Malformations of the Spinal Cord Dilek Könü-Leblebicioglu, Yasuhiro Yonekawa Core Messages ✔Spinal cord malformations = spinal dysra-phisms are usually diagnosed at birth or early infa
Trang 139 Lowe TG (1987) Double L-rod instrumentation in the treatment of severe kyphosis
second-ary to Scheuermann’s disease Spine 12:336 – 41
40 Lowe TG (1999) Scheuermann’s disease Orthop Clin North Am 30(3):475 – 485
41 Lowe TG, Kasten MD (1994) An analysis of sagittal curves and balance after
Cotrel-Dubous-set instrumentation for kyphosis secondary to Scheuermann’s disease A review of 32
patients Spine 19(15):1680 – 1685
42 MacLean WE Jr, Green NE, Pierre CB, Ray DC (1989) Stress and coping with scoliosis:
psy-chological effects on adolescents and their families J Ped Orthop 9:257 – 61
43 Montgomery SP, Erwin WE (1981) Scheuermann’s kyphosis – Long-term results of
Milwau-kee brace treatment Spine 6:5 – 8
44 Murray PM, Weinstein SL, Spratt KF (1993) The natural history and long-term follow-up of
Scheuermann’s kyphosis J Bone Jt Surg [Am] 75(2):236 – 248
45 Newton PO, Shea KG, Granlund KF (2000) Defining the pediatric spinal thoracoscopy
learn-ing curve Sixty-five consecutive cases Spine 25:1028 – 35
46 Nissinen M (1995) Spinal posture during pubertal growth Acta Paediatr 84:308 – 12
47 Nissinen M, Heliövaara M, Seitsamo J, Alaranta H, Poussa M (1994) Anthropometric
mea-surements and the incidence of low back pain in a cohort of pubertal children Spine
19:1367 – 70
48 Nissinen M, Heliövaara M, Seitsamo J, Poussa M (1995) Left handedness and risk of thoracic
hyperkyphosis in prepubertal school children Int J Epidemiol 24:1178 – 81
49 Noonan KJ, Dolan LA, Jacobson WC, Weinstein SL (1997) Long-term psychosocial
charac-teristics of patients treated for idiopathic scoliosis J Ped Orthop 17:712 – 17
50 Normelli HCM, Svensson O, Aaro SI (1991) Cord compression in Scheuermann’s kyphosis.
A case report Acta Orthop Scand 62:70 – 72
51 O’Brien MF, Kuklo TR, Blanke KM, Lenke LG (2004) Radiographic measurement manual.
Medtronic Sofamor Danek USA, Inc., pp 1 – 110
52 Olafsson Y, Saraste H, Almgren RM (1999) Does bracing affect self-image? A prospective
study on 54 patients with adolescent idiopathic scoliosis Eur Spine J 8:402 – 5
53 Otsuka NY, Hall JE, Mah JY (1990) Posterior fusion for Scheuermann’s kyphosis Clin
Orthop 251:134 – 139
54 Payne WK 3rd, Ogilivie JW, Resnick MD, Kane RL, Transfeld EE, Blum RW (1997) Does
sco-liosis have a psychological impact and does gender make a difference? Spine 22:1380 – 84
55 Ponte A, Gebbia F, Eliseo F (1984) Nonoperative treatment of adolescent hyperkyphosis.
Paper 19th Annual Meeting of the Scoliosis Research Society, Orlando, FL
56 Poolman RW, Been HD, Ubags LH (2002) Clinical outcome and radiographic results after
operative treatment of Scheuermann’s disease Eur Spine J 11:561 – 569
57 Poussa MS, Heliövaara MM, Seitsamo JT, Könönen MH, Hurmerinta KA, Nissinen MJ
(2005) Anthropometric measurements and growth as predictors for low-back pain: a cohort
study of children followed up from the age of 11 to 22 years Eur Spine J 14:595 – 598
58 Reinhardt P, Bassett GS (1990) Short segmental kyphosis following fusion for
Scheuer-mann’s disease J Spinal Disord 3(2):162 – 168
59 Ryan MD, Taylor TKF (1982) Acute spinal cord compression in Scheuermann’s disease.
J Bone Jt Surg [Br] 64B:409 – 12
60 Sachs B, Bradford D, Winter R, Lonstein J, Moe J, Willson S (1987) Scheuermann kyphosis.
Follow-up of Milwaukee-brace treatment J Bone Joint Surg Am 69:50 – 7
61 Schanz A (1911) Schule und Skoliose Kritische Betrachtungen Jahrb f Kinderrheilkunde
73:1 – 26
62 Scheuermann HW (1920) Kyphosis dorsalis juvenilis Ugeskr Laeger 82:385 – 393
63 Scheuermann HW (1921) Kyphosis dorsalis juvenilis Z Orthop Chir 41:305 – 317
64 Scheuermann HW (1936) Kyphosis juvenilis (Scheuermann’s Krankheit) Fortschr Geb
Röntgenstr 53:1 – 16
65 Sörensen KH (1964) Scheuermann’s juvenile kyphosis Munksgaard, Copenhagen
66 Soo CL, Noble PC, Esses SI (2002) Scheuermann kyphosis: long-term follow-up Spine J
2:49 – 56
67 Speck GR, Chopin DC (1986) The surgical treatment of Scheuermann’s kyphosis J Bone Jt
Surg [Br] 68B:189 – 93
68 Stagnara P (1981) Cyphoses dorsales regulieres pathologiques In: SOFCOT – Conferences
d’enseignement 1980 Expansion Scientifique, Paris, pp 51 – 76
69 Stagnara P, De Mauroy JC, Dran G, Gonon GP, Costanzo G, Dimnet J, Pasquet A (1982)
Reciprocal angulation of vertebra bodies in a sagittal plane: Approach to references for the
evaluation of kyphosis and lordosis Spine 7:335 – 42
70 Tallroth K, Schlenzka D (1990) Spinal stenosis subsequent to juvenile lumbar
osteochondro-sis Skeletal Radiol 19:203 – 5
71 Taylor TC, Wenger DR, Stephen J, Gillespie R, Bobechko WP (1979) Surgical management of
thoracic kyphosis in adolescents J Bone Jt Surg [Am] 61A:496 – 503
72 Timm H (1971) Zahl und Ausmass der Kyphosen in verschiedenen Altersstufen Z Orthop
109:927 – 31
Trang 273 Vaz G, Roussouly P, Berthonnaud E, Dimnet J (2002) Sagittal morphology and equilibrium
of pelvis and spine Eur Spine J 11:80 – 87
74 Wenger DR (1993) Roundback In: Wenger DR, Rang M (eds) The art and practice of chil-dren’s orthopaedics Raven Press, New York, pp 422 – 454
75 Willner S, Johnson B (1983) Thoracic kyphosis and lumbar lordosis during the growth period in children Acta Paediatr Scand 72:873 – 78
76 Yablon JS, Kasdon DL, Levine H (1988) Thoracic cord compression in Scheuermann’s dis-ease Spine 13:896 – 98
796 Section Spinal Deformities and Malformations
Trang 3Malformations of the Spinal Cord
Dilek Könü-Leblebicioglu, Yasuhiro Yonekawa
Core Messages
✔Spinal cord malformations ( = spinal
dysra-phisms) are usually diagnosed at birth or early
infancy (open spinal dysraphism, closed spinal
dysraphisms with a back mass) but are
some-times not discovered before adulthood
✔Spinal cord malformations arise from defects
occurring in the embryological stages of
gas-trulation (weeks 2 – 3), neurulation (weeks 3 – 6)
and caudal regression
✔The term “spina bifida” merely refers to a
defec-tive fusion of posterior spinal bony elements
but is still incorrectly used to refer to spinal
dys-raphism in general
✔“Tethered spinal cord” is a broadly used
umbrella term for numerous spinal cord
abnor-malities, such as lipomyelomeningocele,
previ-ously operated on myelomeningoceles, or
thickened filum terminale, which tether (fasten,
fix) the spinal cord in the spinal canal
✔Tethered cord syndrome is a stretch-induced
functional disorder of the spinal cord worsened
by daily, repeated mechanical stretching, and
distortion may even occur in patients who have
the conus at normal level
✔Patients with spinal cord malformation are either diagnosed at birth or present later because of unexplained pain, neurological defi-cits, unclear recurrent urologic infections, cuta-neous markers or orthopedic deformities
✔MRI is the imaging modality of choice and has increased the number of tethered spinal cord diagnoses
✔Prenatal treatment encompasses prophylactic folic acid substitution and intrauterine surgery
✔Open spinal dysraphism is best surgically treated postpartum to untether the spinal cord, prevent infections, repair the dural/cutaneous defect, and restore normal anatomy as far as possible
✔Closed spinal dysraphism with tethered spinal cord warrants early untethering, when mini-mum or mild symptoms are detected
✔Surgery after development of the deficits only stops progression, but symptoms may even fur-ther progress after detefur-thering
✔Individuals with spinal malformations need both lifelong surgical and medical manage-ment, which should be provided by a multidis-ciplinary team
Epidemiology
Myelomeningocele
is the most common form
of open spinal dysraphism
Spine and spinal cord malformations are often collectively summarized under
the term of spinal dysraphisms [39] This term was first employed by
Lichten-stein (1940) [36] Open spinal dysraphism is a common congenital midline defect
of the nervous system and has been historically reported in 2 – 4/1 000 live births
[14] However, the true incidence of spinal dysraphism is not well studied
Myelo-meningocele accounts for the vast majority of open spinal dysraphisms (98.8 %)
[32, 39]
The incidence
of myelomeningocele
is 0.6 per 1 000 live births
Myelomeningocele occurs in 0.6 patients per 1 000 live births, and females are
affected slightly more often than males (by a ratio of 1.3 to 3), with the first-born
usually affected [5, 39] Myelocele is a rare malformation and represents only
1.2 % of all open spinal dysraphisms [39] The most common locations for these
malformations are, in decreasing frequency, lumbosacral, thoracolumbar and
Trang 4a b
c
Case Introduction
A 17-year-old patient presented with progressive tethered
cord syndrome with worsening of hand functions and
some leg weakness and increasing spasticity Postnatally
he had had a cervical myelomeningocele and had had
only “cosmetic” closure after the birth The MRI showed a
widened spinal canal at C6–C1 (a,c), cord tethering
dor-sally at C6 – 7 and dorsal limited myeloschisis It is possible
to see the hypotrophic right hand (b) This clinical
worsen-ing recovered after an intradural exploration and
dissec-tion of the stalk placode.
cervical spine [5, 39] The incidence of myelomeningocele varies from country to country and from one geographical region to another [20] Since the early 1980s, estimation of the prevalence of open spinal dysraphism in many industrialized countries has been decreased by folic acid administration to pregnant women and the availability of prenatal diagnosis and elective termination [20, 29, 48] Patients with open spinal dysraphism almost always have associated Chiari II malformation There are also reports in the medical literature of an association between closed spinal dysraphisms and Chiari II [41]
Spina bifida is present
in 90 – 100 % of patients
with tethered cord
Spina bifida occulta occurs in approximately 17 – 30 % of the total population
and is present in 90 – 100 % of patients with tethered cord [35, 61] The dermal sinus is a common abnormality and accounts for 23.7 % of all closed spinal dysra-phisms Overall, caudal regression syndrome is not uncommon, accounting for
798 Section Spinal Deformities and Malformations
Trang 516.3 % of all closed spinal dysraphisms Sacral agenesis occurs in approximately
one per 7 500 births without a gender predisposition
The conus normally terminates at L2
In the normal adult population the conus terminates at L2 in 95 % of cases [19,
48] In its classical form, tethered cord implies a low-lying conus, but tethered
cord syndrome may occur in the presence of a conus in normal position [19, 37,
40, 46, 48, 54, 56] Up to 15 % of patients with repaired myelomeningoceles will
experience a secondary tethered cord syndrome later in life [36]
Pathogenesis
Embryological Aspects
Knowledge of normal embryology is essential for the understanding of the
path-ogenesis and a wide spectrum of pathoanatomy of spine and spinal cord
anoma-lies as well as tethered cord The most comprehensive embryonic staging system
is that of O’Rahilly [23] and most of the information on early human
develop-ment has been obtained through study of the Carnegie collection [23] Early
neu-ral development has been reviewed in various basic science articles [21]
O’Rahilly provides a timetable for each important event in early neural
morpho-genesis: the embryonic period begins at conception with stage 1 and ends at
stage 23 Beyond this time, the developing human enters the fetal period [6, 23]
(Table 1)
Table 1 Human embryogenesis
Weeks Days Carnegie
stage
Process Size (mm) Somite
number
Events
Embryonal
period
Week 1 1 1 fertilization 0.1 – 0.15 fertilized oocyte, pronuclei
2 – 3 2 cleavage 0.1 – 0.2 cell division with reduction in cytoplasmic
volume, formation of inner and outer cell mass
4 – 5 3 blastula 0.1 – 0.2 loss of zona pellucida, free blastocyst
streak
Week 3 15 – 17 7 gastrulation 0.4 gastrulation, notochordal process
17 – 19 8 neurulation 1.0 – 1.5 primitive pit, notochordal canal
19 – 21 9 somatization 1.5 – 2.5 1 – 3 neural folds, cardiac primordium, head
fold
Week 4 22 – 23 10 2 – 3.5 4 – 12 neural fold fuses
23 – 26 11 2.5 – 4.5 13 – 20 rostral neuropore closes
26 – 30 12 3 – 5 21 – 29 caudal neuropore closes
Week 5 28 – 32 13 organogenesis 4 – 6 30 leg buds, lens placode, pharyngeal arches
35 – 38 15 7 – 9 lens vesicle, nasal pit, hand plate
Week 6 37 – 42 16 8 – 11 nasal pits moved ventrally, auricular
hillocks, foot plate
Week 8 51 – 53 20 18 – 22 upper limbs longer and bent at elbow
Fetal
period
Week 9 56 – 60 23 phenogenesis 27 – 31 rounded head, body and limbs longer
Trang 6Relevant Embryogenetic Steps Spinal cord embryological development occurs through three consecutive
peri-ods [11, 19, 26, 39, 48, 58]:
Gastrulation
The trilaminar embryo develops by day 18 of gestation At this point, the embryo
is composed of endoderm, mesoderm and ectoderm Shortly thereafter, the mesoderm releases factors which induce the differentiation of the overlying neu-roectoderm, thereby forming the neural tube
Neurulation
After gastrulation the ectoderm above the notochord folds to form a tube, the neural tube; this gives rise to the brain and the spinal cord, a process known as
neurulation Primary neurulation (weeks 3 – 4): The process of fusion begins in
the region of the lower medulla and proceeds rostrally and caudally The anterior neuropore closes at about 24 days and the posterior neuropore at 26 – 28 days The brain and the spinal cord are formed by primary neurulation, which involves the shaping, folding, and midline fusion of the neural plate It is completed about the 25 – 26th day of conception The central canal is formed and is lined by epen-dyma The caudal cell mass, a group of undifferentiated cells at the caudal end of the neural tube, develops vacuoles These vacuoles merge together and expand, ultimately meeting the central canal of the rostral cord and causing elongation of
the neural tube in a process called canalization Secondary neurulation and
ret-rogressive differentiation (weeks 5 – 6) results in formation of the conus tip and
Filum terminale and conus
medullaris are formed
during the process
of neurulation
filum terminale The formation of the lower lumbar, sacral, and coccygeal por-tions of the neural tube are by canalization and retrogressive differentiation Overlapping with canalization, the process of retrogressive differentiation of the caudal cell mass takes place In this process, the filum terminale, conus medulla-ris, and ventriculus terminalis are formed
Caudal Regression
The conus medullaris
ascends during spinal
growth
At the time when the neurulation process is complete (weeks 6 – 7), the terminal filum and cauda equina are formed from the caudal portion of the neural tube by
regression The conus medullaris initially rests in the coccygeal region and
appears to ascend as the spine grows more rapidly than the cord At birth the conus is usually at the caudal level of L2 – L3 and by 3 months of age it is at L1 – L2, where it remains (relative ascent of the spinal cord) The spinal cord terminates
at or above the inferior aspect of the L2 vertebral body in 95 % of the population and at or above the L1 – L2 disc space in 57 % of the population The conus medul-laris has reached its mature adult level at term in most infants and 100 % of cases
at approximately 3 months after full-term gestation [39, 48, 58] The conus medullaris initially rests in the coccygeal region and appears to ascend as the spine grows more rapidly than the cord At birth the conus is usually at the caudal level of L2 – L3 and by 3 months of age it is at L1 – L2, where it remains
Interference with normal development at any stage is responsible for the
vari-ous abnormalities seen in the cases of spinal malformations [19, 26, 38, 39, 58]
(Table 2)
800 Section Spinal Deformities and Malformations
Trang 7Table 2 Embryological classification of spinal dysraphisms
Gastrulation Notochordal integration ) neuroenteric cysts and fistula
) split cord malformations (diastematomyelia, diplomyelia)
) dermal sinus, fistula
) dermoid/epidermoid tumors Notochordal formation ) caudal regression syndrome
) segmental spinal dysgenesis
) myelocele
) lipomyelomeningocele
) lipomyeloschisis
) intradural spinal lipoma Secondary neurulation ) tight filum terminale, filum terminale lipoma
Canalization
Retrogressive differentiation ) intrasacral meningocele, sacral cysts
Risk Factors
Most spinal cord anomalies result from a complex interaction between several
genes and poorly understood environmental factors A list of variables have been
implicated as risk factors for spinal dysraphisms but only a few have been
estab-lished
Genetic Factors
Family history is an important risk factor
Spinal cord anomalies occur in many syndromes and chromosome disorders
However, a spinal dysraphism may be the only anomaly in a member of a family,
in which case the relatives have an increased risk for all types of tethered cord A
family history is one of the strongest risk factors [20, 26]
Environmental Factors
Periconceptual folic acid substitution reduces the incidence of neural tube defects
Periconceptual multiple vitamin supplements containing folic acid reduce the
incidence of neural tube defects In England and the United States, it is
recom-mended that women planning pregnancy take 0.4 mg folic acid daily before
con-ception and during the first 12 weeks of pregnancy [14, 44] Up to 70 % of spina
bifida cases can be prevented by periconceptional folic acid supplementation [20,
26]
Maternal Diabetes
Pre-gestational diabetes
is a risk faktor for spinal malformation
In women with pre-gestational diabetes, the risk of having a child with a central
nervous system malformation (including spinal malformations) is twofold
higher than the risk in the general population [20]
Medication
Valproic acid or carbama-zepine increases the risk
of spinal malformation
Some drugs taken during pregnancy may increase the risk These include sodium
valproate and folic acid antagonists such as trimethoprim, triamterene,
carb-amazepine, phenytoin, phenobarbital and primidone [20]
Trang 8Pathophysiology of Tethered Cord Syndrome
Tethering of the spinal cord
results in progressive
neurological deficits
Tethered cord is a spinal cord malformation in which the spinal cord is fixed in an abnormally low position and in a relatively immobile state [2, 19, 39, 46, 58] In this context, the term “tether” refers to “fasten” or “restrain” Tethered cord exists
in open and occult forms of spinal dysraphisms [15, 48] The normal spinal cord
is free, i.e it is not attached to any surrounding structures in the spinal canal except for denticulate ligaments and nerve roots A tethered cord is tightly fixed
so that there is not a normal movement of the spinal cord During the formation
of the embryonic spinal cord, it fills the entire length of the spinal canal As the fetus grows, the vertebral column grows faster than the spinal cord Thus, the dis-tal end of the spinal cord is located at the level of the first or second lumbar verte-bral body (L1 – L2) If there is an abnormality affecting this “ascension” of the spi-nal cord (e.g myelomeningocele, tight filum termispi-nale, diastematomyelia, sec-ondary scar formations, tumors), the spinal cord is tethered [50] This results in stretching of the spinal cord and causes neurological damage even during the fetal period By the time a child is born, the spinal cord is normally located between the first or second lumbar vertebral body After birth, continuing growth puts further stretch on the tethered spinal cord; this damages the spinal cord both by directly stretching it, and by interfering with the blood supply and oxidative metabolism [51]
A tethered cord can occur even with
a normal level conus
If neurological findings are already present the further clinical deterioration can be anticipated Since an adult spine is no longer growing, children are obvi-ously more at risk than adults However, even adults with tethered cord can show deterioration This is due to daily repetitive-cumulative stretching on the teth-ered cord A sudden flexion movement of the spine can also produce symptom-atic onset of the tethered cord syndrome [9, 51] Irreversible neuronal damage can occur when there is sudden stretching of the already chronically tethered conus [51] Yamada and coworkers have nicely demonstrated changes in spinal cord blood flow and oxidative metabolism following tethering of the spinal cord
A tethered cord can occur
with the conus at a normal level
both in experimental animals and humans [9, 51, 52, 55, 58] Usually a tethered cord results in a low conus position However, there are many cases of tethered cord syndrome reported with the conus at a normal level [37, 40, 46]
Terminology and Classification
Spinal cord malformations can be categorized as:
) open spinal dysraphisms
) closed (occult) spinal dysraphism
Open spinal dysraphism is characterized by exposure of the abnormal spinal
nervous tissue and/or meninges to the environment through a bony and skin defect Open spinal dysraphism basically includes myelocele and
myelomeningo-cele In closed spinal dysraphism, there is no exposure of neural tissue (covered
by skin) However, some kind of cutaneous stigmata, such as hairy patch, dim-ples, or subcutaneous masses, can be recognized in up to 50 % of closed forms [15, 32, 47]
Spina bifida results from a defective fusion of posterior spinal bony elements
and leads to a bony cleft in the spinous process and lamina (L5 and S1) The term has incorrectly been used to refer to spinal dysraphism in general [32, 39] The
terms spina bifida aperta or cystica and spina bifida occulta were used to refer
to open spinal dysraphism and closed spinal dysraphism, respectively These terms have been progressively discarded [32]
802 Section Spinal Deformities and Malformations
Trang 9Table 3 Chiari malformations
Type 1 ) caudal displacement of the cerebellum
) cerebellar tonsils below the plane of the foramen magnum
) no involvement of the brainstem
) associated with occult spinal dysraphism (e.g spinal lipomas)
) note – cerebellar ectopia can be a normal finding (up to 5 mm)
Type II ) small and crowded posterior fossa
) caudal displacement of the fourth ventricle and medulla into the upper
cervical canal
) tonsils can be at or below the level of the foramen magnum usually
) association with a variety of cerebral anomalies frequently associated with
myelomeningoceles
Type III ) displacement of the posterior fossa structures into the cervical canal (seldom
compatible with life)
Type IV ) cerebellar hypoplasia without herniation
Placode (neural placode) is a segment of non-neurulated embryonic neural
tis-sue It is in contact with air in open spinal dysraphism and covered by the
integu-ment in closed spinal dysraphism A terminal placode lies at the caudal end of
the spinal cord and may be apical or parietal depending on whether it involves
the apex or a longer segment of the cord A segmental placode may lie at any level
along the spinal cord [32, 39]
Differentiate hydromyelia from syringomyelia
Hydromyelia is the simple dilatation of the central canal and is lined by the
ependyma An extension into cord parenchyma constitutes a true syringomyelia.
Two forms of syringomyelia can be differentiated:
) communicating syringomyelia
) non-communicating syringomyelia
Communicating syringomyelia is related to a primary dilatation of the central
canal and is usually associated with abnormalities of the craniocervical junction
(e.g Chiari malformations) Non-communicating syringomyelia may result
from trauma, tumors or inflammation and does not communicate with the
cen-tral canal or the subarachnoidal space
Chiari malformations are hind brain abnormalities and are observed in
con-junction with spinal cord malformations They are categorized into four types,
with Types I and II accounting for 99 % of the clinical cases (Table 3)
Classification of Spinal Malformation
From a clinical perspective, a practicable classification system of spinal cord
anomalies is needed However, the large variety of features associated with these
anomalies makes such classification difficult Classical classifications rely on the
embryological development cascade [11, 19, 22, 39, 58] (Table 4) We find the
mixed clinical-neuroradiological classification system presented by Donati et al
[5, 32, 39] useful
From the clinical perspective, a question framework to approach the
spec-trum of spinal cord malformation is useful:
) Is there a back mass?
) Is it covered with skin?
) Are there cutaneous markers?
) Is there a tethered cord syndrome?
Trang 10Table 4 Classification of spinal malformations
Spinal malformations with back mass
Open spinal dysraphism With a non-skin-covered back mass (spina bifida aperta)
Chiari II malformation
) myelocele (myeloschisis) Closed (occult) spinal
dysraphism
With a skin-covered back mass (spina bifida cystica)
) meningocele (posterior)
) myelocytocele
) lipomyelomeningocele/lipomyeloschisis
Spinal malformations without back mass
) spinal lipoma (intradural and/or intramedullary)
) anterior sacral/lateral thoracic meningocele
) tight filum terminale/filum terminale lipoma
) dermal sinus, fistula, dermoid/epidermoid tumors
) neuroenteric/bronchogenic cysts and fistula (split notochord syndrome)
) split cord malformations (diastematomyelia, diplomyelia)
) caudal regression/agenesis
) intrasacral meningocele/sacral cysts
) neuroectodermal appendages
Myelomeningocele and Myelocele
Myelomeningoceles and myeloceles are characterized by exposure of spinal intradural elements through a midline defect to the air The basic defect of mye-lomeningocele is caused by an abnormality, which occurs at the stage of neurula-tion that prevents the neural tube from closing dorsally [5, 19, 22, 27, 39] A mye-lomeningocele consists of a sac of exposed neural tissue-placode, which is clef-ting dorsally, splayed open and herniates through a large dysraphic defect through the bone and dura beyond the surface of the back The cord is tethered
posteriorly at this level In myelocele (synonym: myeloschisis), however, the
neu-ral placode is flush with the plane of the back and identifiable on the surface All children with myelomeningocele have tethered cord from the time of birth One can easily visualize how tethering of the spinal cord might occur (Case Study 1) Patients with myelomeningocele and myelocele almost always (75 – 100 %)
have associated Chiari II malformation ( Table 3) [5, 14, 20, 32, 39] Distortion and maldevelopment of the medulla and midbrain can cause lower cranial nerve palsies and central apnea (which may be misdiagnosed as epilepsy) [44] Patients with
myelo-meningocele and myelocele
almost always have
associated Chiari II malformation
Hydrocephalus may be present at birth, but usually appears within 2 – 3 days after surgery [14, 32, 45] The rate of hydrocephalus in patients with occult spi-nal dysraphism has been reported to be over 80 % [14, 43] Hydromyelia may occur in as many as 80 % of these patients, and may be localized or extend through the whole cord It may cause rapid development of scoliosis if left untreated [18, 29, 32]
Meningocele
The posterior meningocele consists of a herniated sac of meninges with CSF
protruding from the back and covered with skin It is commonly lumbar or sacral
in location, but thoracic and even cervical meningoceles may be found The spi-nal cord and conus are seen in the normal position [5, 32, 39], although both nerve roots and, more rarely, a hypertrophic filum terminale may course within the meningocele No part of the spinal cord is contained within the sac by defini-tion [5] The spinal cord itself is completely normal structurally, although it is usually tethered to the neck of sacral meningoceles [39] A Chiari II
malforma-tion is found only excepmalforma-tionally Anterior meningoceles are typically presacral,
804 Section Spinal Deformities and Malformations