and Spencer W. Beasley2
(1)
Department of Urology, Royal Children’s Hospital, Melbourne, Australia
(2)
Paediatric Surgery Department Otago, University Christchurch Hospital, Christchurch, New Zealand
Abstract
The embryology of the neural tube is described briefly followed by how to assess the neonate with spina bifida and the older child for spina bifida occulta.
Defects caused by failure of neural tube fusion may present as posterior midline swellings anywhere from the bridge of the nose to the tip of the coccyx. Many are associated with severe neurological deficit or related malformations of the central nervous system such as hydrocephalus. One of the most common neural tube abnormalities is anencephaly, in which the cephalic part of the neural tube has failed to close. The vault of the skull is absent, exposing the deficient cerebrum with only the brain stem and cerebellum remaining. The abnormality is not compatible with life, and fortunately, most fetuses with this abnormality are stillborn. Meningoceles and encephaloceles are discussed further in the chapter on cranial abnormalities (Chap. 10).
In this chapter, the various presentations of spina bifida are described so that an adequate initial assessment can be made at birth or whenever the abnormality is diagnosed. These anomalies require highly specialized neurosurgical, orthopaedic and urological management, but the primary physician needs some knowledge of the clinical problems so that initial management and referral can be performed correctly.
Embryology
The neural tube forms as a thickening of the dorsal ectoderm 2 weeks after conception, with complete fusion of the neural tube 8–10 days later. Hence, neural tube defects represent a very early and fundamental abnormality of embryogenesis. In the severe abnormality of myelomeningocele, the neural tube remains completely unfused and incompletely covered by skin, exposing the meninges to the outside. In the less severe meningocele, there is protrusion of the meninges through a defect in the spinous processes, but the swelling is completely covered by skin (Fig. 18.1).
Fig. 18.1
The aetiology of meningocele (10 %) and myelomeningocele (90 %); the different clinical states are produced by defects at different stages of neural tube fusion
In the least severe form of spina bifida, spina bifida occulta, there is a defect of the dorsal arches of the vertebrae but no protrusion of the meninges.
The cystic form of spina bifida, including myelomeningocele, is readily apparent at birth, while occult spina bifida may not present until adolescence. In the latter abnormality, a posterior defect in the spinal canal is associated sometimes with either a dermal sinus connecting with the subarachnoid space, a vascular malformation, lipoma, hairy patch or hairy naevus. These abnormalities represent dysplasia of the ectoderm overlying the neural tube defect.
Neonatal Assessment of Spina Bifida
When a new baby is seen with obvious cystic spina bifida, the clinician must assess:
1.
The neurological deficit, including motor and sensory loss and bladder and bowel function
2.
The presence or absence of hydrocephalus
3.
Orthopaedic deformities of the spine, hips and feet
4.
Other coexisting abnormalities
There may be some features in the obstetric history which have pointed to the abnormality, although once the child is born, the lesion is very obvious. Antenatal ultrasonography in the second trimester may have detected the abnormality, and there may be a record of high serum and amniotic fluid concentrations of α-fetoprotein. This protein escapes into the amniotic fluid and maternal circulation from the exposed surface of the myelomeningocele. When a meningocele is covered by normal skin, the α-fetoprotein concentrations remain normal. The prenatal diagnosis of myelomeningocele may be an indication for caesarean section.
Examination of the Lesion
The first step in the clinical examination is to determine the level of the neural tube defect in relation to the bony landmarks of the spinal column. The level of the lesion is important since the degree of neurological deficit depends on the segment of spinal cord involved. Lumbosacral lesions are the most frequent (Fig. 18.2).
Fig. 18.2
The frequency of spina bifida in relation to the level of the spine. Lumbosacral lesions are by far the commonest
After estimating its level, the lesion should be examined carefully to determine whether there is a complete covering of skin or whether the unfused neural tube is exposed. When a myelo-meningocele is not covered by skin, it is almost invariably associated with paralysis. Commonly, the unfused neural tube is present in the middle of the lesion (Fig. 18.3) and may leak cerebrospinal fluid or tissue fluid from the exposed neuroepithelium. Once physical abrasion and bacterial contamination stimulate the production of granulation tissue, the fluid weeping from the open lesion is more likely to be transudate from the granulations.
Fig. 18.3
The common lumbar type of myelomeningocele
If the spinal cord is not visible on the surface of the lesion, its position within the sac can be determined by transillumination (Fig. 18.4).
Fig. 18.4
Transillumination of a skin-covered sac will determine whether it contains the spinal cord
The adjacent skin commonly shows evidence of dysplasia with abnormal hair production, capillary vascular anomaly (‘port wine stain’) or a lipoma. After the myelomeningocele has been examined, the surface should be covered with a protective, non-stick dressing to reduce physical trauma and diminish the risk of infection.
The appearance of a meningocele is different, since the skin overlying the cystic lesion is likely to be intact. Meningoceles have a more even distribution along the vertebral column than myelomeningoceles, which are most commonly found in the lumbosacral region. A communication with the subarachnoid space can be determined by direct pressure on the skin-covered lesion which will cause the fontanelle to bulge. Conversely, during crying when the intracranial pressure is elevated, the lesion will become more tense (Fig. 18.5). The posture and spontaneous movement of the child usually indicates no serious neurological anomaly exists (Fig. 18.6).
Fig. 18.5
When the neck of the sac communicates with the cerebrospinal fluid, pressure on the sac will make the fontanelle bulge. Conversely, the sac is tense during crying
