is the commonest of neural
tube defects. Spina bifida occulta
is much more prevalent than open variety. It is a failure of fusion of the
vertebral arches, most frequently the fifth lumbar and first sacral, without a
protrusion of the cord and meninges. It may involve only one vertebra or may
extend over several segments. It is seen as an incidental X-ray finding in 17-30
per cent of the normal population.
For the majority it carries no clinical
significance but an occasional patient may have an occult spinal dysraphism in
the form of a tethered cord, midline spur, lipoma, dermoid or an abnormal
dilatation of the sacral end of the dural sac (occult intrasacral meningocoele).
The overlying skin may be normal or stigmata of adysraphic state, such as
hypertrichosis, haemangioma, skin pigmentation, dimples, sinuses and "pedunculated
tail" may be present.
be collectively called 'Tethered cord syndrome.
neurological deterioration localized to the lower spinal cord resulting from
traction on the conus medullaris has been termed TCS. Tethered cord is
associated with low conus below the mid L2 level and a short, thick filum,
attached to the dura, or an extradural band may anchor the cord. It is the cord
which is tethered, with the nerve roots lying lax and even loosely on either
side. The effects of the tethering is maximum close to the site of tethering and
when the tethering lesion extends over a distance the maximum effect is on the
cord adjacent to the caudal end of the lesion, where the maximum stress lies.
Any process that
tethers the spinal cord can result in a patient who has tethered cord syndrome.
Children can be born with normal anatomy and develop a tethered cord
(secondary) through an acquired process, such as infection, scarring, or tumor.
This section focuses on congenital (primary) causes of tethered cord.
Lipomyelomeningocoele and a thickened filum terminale accounts for 70 per cent
simplest form of conditions causing TCS. In this condition, the filum terminale,
can be thickened, potentially with lipomatous tissue. Hoffman and colleagues
have suggested that a diameter of 2 mm or greater should be considered an
abnormally thickened filum. Impaired canalization of the growing secondary
neural tube (the neural cord) with cells capable of growth and differentiation,
particularly preadipose tissue, is believed to be the cause of both the
thickened and fatty filum terminale. The fatty filum commonly is associated with
cases of imperforate anus, suggesting a common timing of pathogenesis during
are more extensive lesions and represent a combination of a splayed cord fused
with a lipomatous mass, which in turn fuses with the subcutaneous adipose
tissue. The neurologic deficits of cord tethering are probably caused by
impaired circulation in the stretched cord, as evident by its reduced oxidative
metabolism or to abnormal development as the cause of the neurologic deficits as
An intradural lipoma
has no anatomic connection with the subcutaneous fat and lies wholly within the
dural space in embryologic terms. This is similar to a lipomyelomeningocele
except that the neural tube closes after
tethering due to lipoma
the mesenchyme has entered. In some
patients, the cord is bound down by lipomatous tumors or fibrous tissue, the
sacral roots ascending. Lipomas may attach dorsally to the conus and be sessile
or pedunculated, while other lipomas occupy the distal end of the conus,
elongating the latter and terminating in a small lipoma with attached nerve
roots. The dorsal and caudal lipomas may occur in combination. Filar lipomas
occupy an enlarged filum terminale. Lipomas most are commonly subpial, although
a small number can be subdural. Subdural lipomas are infrequently associated
with tethering and more commonly present like a mass lesion with cord
compression. More commonly, however, lipomas of the spinal cord occur in the
lumbosacral region and have an associated dural defect.
Dorsal dermal sinus
is a long, thin, squamous epithelium-lined sinus that extends from the skin
surface for a variable distance. Like most dysraphic abnormalities the commonest
sits for the defect is the region of the posterior neuropore i.e.the lumbo-sacral
region, the next frequent site being the sub-occipital region. It may, however,
occur anywhere in the dorsal midline from the nasion to the coccyx. It may
rarely be away from the midline. The sinus may terminate extradurally,
intradurally or extend into the fourth ventricle or the medulla where it may
produce an abscess or a dermoid. The defect arises as a result of failure of
separation of the neuroectoderm from the epithelial or surface ectoderm. This
separation normally takes place between the 3rd-5th week of intrauterine life.
The congenital dermal sinus is mostly superficially located and presents as a
dirnple. This sinus may become symptomatic due to an infection if it has a
connection within the theca, distorts growth of the neural tissues or
compression of neural tissue if associated with a dermoid/epidermoid.
Meningitis is the
most common presentation. The cutaneous opening may at times be inconspicuous
with surrounding hairy growth, naevus, pigmentation or lipoma, When infected,
the opening of the sinus becomes red and inflamed with erythema of the
surrounding skin. A clinical picture of spinal arachnoiditis may be seen as a
result of recurrent attacks of subclinical infection. Any or all the
neurological features observed in spinal dysraphism may be encountered in this
condition. Spinal compression, extradural, intradural or intramedullary, may be
caused by an associated dermoid or epidermoid cyst or by a secondary localised
abscess. The neurological level of the lesion is usually several segments
higher than the external opening, as the dermal sinus runs an oblique course
from the skin in a cephalad direction.
malformation (SCM) results from abnormal splitting of the notochord. This new
nomenclature was introduced by Pang, et al., in 1992, to eliminate confusion
created by the use of the terms diastematomyelia and diplomyelia.
Diastematomyelia usually refers to a split cord in which the two halves are
separated by a bone spicule and contained within separate dural sleeves. In
contrast, the term diplomyelia is generally used to describe a condition of two
hemicords within one dural sac, often with two complete sets of nerve roots,
separated by a fibrous band. Pang, et al., proposed a common origin of both
malformations: an adhesion between the ectoderm and endoderm leads to an
endomesenchymal tract that bisects the spinal cord. If the tract also contains
cells of the precursor cells of the meninges (meninx primitiva) the resultant
malformation would be SCM Type I, or diastematomyelia. Otherwise, the formation
of a separate dural sleeve and bone septum does not occur, and the malformation
is a SCM Type II, or diplomyelia.
In both SCM I and SCM
II, when neural crest cells are also involved in the split, two sets of dorsal
roots will develop with each hemicord having paramedian dorsal roots as well.
These rootlets may end blindly at the midline septum or go beyond the dura along
with a leash of abnormal vessels and fibrous tissue to form the fibroneuro
vascular stalk of a myelomeningocoele plaque. The endomesenchymal iract may
persist to a variable extent. When it goes upto the cutaneous ectoderm, it may
form a fine dermal sinus or a wide myelomeningocoele. It may differentiate to
form the various cutaneous stigmata, lipoma, dermoid or epidermoid cysts. In a
type ll SCM the fibrous septum may be entirely ventral to the cord, with the
dorsal surface of the cord looking normal.
The common site of
this defect is the lower thoracic or lumbar region. When the lesion is situated
in the lumbar region the cleft often is through an unusually low placed conus.
Both types of SCMs
represent lesions that tether the spinal cord during growth and movement. The
lesion manifests itself commonly in children, with a higher incidence in
females. Occasionally cases presenting with symptoms in adult life have been
reported. The development of symptoms and signs appears to be related to periods
of rapid skeletal growth. Prevention of the normal ascent of the cord by the
spur during these periods has been blamed for the development of the
neurological deficit. It is the spur and not the divided cord that is the cause
of the symptoms.
variant of hydromyelic dilatation of the central canal, the cystic cavity being
within the cord and the spinal roots originating at the ventral and dorsal outer
surface of the cyst wall. A myelocystocele is often associated with defects of
the vertebral bodies or intestinal fistula. These types of lesions are often
located in the cervical or upper thoracic cord at the level the underlying bony
defect. They often are associated with a lipoma (lipomyelocystocele).
often are found on the ventral side of the spinal canal and consist of a
fluid-filled cyst that may communicate with the gastrointestinal tract through a
vertebral defect such as a hemivertebra or butterfly vertebra. The neurenteric
cyst itself can cause compression, but its adherent fibrous bands also can
result in tethering.They usually are intradural and extramedullary, and their
origin is debated, although positive immunoreactivity for carcinoembryonic
antigen suggests endodermal origins.
Tethering can occur
with meningocele and meningomyelocele, as functional cord attaches itself
dorsally either to dura or to surface ectoderm. An interesting case of
meningocele known as the "meningocele manque" (the "missing" meningocele) occurs
when a meningocele has formed during embryogenesis but has healed spontaneously
or scarred creating a dorsal band. These dorsal bands can extend from
intrathecal structure into the dura or outside structures creating a significant
tethering effect . The dorsal band of meningocele manque may reflect a
fibroneurovascular stalk derived from the same endomesenchymal tract that is
the basis for split cord malformations.
meningocoeles are rare lesions and may occur in the pelvis through a defect in
the sacrum, the meninges may protrude into the pelvis causing compression of the
pelvic organs or the condition may present as a neurogenic bladder. The sac may
harbor benign tumors like a lipoma and the filum terminale attached to the
meningocoele may produce a tethered cord syndrome. Intrathoracic meningocoeles
are often associated with neurofibromatosis and are frequently confused with
mediastinal tumors. However, meningocoeles cause fewer physical signs than
tumors. X-rays of the spine often show erosion of the posterior aspect of the
dorsal vertebrae. These meningocoeles are best left alone except when there are
compelling reasons forcing surgery.
presentations differ widely in children and in adults. Rapid early deterioration
within the first weeks after birth characterises those lesions associated with
imperforate anus, omphalocoele and exstrophy. The onset of tethered cord
syndrome is related to the level of the pathology and the height and age of the
Pain is invariably
present in the adult as a diffuse, dysaesthetic "central'' type of pain over the
legs and perineum and in some patients may mimick a lumbo-sacral intervertebral
disc protrusion. In chidren pain is uncommon feature and is limited to the
A slow onset of
difficulty in micturition or a limping gait in a child seven or eight years old
or more, should arouse the suspicion of a tethered cord.
Cutaneous stigmata of
dysraphism are almost always present in a child while only about half the adults
have them. They include the midline lumbosacral cutaneous hemangiomas,
lumbosacral hypertrichosis, the lumbosacral dermal sinus, the midline
lumbosacral subcutaneous lipoma, and the lumbosacral skin appendage. The
cutaneous stigmata are present in approximately 50%70 of patients who present
The hallmark of the
neurological deficits is their asymmetry. Sensory, motor and bladder involvement
are frequently seen in children as well as adults. Neurological deterioration
with both upper and lower motor neuron involvement takes months or years and
symptoms appear during late childhood. In children motor involvement is in the
form of gait disturbance and in the adult there is actual weakness and wasting.
Bladder symptoms in
the form of incontinence or repeated bouts of urinary tract infection may be the
only symptom. Orthopedic deformities such as scoliosis or kyphoscoliosis is
common. There may also be deformities of the feet, e.g., pes cavus, talipes
equinovarus or trophic skin lesions. They are in adults.
are almost always abnormal. There is usually a spina bifida, a circumscribed
median bony opacity, a widening of the interpedicular distance or an associated
hemi-or block vertebra.
MRI is well suited to
identifying the level of the conus relative to vertebral bodies, the presence of
a syrinx, or visualization of other pathologic processes. MRI also is able to
define the anatomy of other causes of tethered cord, such as the anatomy of
terminal or multiple lipomas, the presence of congenital lesions (such as
dermoids), and the presence of myelomeningocele. Its limitation, however, is the
poor quality of images in infants, the difficulty in interpreting the various
aspects of a complex malformation, and its inability to define bony ventral
abnormalities like the bony septum in a split cord malformation.
can have a role as a relatively quick and easy screening tool in young children.
progression of symptoms in patients who have a tethered cord often calls for an
untethering operation. Patients who have large spinal lipomas that exhibit mass
effect on the spinal cord, and presenting only with pain may be considered for a
trial of weight loss before committing to surgical intervention.
A group of
myelomeningocele patients who have symptoms suggestive of tethered cord syndrome
and who also have ventricular shunts. A malfunctioning shunt sometimes can cause
signs and symptoms that may mimic a tethered cord, and shunt correction helps.
Orthopedic deformities may be the presenting symptoms, and untethering should
be considered before orthopedic correction. data suggest that the neurosurgeon
should recommend untethering as treatment of the root cause of scoliosis in
selected cases, but that correction of the deformity may be limited, and
orthopedic involvement may be necessary.
still surrounds treatment options for the asymptomatic patient who has signs of
a spinal anomaly, particularly a milder anomaly such as a thickened filum or an
asymptomatic lipoma. The risks must be weighed, because lipomas of the filum
(or a thickened filum) have much better surgical outcomes than more complex
ones. Some recommend surgical prophylactic untethering in asymptomatic group,
since surgery does not always provide a reversal of dysfunction or abnormality
in symptomatic patients.
can arrest the progression of symptoms in the majority of patients; a smaller
percentage of patients show improvement after untethering. Improvement is more
likely to be seen in patients whose primary symptom is pain, although these
patients tend to be an older population including young adults and adults.
Finding of a normal
bony lamina may allow identification of the dura and subsequent improved
understanding of abnormal tissue planes. This principle holds true intradurally
as well, where rostral exposure of normal spinal cord may facilitate safer
dissection. Use of laser, if available, helps in complex cases, such as, a
neurophysiologic monitoring with combinations of motor-evoked potentials and
sensory-evoked potentials helps in identifying nerve roots.
The filum is
recognizable by its fatty appearance, by its straight midline location, and by
its vasculature. It is important to visualize the underside of the filum
before sectioning, because nerve roots can travel along with the filum. Once
the filum is sectioned, care should be taken that there is no bleeding at the
site of section before the proximal stump is released, because it may retract
out of reach.
In split cord
malformations, once the median spur/septum is removed, the dural sleeves of both
hemicords are opened, and the median dura is resected along with the ventral
dura with no ventral repair.
Dermal sinus tracts
should be explored intradurally and excised in toto. Simple excision of the
extradural component of the tract may not alleviate intradural tethering.
As much of any
intradural lipoma or dermoid is excised as is safely possible. It is not
desirable to embark upon a hazardous total excision especially in the caudal and
transitional variant of lipomyelorneningocoele. The lipomas dissected all around
under the operating microscope, defining its neck in the lumbo-dorsal fascia.
The normal dura under the laminectomy is opened and extended inferiorly dividing
the constricting fibro vascular band lying around the dura just inferior to the
last intact lamina. The band is frequently seen in the dorsal variant and its
division leads to an immediate ballooning of the released dura. An associated
congenital dermal sinus or split cord malformation is treated. Likewise any
intraspinal meningocoele may have to be excised before opening the dura. On
opening the dura, extreme care is required to preserve sensory nerve roots that
may be adherent to the dura. Careful dissection using magnification and bipolar
stimulation is required to identify and excise the filum terminale to release
the tethered cord. As this is being done one may notice an actual cephalic
migration of the cord and a change in the direction of the nerve roots.
often are extremely adherent to the spinal cord and, because of the risk of
recurrence, should be resected completely if possible. This may require a
A watertight dural
closure, with graft if necessary, is mandatory. To avoid retethering, meticulous
attention is needed in hemostasis and closure. Dural closure with 4-0 Nurolon is
adequate for many straightforward detethering operations. With more complex
spinal dysraphisms, a running monofilament suture can be used with good results.
In complex lesions, such as extensive lipomas, resection of the maximal amount
of pathologic tissue should be performed, followed by imbrications of the pial
surface to create a smooth surface apposed to the dura.
In severe cases of
retethering in patients who have myelomeningocele and compromised neural
function, transaction of the spinal cord above the neural placode can be
performed to prevent the placode from scarring and forming adhesions. Post
operatively, patients are nursed prone to minimize adhesions of the cord to the
dural suture line. The patients are turned supine and slowly elevated in bed
over several days.
Retethering is about
20% in complex cases. Complete hemostasis at surgery, imbrications of the pial
surface to create a smooth surface apposed to the dura, and nursing patients in
prone position postoperatively help in preventing retethering. Any new or
significantly progressive orthopedic, urologic, or neurologic symptom should be
evaluated for the possibility of retethering. Although retethering can occur at
any time, the risk often decreases once adult stature is reached and growth has
stopped. Resurgery may be considered.