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Spinal Dysraphism[1]


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Spinal Dysraphism[1]

  1. 1. 111 2 3 4 27 5 6 Spinal Dysraphism 7 8 Simon Stapleton 9 1011 1 2 3 4 5 6 7 8 9 to convey. Spinal dysraphism includes both 2011 Summary conditions obvious at birth or before, such as 1 myelomeningocele (spina bifida aperta), and 2 Spina bifida represents a spectrum of condi- conditions of the spine which may or may not 3 tions of disordered development of the spine be apparent on closer inspection. This latter 4 and spinal cord. In its most severe form – group includes so-called occult dysraphism 5 open myelomeningocele – the neurological (spina bifida occulta), when the only hint of an 6 deficits can be profound, with implications underlying spinal abnormality may be a cuta- 7 for repeated and lifelong management, neous lesion or the development of orthopedic 8 although, with the concerted effort of a mul- or urological symptoms. 9 tidisciplinary team, the outlook for quality of Substantial progress has been made in the 3011 life may be good. The incidence of this con- understanding and management of these 1 dition is declining and may be reduced fur- conditions in recent years. Effective treatment 2 ther with the introduction of periconceptual of hydrocephalus and the multidisciplinary 3 folic acid supplements. approach to the needs of children with myelo- 4 Less obvious forms of spina bifida occur meningocele have led to improvement in the 5 and may not be immediately apparent at outlook for those affected. The realization of the 6 birth – occult spinal dysraphism – although importance of tethering as a mechanism for 7 there may be cutaneous manifestations of the deterioration in dysraphic states has meant 8 underlying condition. The concept of “tether- an improvement in the management of these 9 ing” of the spinal cord by a dysraphic condi- conditions, directed at the underlying neuro- 4011 tion has proved useful in the understanding logical problem, rather than the acceptance of 1 of the generation of symptoms and in the inevitable deterioration. A fall in the incidence 2 rationale for treatment of these disorders. of dysraphic lesions, improvements in diet and 3 the use of preconception folic acid, as well as a 4 better understanding of the genesis of these 5 Introduction conditions, will hopefully mean that fewer 6 children are affected in the future. 7 The term “spinal dysraphism” covers a range of 8 developmental conditions of the spinal cord and 9 its surrounding structures. Often also referred Epidemiology 5011 to as either spina bifida or neural tube defects, 1 spinal dysraphism is sufficiently all-encompass- Estimates of the true incidence of neural tube 2 ing to allow for the scope and complexity of defects occurring in pregnancy are difficult to 311 these conditions, which the other two terms fail ascertain, since a proportion of severely affected 475
  2. 2. 476 NEUROSURGERY fetuses are undoubtedly aborted spontaneously, prior to conception. In order to prevent a first 1111 early in pregnancy. Nevertheless, worldwide, occurrence of a neural tube defect, all women 2 the prevalence of neural tube defects occurring should be advised to take 400 mg of folic acid 3 at birth appears to be falling. This can be partly daily prior to conception, as well as increasing 4 attributed to screening programmes and possi- their dietary intake of foods rich in folic acid, 5 bly to improvements in nutrition, but the rate continued until the 12th week of pregnancy 6 also seems to be declining for unexplained (food high in folate includes green vegetables, 7 reasons. In the UK, the prevalence throughout yeast, beef extract and breakfast cereals fortified 8 the country is falling from an overall level of with folic acid) [2]. 9 approximately 4 per 1,000 live births in the 1011 1970s to in the region of 0.3 per 1,000 live births 1 now. There remains a significant geographical Etiology 2 variation in the prevalence of cases in this 3 country, with the highest rates occurring in the There is clearly a familial tendency to the devel- 4 west of the country, namely in western Scotland, opment of neural tube defects, although this is 5 Wales and Northern Ireland, where the inci- probably a polygenic mechanism. Siblings of an 6 dence may be more than twice as high as else- affected individual have an approximately ten 7 where, but the incidence in these areas is also times greater chance of also being affected 8 falling. Elsewhere in the world, the prevalence (2.5% vs approximately 0.2% risk in the general 9 rates are generally lower, ranging down to about population – see above). The children of healthy 2011 1 in 10,000 in sub-Saharan Africa. siblings of an affected child are known also to 1 There is a significant genetic component to be at increased risk. 2 the development of neural tube defects, since, if Nutritional factors are thought to play a 3 either parent has had an affected child or role and may explain partly the social class 4 if either parent is affected by the condition, differences in incidence. The use of preconcep- 5 there is an approximately 10% risk of further tion folic acid stems from the concept that 6 offspring having a neural tube defect. If low maternal folate intake is implicated in the 7 two affected pregnancies occur, the risk to a etiology of neural tube defects (see above). 8 further pregnancy is increased about 20-fold. Numerous teratogens have been identified in 9 Secondary prevention of further affected preg- animal models, including anticonvulsants such 3011 nancies requires screening techniques, includ- as valproate and phenytoin, other folate antag- 1 ing alphafetoprotein sampling and ultrasound, onists such as aminopterin, hypervitaminosis 2 with selective termination of affected pregnan- A, alcohol and mitomycin C. The extent to 3 cies. Primary prevention, however, requires the which these factors operate in humans remains 4 prevention of neural tube defects occurring in uncertain. 5 the embryo in the first place, even in pregnan- Recently, abnormalities in homeobox genes 6 cies not at higher risk of such an occurrence. have been implicated in the genesis of neural 7 Since the 1960s, it has been recognized that tube defects in mice. In particular, the human 8 women with an affected pregnancy had signifi- analogue of the mouse Pax3 gene has been iden- 9 cantly lower red cell folate levels than those with tified. It is unknown, however, whether this is a 4011 unaffected pregnancies. The Medical Research sine qua non in humans [3]. 1 Council Vitamin Study of 1991 [1], in which 2 women who had had a previous pregnancy 3 affected with a neural tube defect were ran- Embryology 4 domized to receive folic acid (4 mg daily) or 5 placebo, with or without other multivitamin Under normal circumstances, development of 6 supplements, demonstrated that the rate of the neural tube proceeds as follows. The sup- 7 affected subsequent pregnancy was significantly posed relevant deviations from this related to 8 reduced in the folic acid group (relative risk specific forms of dysraphism are described in 9 0.29). It is now, therefore, recommended that in the appropriate section. 5011 order to prevent a recurrence of a neural tube The primitive streak develops at the caudal 1 defect in subsequent pregnancies, 5 mg daily of end of the bilayered embryonic disc by devel- 2 folic acid should be supplemented to the diet opmental day 14. From the primitive streak, 311 476
  3. 3. 477 SPINAL DYSRAPHISM 111 cells migrate between the layers of ectoderm dural sheath. The process of secondary neuru- 2 and endoderm to form the embryonic meso- lation (vacuolation, condensation and fusion of 3 derm. Hensen’s node is located at the cranial the caudal cell mass) occurs after the overlying 4 end of the primitive streak and, from here, the ectoderm has fused to form the skin. 5 notochordal process develops in a cranial direc- 6 tion between the two embryonic layers by day 7 17. The solid notochord becomes a hollow cylin- Myelomeningocele 8 drical structure, which transiently fuses with the 9 underlying layer of endoderm. There exists, This is the single most common form of spinal 1011 therefore, a communication between the amni- dysraphism and is synonymous with spina 1 otic cavity dorsally and the yolk sac ventrally via bifida aperta or an open neural tube defect. 2 the primitive pit, known as the neurenteric It is the most severe form of spinal dysraphism 3 canal. This communication closes as the noto- and presumably represents a failure of closure 4 chord again separates from the endoderm by of the neural tube at approximately day 21 of 5 day 20. At this time, Hensen’s node and the development (primary neurulation). 6 primitive streak regress with growth of the 7 embryonic disc, in a caudal direction, ultimately 8 to lie in the low sacral or coccygeal region. Clinical Presentation and 9 The notochord induces the overlying ecto- Assessment 2011 derm to thicken and cells heap up to form the 1 neural plate. The neural groove develops in the Unless detected antenatally by ultrasound or 2 neural plate, producing lateral folds which ulti- maternal screening, open myelomeningocele is 3 mately meet in the midline as the neural groove immediately apparent at birth (Fig. 27.1). This 4 deepens, to form the neural tube. This is the manifests usually as a defect on the back, with 5 process of primary neurulation. Closure of the evidence of a neural placode representing 6 neural tube begins in the mid-thoracic region the open spinal cord, often with normal- and 7 and extends both cranially and caudally. At the 8 cranial end of the neural tube (the future lamina 9 terminalis), closure of the anterior neuropore 3011 occurs by day 24, while closure of the caudal or 1 posterior neuropore occurs by day 28. The loca- 2 tion of the posterior neuropore is a matter of 3 some debate but probably lies in the region of 4 L1 or L2. Caudal to this level, development 5 of the spinal cord does not occur by primary 6 neurulation. In this region, Hensen’s node and 7 the primitive streak give rise to an undifferenti- 8 ated clump of cells known as the caudal cell 9 mass, destined to form the conus medullaris 4011 and the filum terminale. This occurs by a rather 1 poorly defined process – secondary neurulation 2 – of vacuolation, condensation and subsequent 3 fusion to the spinal cord formed by primary 4 neurulation. The significance of this process in 5 the human remains rather uncertain. 6 As the process of primary neurulation occurs, 7 the ectoderm lateral to the developing neural 8 plate fuses in the midline to cover the neural 9 tube, while embryonic mesoderm from the scle- 5011 rotome at each level of the embryo migrates 1 towards the midline to surround the notochord 2 and the neural tube to give rise ultimately to the Fig. 27.1. Myelomeningocele in the lumbar region of a neonate. 311 vertebral bodies and neural arches, as well as the Note the cystic appearances, with fragile blood vessels visible. 477
  4. 4. 478 NEUROSURGERY abnormal-appearing nerve roots coursing from they been treated initially. McLone [5–7] has 1111 it ventrally and surrounded by arachnoid adhe- presented evidence that, with a concerted mul- 2 sions, an incomplete dura and associated para- tidisciplinary team approach whereby all open 3 vertebral soft tissues. The central canal of the myelomeningoceles are closed at birth, the 4 spinal cord may be visible at the rostral end of overall outcome with respect to mortality, intel- 5 the placode; the defect may be covered by a thin lect and mobility is not improved by selective 6 epithelial or arachnoid layer, but this may have non-treatment. 7 ruptured and CSF will be seen to leak from the Surgery for open myelomeningocele is aimed 8 defect. at protecting the existing neural structures and 9 There may be associated developmental preventing infection. Surgery will not restore 1011 anomalies, usually of the nervous system. Most neurological function; nevertheless, it is essen- 1 infants will develop hydrocephalus and a Chiari tial to preserve any functioning nervous tissue 2 II malformation is very common. Abnormalities that does exist. Because of the risk of infection, 3 of cerebral gyration, of the posterior fossa con- closure of the defect should be carried out 4 tents and agenesis of the corpus callosum, as within 48 hours of birth. Closure of the defect 5 well as associated vertebral anomalies, may also involves defining the neural placode and freeing 6 occur. Unsuspected, more rostral “occult” this from arachnoid adhesions. Some surgeons 7 forms of dysraphism may coexist. reconstitute the neural tube by folding over 8 Delivery of an infant with a suspected open and suturing the neural placode in an attempt 9 myelomeningocele should be by Cesarean to prevent future cord tethering; however, this 2011 section, in order to avoid the risk of infection procedure is not essential and may unnecessar- 1 during passage along the birth canal; the child ily damage the delicate existing nervous tissue 2 should be nursed on its front or side, with a if the sutures are inappropriately placed. 3 sterile moist dressing covering the defect, and It should be ensured that there are no skin 4 kept warm. Having examined the defect itself, appendages attached to the placode. The 5 clinical assessment aims at determining the extradural space is identified, the dura is mobi- 6 neurological deficit, both sensory and motor. lized and this plane developed around the 7 Much of this can be done by observation and defect to allow closure of the dura in a water- 8 gentle stimulation of the limbs to ascertain sen- tight fashion. If necessary, a dural graft may be 9 sation and movement. Bladder and bowel func- required to close the dura, without compromis- 3011 tion are difficult to assess with any certainty but ing the neural structures and maintaining the 1 a good urine stream may suggest an incomplete closure free from tension The muscle and fascia 2 deficit, although almost all children will go on either side of the defect are mobilized; this 3 on to have some degree of bladder and bowel may require lateral releasing incisions if the 4 disturbance. Further examination is directed defect is large, and then approximated. The skin 5 towards possible associated congenital ano- is then closed in a watertight manner. For very 6 malies and hydrocephalus, as well as general large defects, plastic surgical procedures with 7 cardiopulmonary status. myofascial or cutaneous flaps may be required 8 Without closure of the myelomeningocele, to achieve adequate closure. At all stages of 9 meningitis is likely to develop within a few days, the closure, it is essential that the tissue layers 4011 often with fatal consequences. In view of the are not approximated under tension, otherwise 1 severe, often devastating neurological deficits wound breakdown and CSF leakage will occur. 2 and the poor outlook for a fulfilling, self-caring Approximately 80% of children with myelo- 3 and dignified existence, Lorber [4] proposed a meningocele will require a shunt at some stage. 4 policy of selective non-treatment, based on the For those with obviously severe hydrocephalus, 5 level of the lesion, the severity of associated this may need to be carried out within several 6 hydrocephalus and degree of spinal deformity, days of closure of the spinal defect. For those 7 as well as the presence of other congenital children less severely affected, observation, with 8 abnormalities. This policy has clearly led to head circumference measurements and assess- 9 many severely affected infants not surviving. ment of signs of raised intracranial pressure, will 5011 Nevertheless, not all untreated infants suc- dictate the need for and the timing of shunt 1 cumb, with the effect that they may go on to insertion. The majority of children who will need 2 survive, with more severe disabilities than had a shunt will do so by the age of 5 months [8]. 311 478
  5. 5. 479 SPINAL DYSRAPHISM 111 Long-term Care and Outcome Again, bladder and bowel continence 2 depends chiefly upon the level of the neuro- 3 in Open Myelomeningocele logical lesion. Most children manage the 4 The long-term care and follow-up of children bladder with clean intermittent catheterization 5 with myelomeningocele requires the input of and many are able to perform this for them- 6 many disciplines, preferably in a combined selves. Management of the bowel depends upon 7 multidisciplinary clinic devoted to the manage- a combination of bulk laxatives and enemas, 8 ment of children with spina bifida and its avoidance of constipation and the use of a 9 complications. This will include assessment of Shandling catheter [11]. 1011 all aspects of physical, as well as cognitive, The long-term care and assessment of child- 1 development. ren with myelomeningocele requires attention 2 Overall survival with myelomeningocele after to many details of their development, with par- 3 the first 4 years appears to stabilize at approxi- ticular scrutiny for the possible complications 4 mately 85% [6], although there continues to be which may arise in time. From a neurological 5 a significant mortality. This can be related to perspective, aside from the ever present risk of 6 many of the associated problems faced by these shunt malfunction and Chiari malformation 7 children, including hind-brain disturbance, and syringomyelia-induced problems, this will 8 causing respiratory distress, apneic spells and include the possibility of cord re-tethering. 9 gastro–esophageal reflux with tracheal aspira- Re-tethering of the spinal cord (see below) 2011 tion, shunt malfunction and infection, and following closure of a myelomeningocele or 1 bladder and renal problems. after any other “untethering” operation, such as 2 Myelomeningocele itself does not appear after surgery for lipomeningocele, should be 3 to have a significant impact on intelligence. considered in any child with a clinical deterio- 4 Although the average IQ of affected children is ration. Re-tethering may manifest as a deterio- 5 below the mean, the majority fall within the ration in motor power or gait, pain, altered 6 normal range, with only 9% having an IQ score sensation or deformity in the legs, or with 7 below 70 in McLone’s series, followed up for changes in bladder function. Increasing scolio- 8 over 15 years. Factors which do seem to affect sis has also been considered to result from 9 intelligence include initially severe hydro- re-tethering. 3011 cephalus, neonatal ventriculitis and shunt Most neural placodes or lipomas probably 1 infections, as well as the level of the lesion. adhere to the dura soon after the initial opera- 2 Hydrocephalus and Chiari malformations pre- tion; however, it is only with continued trac- 3 sumably also account for the consistently found tion on the cord that symptoms are likely. Re- 4 deficits in fine motor function in the upper tethering remains a clinical diagnosis, since 5 limbs and in visuo–spatial processing, as well as static MRI will only show the location of the 6 changes in age-related language ability. Two- conus, rather than its mobility. 7 thirds of children, with appropriate support, Re-operation to release the cord should be 8 can be kept in mainstream education. Ultimate considered in any child with a significant clini- 9 employment opportunity seems to be related cal deterioration. There are often dense adhe- 4011 more to intellectual ability than to physical sions and thick scar, making surgery difficult, 1 disability [9]. and consideration to expanding the dura with a 2 Numerous factors contribute to mobility. The patch should be given. The results of surgery are 3 ability to walk will depend not only upon the reported to be gratifying in that most children 4 level of motor and proprioceptive deficit, but can be stabilized and pain is often improved 5 also on factors such as spasticity, deformity, [12]. 6 ataxia and obesity, as well as intelligence, 7 support and motivation. In McLone’s series, 8 75% of surviving children by school age were 9 mobile without a wheelchair; nevertheless “Occult” Spinal Dysraphism 5011 this figure declines with age [10], largely due 1 to increasing difficulty and effort required to The term “occult dysraphism” implies that 2 maintain posture, especially with weight the presence of the dysraphic condition is 311 increasing proportionately faster than strength. not immediately apparent, as it is in “open” 479
  6. 6. 480 NEUROSURGERY myelomeningocele. This may or may not be so venting the normal ascent of the spinal cord and 1111 at birth, but most dysraphic conditions of the conus relative to the bony spine during postna- 2 spine become apparent in one way or another tal growth and development. Coupled with the 3 in childhood or adolescence. The diagnosis repeated stretching of an already “taut” cord 4 may be suspected at birth by the presence of during everyday activity, this leads to neuro- 5 a lumbosacral lipoma or cutaneous lesion logical dysfunction and the development of the 6 with abnormal pigmentation in the midline. associated orthopedic and urological features. 7 Commonly, infants are referred with a sacral 8 dimple with a question as to the presence of a Spinal Cord Tethering 9 dysraphic condition. Shallow dimples, tethered 1011 inferiorly, in the natal cleft are generally inno- Central to an understanding of the development 1 cent. Any midline dimple above the natal cleft of symptoms in occult dysraphism is the 2 should be treated with suspicion, particularly if concept of spinal cord tethering. This is a 3 there is any history of discharge. Cutaneous dynamic problem with the spinal cord and 4 lesions often have abnormal pigmentation and cannot therefore be identified per se on static 5 may have an associated hairy patch. imaging such as MR or CT. Nevertheless, that 6 Other manifestations of “occult” dysraphism tethering may exist can be inferred by the pres- 7 include orthopedic problems such as scoliosis, ence of an abnormality such as a lipoma, bony 8 pes cavus or inequality of calf girth or foot size. spur or thickened filum terminale, producing an 9 Neurological abnormalities such as leg weak- abnormally long spinal cord with a low-lying 2011 ness or numbness are common presentations, conus. The implication is that the cord has been 1 usually with variable loss of lower-limb reflexes. held in its original position and prevented from 2 In older children, adolescents and adults, sen- ascending within its thecal sac during growth of 3 sory abnormality in the feet may lead to trophic the individual. There are a number of possible 4 changes, with smooth, shiny skin and occasion- explanations of why this should lead to neuro- 5 ally with ulcers which are slow to heal. The child logical dysfunction: 6 may be referred as being generally clumsy on his sustained traction on the cord with growth 7 or her feet. Disturbances of bladder or bowel of the bony spine leads to stretching of 8 function are also seen frequently. Constipation the cord itself and disruption of neuronal 9 requiring regular laxatives and delay in toilet function; 3011 training may be apparent after the age of 5 years, ischemia of the cord leads to abnormalities 1 when the child may still not be dry by day as well of oxidative metabolism [13]; 2 as by night. There may be evidence of a poor uri- 3 nary stream and frequent urinary tract infec- repeated hyperflexion (e.g. during sporting 4 tions. Pain as a feature of spinal dysraphism is activities) of the spine causes acute injury 5 uncommon in children but is a frequent occur- to neuronal processes at the level of the 6 tethering lesion. rence in adults either with a known dysraphism 7 or who may present for the first time in adult- Attempts have been made to “visualize” teth- 8 hood (see below). ering clinically using MR CSF pulsatility studies 9 Occult dysraphism may be suspected at birth [14] or to demonstrate motion of the conus 4011 by the presence of a visible abnormality but fre- using CT myelography in both prone and supine 1 quently presents during subsequent periods of positions, but the diagnosis remains a clinical 2 rapid spinal growth, at approximately age 6 one, based on the presence of a presumed teth- 3 years and in adolescence. Occasionally, presen- ering lesion and evidence of neurological dys- 4 tation may occur acutely at times of excessive function. 5 spinal motion, such as in sporting activities, If tethering is the underlying cause of neuro- 6 after being placed in the lithotomy position, logical deterioration in many dysraphic condi- 7 after childbirth and as an unsuspected underly- tions, the principle of surgical treatment is to 8 ing condition following surgical correction of untether the spinal cord and to prevent it re- 9 scoliosis. Such modes of presentation support tethering. This is generally achieved by remov- 5011 the idea that symptoms and signs in dysraphic ing the tissue responsible for the tethering or 1 conditions are the result of “tethering” of the detaching the spinal cord from it, as described 2 spinal cord by the underlying abnormality, pre- in the specific sections below. 311 480
  7. 7. 481 SPINAL DYSRAPHISM 111 Tight Filum Terminale in adulthood. Similarly, acute neurological dete- 2 rioration has been described. 3 The simplest and perhaps the most easily The approach to treatment of lipomeningo- 4 imagined form of spinal cord tethering is that cele depends largely upon the perceived natural 5 produced by a thickened, fatty, filum terminale. history of the condition. Arguments in favor 6 This may present with asymmetric neuro- of prophylactic untethering include the fact 7 logical or orthopedic abnormalities in the that many infants appear to be neurologically 8 lower limbs and is well seen on sagittal and axial normal, whereas most adolescents and adults 9 T1-weighted MRI as high signal within the present with some neurological deficits. In one 1011 filum associated with a low-lying conus. study [15], all children were symptomatic by the 1 Treatment simply involves division of the filum, age of 4 years. The condition therefore appears 2 ensuring that no nerve roots are attached to it. to carry a high risk of progressive deterioration, 3 On occasion, at operation, the proximal end of while the risks of surgery remain relatively 4 the filum may spring out of view superiorly, low. Once neurological deficits or orthopedic 5 providing convincing evidence of the tethering deformity have occurred, they tend not to 6 process. be reversible, even with surgery, and there is a 7 background risk of acute deterioration and 8 Lipomeningocele paraplegia without surgery. For these reasons, 9 many neurosurgeons consider untethering the 2011 Lipomeningocele is an abnormality of the spine cord before the age of 6 months or do so as soon 1 characterized by a low-lying conus medullaris, as the lesion is recognized thereafter [16,17]. 2 infiltrated with fatty tissue, which extends Counter to this argument is the fact that not all 3 through a bony dysraphic defect and into the children with lipomeningoceles do deteriorate 4 subcutaneous tissues. It is thought to occur as a as demonstrated by the occasional unsuspected 5 result of an abnormality of secondary neurula- adult presentation; that surgery does carry some 6 tion of the caudal cell mass, whereby pluripo- risk of neurological damage; and that acute 7 tential mesenchymal cells fail to regress and may paraplegia in the absence of any preceding 8 lead to lipomas, hamartomas and teratomas symptoms is rare. Added to this is the frequent 9 in the lumbosacral region. The lipoma is invari- problem of re-tethering after surgery. There has 3011 ably covered by skin but may have pigmenta- therefore been a reappraisal of the need for early 1 tion, hair or cutaneous dimples on it. They often prophylactic untethering and consideration of 2 lie asymmetrically across the midline in the lum- surgery only at the onset of the development 3 bosacral region and can reach a very large size. of symptoms. This requires close and regular 4 Intradurally, the lipoma may be attached to the assessment of all patients with lipomeningoce- 5 dorsal surface of the cord or it may be inserted les, to detect any neurological change [18,19]. 6 into the terminal end of the conus. The lipoma There is little argument over the place of surgery 7 may enlarge in infancy or may be associated with in preventing further deterioration in those pre- 8 obesity. Although uncommon, lipomeningoce- senting with progressive neurological deficits. 9 les may be associated with other developmental Recently, Chumas [20] has summarized these 4011 anomalies, including syringomyelia, Chiari mal- arguments and emphasized the need for long- 1 formation and anal and genitourinary malfor- term follow-up of all these patients if a consen- 2 mations. The lesion is considered to lead to sus is to be achieved. 3 tethering of the spinal cord, thereby producing Pre-operative assessment requires careful 4 symptoms. neurological examination of the legs and uro- 5 The cutaneous abnormality is frequently dynamic assessment. MRI in the sagittal plane 6 obvious at birth but, in the past, has not always clearly demonstrates the lesion (Fig. 27.2a) and 7 been recognized for what it is. Progressive, often will also show an associated hydromyelia. Axial 8 asymmetrical neurological deterioration in the images reveal the relationship of the lipoma to 9 legs is a common mode of presentation, as well the cord itself (Fig. 27.2b). 5011 as discrepancies in foot size and leg length in Surgery is aimed at untethering the spinal 1 older children. Bladder and bowel dysfunctions cord, reducing the bulk of the lipoma and recon- 2 are also frequent complaints. As with other stituting the dura to enable the conus to lie 311 forms of dysraphism, pain tends to be a feature freely. This may require a dural patch to try to 481
  8. 8. 482 NEUROSURGERY 1111 2 3 4 5 6 7 8 9 1011 1 2 3 4 5 6 7 8 9 2011 1 2 a b 3 4 Fig. 27.2. a Lumbar lipomeningocele. Sagittal T1-weighted MR scan, demonstrating a low-lying conus associated with a 5 lipomeningocele. The spinal cord ends in a lipoma, which itself is continuous with the subcutaneous tissues and is coupled with a 6 defect in the lumbar laminae. b Lumbar lipomeningocele. Axial T1-weighted MR image, revealing the relationship between the conus 7 and the lipoma itself. 8 9 prevent re-tethering by local scar tissue. Surgery conus, following even successful surgery, 3011 is generally carried out through a midline inci- may not change position on MRI studies, re- 1 sion, although plastic surgical considerations tethering can be difficult to prove radiologically 2 may need to be taken into account in large and re-exploration may be necessary on clinical 3 lesions. The first normal lamina above the lesion grounds alone (see above). 4 is identified and the dura here exposed. The Surgery carries a low risk for neurological 5 dura is then opened to expose the attachment of deterioration (less than 5%) and appears to 6 the lipoma to the cord and the opening contin- prevent the subsequent development of neuro- 7 ued around the exiting fatty defect. The line of logical deficits. In those with clinical signs of 8 fusion of the lipoma with the cord can then be tethering, surgery appears to be effective at 9 identified and, with the exiting nerve roots ante- preventing further deterioration and, for early 4011 rior to this line, the lipoma can be detached. The intervention, may reverse some of the neuro- 1 bulk of the lipoma can then be removed and logical dysfunction. For long established deficits 2 the dura closed, ensuring that the mobility with orthopedic deformity, surgery will not lead 3 of the conus is not compromised by the closure. to improvement but can effectively prevent a 4 The frequent difficulty in obtaining a satisfac- worsening deficit. 5 tory dural closure leads to the two chief com- 6 plications of the procedure: CSF leakage and Split Cord Malformations 7 re-tethering. The former is generally manage- 8 able with CSF drainage and re-suturing, if “Split cord malformation” is a term used to 9 need be. The latter may become apparent describe a number of congenital abnormalities 5011 within months or many years of the initial of the development of the spinal cord and 1 surgery and is characterized by the onset of its coverings, characterized by a division of 2 neurological deterioration or pain. Since the the cord into two, not always equal, parts. The 311 482
  9. 9. 483 SPINAL DYSRAPHISM 111 general term “split cord malformation” is hemicords to the dural sleeve. This Pang terms 2 preferable to the potentially confusing terms the “split cord malformation type II”. The 3 used to describe the conditions often referred to implication here is that both types of split cord 4 as diastematomyelia and diplomyelia. The malformation represent tethering lesions and 5 abnormality may take the form either of a divi- therefore both require surgical exploration 6 sion of the spinal cord within a single dural sac in order to prevent subsequent neurological 7 (diplomyelia, type II split cord malformation) deterioration. 8 or of splitting of two hemicords, each with its Split cord malformations are characteristi- 9 own dural covering, by a septum, usually made cally associated with a midline hairy patch or 1011 up of a bony spur and/or fibrocartilagenous “horse’s tail”. This is much more commonly 1 band (type I split cord malformation). found in split cord malformations than with 2 The embryological origin of split cord mal- other forms of “occult” dysraphism (Fig. 27.3). 3 formations remains unclear. The presence of There may occasionally be an associated dermal 4 two hemicords within a single dural tube has sinus or pigmented skin lesion. The spur is gen- 5 been considered to occur as a result of a dou- erally found in the lumbar or lower thoracic 6 bling of the neural tube without fibrous tissue region. Clinically, this may produce one leg with 7 dividing the cords and therefore without the muscle wasting or sensory loss, with or without 8 potential for causing tethering. On the other orthopedic manifestations, such as pes cavus. 9 hand, two hemicords, each with its own dural One or both ankle jerks are often absent. There 2011 sheath and surrounding bony structures, have may be involvement of the bladder and bowels, 1 been thought to be due to splitting of the noto- particularly in those children presenting in early 2 chord by an interposed adhesion between the adolescence. Scoliosis may also occur, as may 3 primitive endodermal and ectodermal layers or other vertebral anomalies. The anatomy of the 4 of incomplete persistence of an accessory defect is demonstrated on MRI scans; particu- 5 cranial neurenteric canal. This leads to a septum larly well seen on axial imaging are the two 6 splitting the cord and, with growth, tethering as hemicords. Once the level has been established, 7 the bony spine lengthens relative to the cord 8 itself. However, Pang has considered that all 9 split cord malformations represent a spectrum 3011 of a single abnormal embryological process 1 [21,22]. This is characterized by the formation 2 and persistence to a variable degree of an abnor- 3 mal connection between the endodermal and 4 ectodermal layers of the embryo, resulting in 5 an endomesenchymal tract. The endomes- 6 enchymal tract results in the independent 7 development of two heminotochords and two 8 hemineural tubes. The degree to which the 9 invading mesoderm (future meninges) is asso- 4011 ciated with the endomesenchymal tract between 1 the two developing neural tubes affects the 2 extent to which the two future hemicords are 3 split. If both hemicords are each surrounded by 4 invading mesoderm, then two separate dural 5 tubes result, with associated bony and fibrocar- 6 tilaginous tissue producing the dividing spur. 7 Pang has termed this the “split cord malfor- 8 mation type I”. If the mesoderm of the future 9 meninges is not associated with the endomes- 5011 enchymal tract dividing the hemicords, then a 1 single dural sac is created, with only thin sagit- 2 tal fibrous bands, representing the remains Fig. 27.3. Lumbar “horse’s tail” in the presence of a split cord 311 of the endomesenchymal tract, attaching the malformation. 483
  10. 10. 484 NEUROSURGERY and this may not be the level of the cutaneous normal lamina and then carrying out a laminec- 1111 stigma (an important point preoperatively), CT tomy of the abnormal lamina below, it usually 2 scanning with intrathecal contrast may demon- being necessary to include the lowermost 3 strate a bony spur. Nevertheless, with modern normal lamina. The spur is then isolated and 4 MRI, CT myelography is generally no longer removed down between the two dural tubes. 5 necessary. The stalk and surrounding epidural veins can 6 Neurological deterioration in split cord mal- bleed briskly and this should be anticipated. 7 formations is generally considered to be a result Once the stalk has been removed, the dura 8 of tethering, although associated lesions such as is opened around the cleft, revealing the 9 hydromyelia may contribute. The aim of hemicords, which usually unite just below 1011 surgery, therefore, is to remove the bony or the location of the spur. Pang emphasizes the 1 fibrocartilaginous spur and to excise the dural importance of dividing any fibrous bands and 2 sleeve surrounding it. In cases with separate median nerve roots, which are non-functioning, 3 dural tubes, each containing a hemicord (type I coursing dorsally to tether the hemicords. These 4 split cord malformations), the tethering spur is bands may continue to the subcutaneous 5 found at the caudal end of the divided dural tissues, forming the entity known as a meningo- 6 tube (Fig. 27.4a). The cutaneous mark may not cele manqué [23]. The dural sleeve around the 7 necessarily lie over the bony abnormality but spur should be excised to ensure that the union 8 there is usually an abnormal lamina present. of the hemicords is free to “ride up”. It is not 9 Surgery involves identifying the lowermost necessary to close the ventral dura but the 2011 1 2 3 4 5 6 7 8 9 3011 1 2 3 4 5 6 7 b 8 9 4011 1 2 3 4 5 6 7 8 a 9 5011 Fig. 27.4. a Type I split cord malformation at operation. The two dural tubes containing the hemicords unite just below the dividing 1 spur, with associated nerve roots visible. b Type II split cord malformation. Two hemicords visible within a single dural tube on CT 2 myelography. The lateral nerve roots are well seen. 311 484
  11. 11. 485 SPINAL DYSRAPHISM 111 dorsal dura may need a patch to obtain satis- There is rarely any neurological deficit, unless 2 factory closure without constriction of the intra- a dermoid cyst has compressed local nerve roots 3 dural contents. Since the hemicords usually or meningitis has caused a deficit. MRI scanning 4 unite below the spur, a single, thickened filum reveals the extent of the tract and any associated 5 terminale may be present. This should be dysraphic abnormality (Fig. 27.5). Contrast 6 sought and divided through a separate incision media or probes should not be inserted along 7 inferiorly, if necessary. the tract. 8 Two hemicords within a single dural tube Surgical excision of the tract is indicated both 9 (type II split cord malformations) generally do because this may be a tethering lesion and 1011 not require surgical exploration unless there is because of the risk of meningitis. This should be 1 evidence of a thickened filum or of dorsal carried out without undue delay. If meningitis 2 intradural fibrous bands (Fig. 27.4b). Pang, occurs, this should be treated as appropriate 3 however, argues that all these malformations first, and only when the inflammation has 4 should be explored since, in all 18 of his resolved should surgery be undertaken. Once 5 reported cases, intradural tethering bands were meningitis has occurred, the tract and sub- 6 found, even in their apparent absence on pre- arachnoid spaces may be scarred, making the 7 operative investigations. This is clearly an area operation technically more difficult. 8 which awaits further clarification. The object of surgery is to excise the tract in 9 its entirety. This involves excising its cutaneous 2011 Congenital Dermal Sinus orifice and following this to its termination. This 1 may require opening the dura and excision 2 Infants are frequently referred to the pediatric of the attachment to the filum terminale. Any 3 neurosurgeon with a midline spinal dimple, associated dermoid cyst, either intradural or 4 occasionally with discharge from the tract. extradural, should also be excised. 5 This may be the initial presentation of many Complete excision achieves a cure and neuro- 6 congenital dermal sinuses but a significant logical outcome is generally very good, with few, 7 number present with meningitis due to skin or if any, long-term problems [24]. 8 gut organisms. Multiple episodes of meningitis 9 may even occur before the diagnosis is made, 3011 since the cutaneous opening of the tract may 1 be minute. Nevertheless, meningitis due to 2 organisms such as Staphylococcus aureus 3 or Escherichia coli in an infant rather than a 4 neonate should arouse suspicion and, particu- 5 larly after recurrent episodes, a concerted effort 6 to identify a sinus tract should be made. The 7 opening may be anywhere along the midline of 8 the spine and may even occur in the occiput. 9 Many infants are referred with a dimple in the 4011 natal cleft, fixed inferiorly. These are generally 1 innocent and should not be explored surgically 2 because of their benign nature and, if surgery 3 is carried out, they almost always become 4 infected. 5 The congenital dermal sinus is an epithelial- 6 lined tract that may end in the soft tissues or 7 may extend deeper, to be attached to or pene- 8 trate the dura; may end in the subarachnoid 9 space; or, more commonly, be attached to 5011 the filum terminale and end at the conus Fig. 27.5. Sagittal T1-weighted MR image of a 14-year-old boy 1 medullaris. There may be inclusion dermoid with a congenital dermal sinus entering the theca at the L4 level. 2 material, forming a mass anywhere along the He had had two episodes of staphylococcal meningitis prior to 311 tract. referral. 485
  12. 12. 486 NEUROSURGERY Neurenteric Cyst established by CT myelography, which will 1111 confirm the connection with the spinal theca 2 Neurenteric cysts are epithelial-lined cysts and reveal the bony anatomy well. MRI scan- 3 derived from the neurenteric canal, which tran- ning will demonstrate the presence of the mass 4 siently connects the embryonic yolk sac with the and its relationship with the pelvic organs, but 5 amniotic cavity during the third week of embry- may not identify the neck of the sac. It is impor- 6 onic development (see “Embryology” section). tant to distinguish these masses from other 7 Due to the endodermal origin of the cyst lining, pelvic masses such as an ovarian cyst or other 8 gastrointestinal or respiratory epithelium may tumor, and, similarly, no attempt should be 9 be found and associated abnormalities of the made to aspirate the cyst through a potentially 1011 gut, respiratory tract and vertebrae may occur. infected area. 1 Such cysts (also called, for this reason, enteroge- Symptomatic cysts are best treated by sacral 2 nous cysts) tend to present as intradural laminectomy, aspiration and ligation of the cyst 3 extramedullary lesions situated ventrally in the neck. If access is not possible posteriorly, an 4 cervical region. They may also be found in the abdominal approach may be indicated, but it is 5 thoracic region, where a dorsal intradural loca- not necessary to excise the meningocele wall. 6 tion is more often seen. Clinically, these lesions Asymptomatic cysts may require no treatment, 7 generally present in adolescence or early adult- although progressive enlargement with time 8 hood with neck pain and spinal cord compres- may be expected. 9 sion, causing a cervical myelopathy. MRI 2011 scanning reveals the cyst and its location, allow- Spinal Dysraphism in Adults 1 ing surgical excision, which can usually be 2 achieved from a posterior approach. Even if a Adult patients with spinal dysraphism include 3 complete excision cannot be achieved safely, those with new symptomatic onset of a previ- 4 due to dense attachments to the cord or ously unsuspected occult dysraphic condition 5 nerve roots, partial excision and cyst drainage and those with a known dysraphic lesion 6 provide lasting benefit, since re-accumulation is in childhood but with symptom onset only in 7 extremely slow. The prognosis for improvement adulthood. In both groups, unlike in childhood, 8 in neurological function is generally very good. pain is the most frequent presenting symptom. 9 This may be poorly localized and bilateral, and 3011 Anterior Sacral Meningocele coupled with weakness in the legs as well as 1 sensory disturbance. Problems with bladder 2 An out-pouching of dura containing CSF may control, as well as erectile dysfunction, also 3 occur through a defect in the body of the sacrum occur frequently. Not infrequently, the problem 4 (anterior spina bifida). This may be an isolated only comes to light as a result of excessive 5 defect or may be in association with a more stretching of the conus, as may occur in child- 6 severe developmental abnormality of the whole birth or trauma [25]. In those with a known dys- 7 caudal region of the embryo, as in caudal agen- raphic lesion, presentation in adulthood may be 8 esis, where abnormalities of the genitourinary with a progressive scoliosis or foot deformity, 9 tract, rectum and anus may also occur in asso- although these features are generally not seen 4011 ciation with sacral agenesis. Presumably, the in an adult with a previously unsuspected 1 defect in the bone is the primary abnormality dysraphism. 2 and, with the pressure of CSF, the meningocele There is often no cutaneous clue to an under- 3 gradually enlarges. The meningocele may lying dysraphic lesion, which may take the form 4 contain sacral nerve roots. As the meningocele of a thickened or tight filum, or an intradural 5 enlarges into the pelvis or retroperitoneal space, lipoma, as well as containing dermoid material. 6 it produces symptoms of compression of the As for childhood dysraphism, surgical 7 pelvic organs, including constipation, urinary untethering is recommended for symptomatic 8 frequency and abdominal or pelvic pain, as well adults. This usually involves division of the 9 as low back pain. Anterior sacral meningoceles filum or release of adhesion and debulking of 5011 are more common in females and may present a lipoma. 1 as an incidental mass identified on pelvic Pang and Wilberger [25] have reported very 2 examination or ultrasound. The diagnosis is satisfying improvements in pain following 311 486
  13. 13. 487 SPINAL DYSRAPHISM 111 surgery in adults, with reasonably good results 6. McLone DG. Continuing concepts in the management of 2 for motor and sensory improvement but, as in spina bifida. Pediatr Neurosurg 1992;18:254–6. 7. McLone DG. Treatment of myelomeningocele and 3 childhood, bladder and bowel dysfunction tends arguments against selection. Clin Neurosurg 1986;33: 4 not to improve significantly with surgery. 359–70. 5 Surgery for fixed orthopedic deformities does 8. Rekate HL. To shunt or not to shunt? Hydrocephalus 6 not improve, although it may prevent progres- and dysraphism. Clin Neurosurg 1984;32:593–607. 7 sive deterioration 9. McAndrew I. Adolescent and young people with spina bifida. Dev Med Chld Neurol 1979;21:619–29. 8 10. McLone DG. Disorders of the pediatric spine. Pang D, 9 editor. New York: Raven Press Ltd, 1995; Chapter 9, 1011 Key Points 137–57. 1 11. Shandling B, Gilmour RF. The enema continence 2 ● The incidence of open myelomeningocele is in catheter in spina bifida: successful bowel management. 3 decline. J Pediatr Surg 1987;22:271–3. 12. Herman JM, McLone DG, Storrs BB, Dauser RC. 4 ● Periconceptual folic acid supplements reduce Analysis of 153 patients with myelomeningocele or 5 the risks of neural tube defects. spinal lipoma reoperated upon for a tethered cord. 6 ● A combined multidisciplinary team approach Pediatr Neurosurg 1993;19:243–9. 7 can lead to a good long-term outlook for 13. Yamada S, Iacono RP, Andrade T, Mandybur G, Yamada BS. Pathophysiology of tethered cord syndrome. 8 patients with open myelomeningocele. Neurosurgery Clin North America 1995;6(2):311–23. 9 ● Midline cutaneous lesions should raise the 14. McCullough D, Levy L, DiChiro G et al. Toward the pre- 2011 suspicion of an underlying occult spinal dys- diction of neurological injury from tethered spinal cord: 1 raphism. investigation of cord motion with magnetic resonance. 2 Pediatr Neurosurg 1990;16:3–7. ● “Tethering” of the spinal cord is considered to 15. Hoffman HJ, Taecholarn C, Hendrick EB, Humphreys 3 be the underlying mechanism for the devel- RP. Management of lipomyelomeningoceles. J Neuro- 4 opment of clinical problems in most occult surgery 1985;62:1–8. 5 dysraphism and the surgical approach to 16. LaMarca F, Grant JA, Tomita T, McLone D. Spinal lipo- 6 mas in children: outcome of 270 procedures. Pediatr treatment, therefore, has been aimed at Neurosurgery 1997;26:8–16. 7 “untethering” the spinal cord. 17. McLone D. Occult dysraphism and the tethered spinal 8 cord. In: Pediatric Neurosurgery, 1999; 61–78. 9 18. Zerah M, Pierre-Kahn A, Catala M. Lumbosacral lipo- 3011 References mas. In: Pediatric Neurosurgery, 1999; 79–100. 19. Pierre-Kahn A, Zerah M, Renier D et al. Congenital lum- 1 2 1. The MRC Vitamin Study Group. Prevention of neural bosacral lipomas. Childs Nerv Syst 1997;13:298–335. tube defects: results of the Medical Research Council 20. Chumas PD. The role of surgery in asymptomatic lum- 3 Vitamin Study. Lancet 1991;238:131–7. bosacral spinal lipomas. Brit J Neurosurg 2000;14:301–4. 4 2. Folic acid and the prevention of neural tube defects. 21. Pang D, Dias MS, Ahab-Barmada M. Split cord malfor- 5 Report from an expert advisory group. Department of mation: Part I: A unified theory of embryogenesis for 6 Health, 1992. double spinal cord malformations. Neurosurgery. 1992 3. Goulding M, Paquette A. Pax genes and neural tube Sep;31(3):451–80. 7 defects in the mouse. In: Boch G, Marsh J, editors. 22. Pang D. Split cord malformation. Part II: clinical syn- 8 Neural tube defects. CIBA Foundation Symposium. drome. Neurosurgery 1992;31:481–500. 9 Number 181. Chichester, UK: John Wiley, 1994; 103–17. 23. James CCM, Lassman LP. Spinal dysraphism: spina 4011 4. Lorber J. Results of treatment of myelomeningocele: an bifida occulta. London: Butterworths, 1972. 1 analysis of 524 unselected cases, with special reference 24. Kanev PM, Park TS. Dermoids and dermal sinus tracts to possible selection for treatment. Dev Med Child of the spine. Neurosurg Clin N America 1995;6(2): 2 359–66. Neurol 1971;18:279–303. 3 5. McLone DG, Dias L, Kaplan WE, Sommers MW. 25. Pang D, Wilberger JE Jr. Tethered cord syndrome in 4 Concepts in the management of spina bifida. In: adults. J Neurosurg 1982;57:32–47. 5 Humphreys RP, editor. Concepts. Pediatr Neurosurg 6 1985;5:97–106. 7 8 9 5011 1 2 311 487