence has varied in different countries, the highest rates being recorded in the past in Northern Ireland, the west of Scotland and south Wales. In South Australia, the total incidence of NTDs during 1966–1991 was 2.01 per 1000 births and the incidence of myelomeningocele was 0.97 per 1000 births, with no upward or downward trend. Despite the total incidence remaining stable, prenatal diagnosis and termination of pregnancy resulted in an 84% fall in the birth prevalence of all NTDs during the years studied. Screening by serum α-fetoprotein (AFP) measurements or mid-trimester ultrasonography, or both, detected more than four-fifths of cases in 1986–1991 in South Australia.


Recurrence risks in families such as close relatives have been documented extensively. Recurrence risk statistics suggest a polygenic or environmental aetiology. The risk of recurrence following the birth of the first child with a NTD is approximately 4–8%, or 1 in 25. A woman is at equal risk of either spina bifida or anencephaly in future pregnancies, regardless of whichever of these NTDs occurred in the previous pregnancy. The risk increases to at least 10% after the birth of two affected children.


NTDs are found commonly in spontaneous first-trimester miscarriages. They are also more common in females than in males, in lower socioeconomic groups, different ethnic groups, and in women taking certain anticonvulsant drugs.



Embryology and pathogenesis


The human neural tube closes just before the 30th day following fertilization and thus any influence affecting the closure of the neural tube must be present before this early stage of pregnancy. The typical motor, sensory and sphincter dysfunctions of spina bifida and myelodysplasia are the most evident clinical manifestations but represent only one aspect of this complex teratological anomaly. There is a high incidence of gross and microscopic brainstem, cerebellar and cerebral malformation. The aetiology of NTDs is still debated. Polygenic inheritance and environmental and teratogenic factors have been implicated. It has been demonstrated unequivocally that vitamin supplementation with folic acid reduces the incidence of recurrence in high-risk populations. Dietary factors may therefore play a major part in low-risk populations. Many other potential aetiological causes have been examined also during the last 20 years.



Antenatal diagnosis, antenatal counselling and fetal surgery


The presence of abnormally high levels of AFP in the amniotic fluid has a high correlation with myelomeningocele. AFP is a component of fetal cerebrospinal fluid (CSF) and it probably leaks into the amniotic fluid from the open NTD. Closed lesions often do not cause increased AFP levels. The false-positive rate for the determination of myelomeningocele is less than 0.5% and the false-negative rate is 2%. AFP is synthesized by the yolk sac, hepatic cells and gastrointestinal tract of the fetus and is normally excreted in the amniotic fluid in fetal urine. The detection rate for open NTDs using maternal serum screening is approximately 80%, with a low false-positive rate. Ultrasonography can detect or confirm the extent of the NTD.


Offering counselling for the family with an antenatal diagnosis of a NTD is important, especially as the family will probably consider their options about whether to continue with the pregnancy or elect for termination. Great care should be taken about the information conveyed. Preferably, it should be given by a specialist experienced in caring for children with a NTD, in an appropriate environment and with time available to answer the family’s questions about all the facets of raising a child with this diagnosis. The antenatal scan can offer some guidance, but it must be remembered that ultrasound scan findings cannot predict all aspects of functioning (physical and cognitive) accurately. In addition, families can be offered further counselling through community-based organizations (e.g. the Spina Bifida and Hydrocephalus Association). All families should be made aware of preventative measures (periconceptional folate) and offered genetic counselling if they wish to have other children in the future.


Fetal surgery (for closure of the myelomeningocele lesion) at 20–30 weeks’ gestation, after which the fetus is returned to the uterus, has been developed with the hope of preventing significant complications in the affected child. Early studies have demonstrated good cosmetic closure of the lesion but the complication rate (primarily due to the fetus being delivered prematurely) was found to be high. The primary outcome is a significant reduction of the development of hydrocephalus in the treatment group.



Clinical features


NTDs may be classified as in Box 17.4.1.



Box 17.4.1 Classification of neural tube defects



Anencephaly




• At birth, presents as an opened, malformed skull and brain


• Most babies are stillborn


• No effective treatment is possible


• Death usually occurs within hours or days



Cranium bifidum



Cranial meningocele




• The underlying brain is normal


• A meningeal sac protrudes through a skull defect



Encephalocele




• A midline sac protrudes that may contain brain


• Hydrocephalus is common



Spina bifida occulta (Fig.17.4.1)




• One or more vertebral arches are incomplete posteriorly but the overlying skin is intact


• Diagnosed incidentally, for example as the result of X-ray of the spine


• Spinal cord usually normal; however, abnormalities of the spinal cord can occur


• Ectodermal abnormalities may be associated with pigmented naevus, angioma, hirsute patch, dimple or dermal sinus on overlying skin


• The ectodermal component may communicate with the dura; may pose some risk of intraspinal infection (if associated with a dural sinus)


• The fatty swelling may be a lipomeningocele



Spina bifida cystica




• Meningocele (Fig. 17.4.2), where the spinal cord is not involved:


• Herniation consists of meningeal cyst filled with cerebrospinal fluid, in absence of other malformations, neurological signs are normal


• Not associated with hydrocephalus


• Constitute less than 10% of all cases of spina bifida cystica


• Myelomeningocele (Figs 17.4.3 & 17.4.4), in which vertebral column skin, meninges and spinal cord are involved:


• Almost always obvious at birth


• May occur anywhere along the length of the spinal column, with lumbar and lumbosacral regions being the most frequent anatomical levels


• Abnormal spinal cord tissue and nerve roots may be readily apparent macroscopically


• There may be spinal abnormalities such as kyphosis at the site of the lesion


• Functional deficits almost always include:


• Arnold–Chiari type 2 malformation and hydrocephalus

• paraplegia, with motor and sensory impairment; intellectual impairment and neuropathic sphincter disturbance (bowel and bladder)


Sacral agenesis




• Genetic disorder, marked by total absence of coccyx and lower two or three sacral vertebrae


• Functional deficits include flaccid neurogenic bladder, motor and, to lesser extent, sensory deficits of lower extremities


image

Fig. 17.4.1 Schematic representation of spina bifida occulta. (A) Dermal sinus. (B) Intraspinal cyst pressing on the cord. (C) Lipomatous mass infiltrating the cord elements.


image

Fig. 17.4.2 Meningocele: diagrammatic representation.


image

Fig. 17.4.3 A lumbosacral myelomeningocele.


image

Fig. 17.4.4 Myelomeningocele: diagrammatic representation.



Management of myelomeningocele


A team approach that includes the parents is essential for the proper management of myelomeningocele. An important factor, which compounds the disability, is that the defect is apparent at birth. Information given to the parents and the manner in which it is conveyed will influence their reaction at this most vulnerable time and will affect the future of the child and the family. Medical specialists in this team include the neurosurgeon, orthopaedic surgeon and urologist. The medical team leader is most appropriately a paediatrician or paediatric rehabilitation specialist with special skills in the field of child development and rehabilitation. The medical team leader will coordinate care but, importantly, will also manage and advise on the multiple problems experienced by the children and their families. These include disability issues, school integration, interventions to improve functional outcome, and various activities to support the parents and child through the many problems, both physical and psychological, that invariably arise. The physiotherapist, occupational therapist, speech pathologist, dietitian, orthotist, psychologist and medical social worker, together with trained hospital and community-based nursing staff and teachers, are important members of this team. The team has three major goals:



• to promote good health in the short and long term


• to promote maximum function in the child so that, as nearly as possible, normal developmental sequences and timing can be followed to enable maximal independence for the child and family


• to support good family functioning to assist the child to reach their maximum potential within the family and community.



Specific problems in the management of the newborn with spina bifida


It is possible to predict with considerable accuracy the potential for future impairment in a number of areas. These include ambulation and subsequent mobility, probable bowel and bladder function, and hydrocephalus, with its probable sequelae. It is much more difficult to predict the effects that these impairments will have on the lifestyle of the individual and family. Also, it is possible to recognize early those lesions that are inoperable because of massive bony deformity and extensive skin loss, which would prevent closure of the defect. The specific problems are as follows:



1. Children with high lesions (thoracic and thoracolumbar), significant hydrocephalus at birth, major kyphosis or other significant problems (either congenital or acquired) have a significantly increased mortality rate in early life and substantial morbidity if they survive. In these circumstances, in discussion with the family, supportive care only may be recommended. If the infant survives the perinatal period, elective surgical care may be indicated. In the absence of such adverse factors, in discussion with the family, early surgical repair/removal of the lesion usually is recommended.


2. Careful serial evaluation of head circumference and ventricular size by ultrasonography or computed tomography (CT) will indicate whether hydrocephalus is developing. Once it is established that progressive hydrocephalus is present, a shunt procedure is recommended.


3. Baseline orthopaedic, urological and neurosurgical assessments provide the basis for ongoing discussions with the family and management of the condition. Occasionally, active urological intervention is required for urinary retention.


4. It is critical to begin to establish an empathetic, therapeutic relationship with the parents in the newborn period that forms the foundation for ongoing support throughout childhood.



Ongoing management



Management of physical disability and mobility


Physiotherapists play an essential role in reducing deformities and encouraging mobility. Foot deformities are common at birth as a result of unopposed muscular activity in utero. Splinting and passive stretching are the mainstays of treatment in early life. Persistent foot deformities may require corrective orthopaedic surgery. Surgery also may be needed for dislocated hips, particularly if the child is likely to walk. At times, three-dimensional gait analysis (3DGA) is beneficial for surgical decision-making and can assist in planning for this intervention.


The outlook for walking depends on the level of the spinal cord lesion, intelligence and motivation. Most children with a lesion at L4 or lower will walk, with or without splints and crutches. Children with higher lesions may walk with orthotics in early childhood, but most will choose wheelchair mobility by mid to late childhood.



Spinal deformities


A significant proportion of children will develop scoliosis and many of these will require spinal instrumentation. Spinal jackets are not well tolerated and have a very limited role in the management of paralytic scoliosis.



Neuropathic fracture


Fractures of the lower limbs, due to osteopenia, are common in children with myelomeningocele. Fractures may occur with minimal trauma. Encouraging children to walk, or stand in a standing frame on a regular basis may improve the mineralization of long bones and lessen the likelihood of further fractures. However, nutrition, calcium and vitamin D from sunlight may also be important factors in management.



Sensory deficit and skin care


Pressure ulcers or burns in anaesthetic areas are common. Parents are encouraged to check anaesthetic areas daily for the presence of pressure sores. Early recognition and treatment is essential to prevent long periods of morbidity and hospitalization.



Neuropathic bladder


Almost all children with myelomeningocele have a neuropathic bladder. Failure to empty the bladder may lead to recurrent urinary tract infections, vesicoureteric reflux, renal calculi and hydronephrosis. Hypertension and renal failure may be seen in a small number of cases. Management of the neuropathic bladder is by clean intermittent catheterization performed four or five times daily by the parents, and later by the child. This is usually commenced at around 3–4 years of age, or earlier if repeated urinary infections occur. Prophylactic antibiotics may be required for recurrent urinary infections. Bladder augmentation and/or artificial sphincter operations may be indicated if the clinical situation dictates. The use of anticholinergic medications and of oxybutynin to increase bladder capacity may be tried. Regular assessment of renal function is essential throughout the person’s life.



Neuropathic bowel


Most children have limited or absent rectal sensation, and have little or no bowel control. Constipation with megacolon, faecal impaction and overflow incontinence is the major risk in spina bifida. Faecal softeners may be needed in infancy. Some children can attain continence simply by regular toileting, whereas others may need high-fibre diets, faecal softeners, suppositories or microenemas. Aperients are avoided whenever possible. Refractory cases may require regular bowel washouts. Another technique that may increase independence is the anterograde colonic enema (ACE). This surgical procedure creates a stoma on the anterior abdominal wall through which a catheter can be passed to allow for easier access for the provision of an enema. The advantage is that the enema is completed independent of others and can assist greatly in the management of refractory neuropathic bowel.

Related posts:

  1. Sudden unexpected death in infancy
  2. Birth defects, prenatal diagnosis and teratogens
  3. Resuscitation
  4. The newborn infant: stabilization and examination

Stay updated, free articles. Join our Telegram channel
Tags:
Aug 4, 2016 | Posted by in PEDIATRICS | Comments Off on Neural tube defects, large heads and hydrocephalus

Full access? Get Clinical Tree
Get Clinical Tree app for offline access