Neurofibromatosis is a multisystem disease that primarily affects cell
growth of neural tissue. The intent of this article is to identify the spinal
complications in skeletally immature patients that are most commonly
associated with neurofibromatosis and to present strategies for
management.
Café au Lait Spots
Café au lait spots are present in more than 90% of all
patients with NF1. The pigmentation is tan, macular, and melanotic in origin
and is located in and around the basal layer of the epidermis; the lesions may
vary in shape, size, number, and location. In relation to NF1, these spots are
frequently found in areas of the skin that are not exposed to the sun. Some
patients may have very large café au lait spots that involve a
large segment of the body, including a "bathing trunk"
distribution.
Axillary and Inguinal Freckling
Freckles—diffuse, small, hyperpigmented spots as much as 2 to 3 mm in
diameter found in the axillary and inguinal region and other skin folds (areas
not usually exposed to sunlight)—are helpful diagnostic criteria for
NF1.
Lisch Nodules
Lisch nodules, or pigmented hamartomas of the iris, are present in 94% of
patients with NF1 who are six years of age or older; 28% of younger patients
have them12. They
increase in number with age, but they do not become symptomatic. The lesions
appear to be specific for NF1; they are not commonly seen in non-NF1
individuals.
Neurofibromas
Neurofibromas mostly involve the skin, but they may be seen in deeper
peripheral nerves. They may be nodular and discrete or diffuse with
interdigitation with surrounding tissues. Highly vascular plexiform
neurofibromas may cause segmental or localized hypertrophy. Puberty or
pregnancy may cause an increase in the size and number of the
lesions13.
Cutaneous Neurofibromas
Cutaneous neurofibromas, formerly called fibroma molluscum, are present in
subcutaneous tissues and are typically found after puberty. They are usually
manifestations of longstanding or adult disease and occur with low frequency
(12%) in childhood. Recent electron microscopy studies have demonstrated that
axons and Schwann cells are present in these tumors; therefore, it is
appropriate that they be called dermal neurofibromas.
Plexiform Neurofibromas
Plexiform neurofibromas are neurofibromas that arise from large nerve roots
and interdigitate with normal tissues. They have a ropy, "bag of
worms" feeling. Their cutaneous involvement may cause decreased
sensation, causing sores to develop under a brace or cast without the
patient's knowledge, or they may be hypersensitive. Underlying plexiform
neurofibromas are often covered by an area of hyperpigmented skin and/or hairy
patch. A plexiform neurofibroma has the potential for malignant
degeneration5.
Elephantiasis
Occasionally, large soft-tissue masses are seen in NF1. These masses have
been termed pachydermatocele or elephantiasis neuromatosa and are
characterized by a rough, raised, villous type of skin hypertrophy that
presents an unmistakable appearance.
Optic Gliomas
Although optic gliomas account for only 2% to 5% of all brain tumors in
childhood, as many as 70% of the cases are found in persons with NF1. They
occur in about 10% of children with neurofibromatosis. In many NF1 patients,
these tumors change little in size over many years, but a small percentage may
enlarge rapidly, leading to exophthalmos and visual impairment. Gliomas
involving the optic chiasm are the most likely to cause visual impairments and
precocious puberty.
Verrucous Hyperplasia
Verrucous hyperplasia is an infrequently occurring and unsightly tremendous
overgrowth of the skin, with thickening of a velvety-soft papillary quality.
Many crevices form and tend to break down easily, with some weeping occurring
in the skin folds.
Spinal Deformities
Spinal deformities have been noted to occur in NF1 but not NF2. The
deformities include nondystrophic and dystrophic changes. The dystrophic
changes may be intrinsic or associated with anomalies of the spinal canal
secondary to abnormalities of the spinal-cord dura mater.
The relative incidence of spinal deformities in association with NF1 is
unknown. The rate at which patients with NF1 have some disorder of the spine
varies from 2% to
36%14,15.
Of the approximately 10,000 patients with scoliosis seen by Winter et al.,
only 102 were found to fit the traditional criteria for the diagnosis of
NF116. Functional
scoliosis resulting from limb hypertrophy or long-bone dysplasia must be ruled
out in patients with NF1. All preadolescent children with NF1 should be
evaluated by scoliosis screening or the Adam forward-bend test to rule out the
presence of a spinal deformity, which usually occurs earlier in children with
NF1. The characteristic deformity tends to be a short-segmented, sharply
angulated curvature; it usually involves four to six
vertebrae17.
Recently, investigators have suggested that there is no standard pattern of
spinal deformity in NF1 and that the types of curvature are
variable18,19.
Scoliosis is the most common skeletal manifestation of neurofibromatosis.
The incidence of spinal deformities is reported to be between 10% and
60%15,20-22.
At our institution it is 23%. Spinal changes may occur throughout the course
of the disease and are usually divided into soft-tissue and osseous
abnormalities of the entire vertebral column. Some of the complications that
can occur during the treatment of spinal problems may reflect a lack of
understanding of the disease process on the part of the treating physician or
may be related to the potential pitfalls of surgery. Other complications are
inherent in the disease process itself. The goal is to prevent problems from
occurring by understanding the unusual and unique characteristics of spine
problems in NF1. It is imperative for the patient to understand the importance
of careful follow-up observation to identify signs of progression of
neurospinal disease as there is a very real, lifelong tendency for such
progression to occur.
Cervical Spine
The cervical spine in patients with NF1 has not received much attention in
the
literature23,24.
Cervical abnormalities are more likely to be overlooked when scoliosis or
kyphoscoliosis is present in the thoracolumbar region, which distracts the
examiner's attention to the more obvious deformity. Often the cervical lesion
is asymptomatic. When the lesion is symptomatic, pain is the most common
presenting
symptom25.
The most common abnormality is a severe cervical kyphosis
(Figs. 1-A through 1-D), which
is most often seen following surgery and is highly suggestive of the
disorder17. Ogilvie
reported on the surgical treatment of cervical kyphosis by anterior fusion
with iliac-crest or fibular bone graft or
both25. He
considered halo traction to be a useful preoperative step if the kyphosis was
greater than 45°. When progressive cervical kyphosis is the presenting
deformity, preoperative halo traction of flexible deformities, followed by
posterior fusion, is the treatment of choice. If the deformity is rigid, then
soft-tissue release followed by traction is believed to be safer. If
sufficient bone stock is present, internal fixation with rods, wires, screws,
or hooks may be used. Sublaminar wire fixation may be difficult secondary to
dural ectasia and osseous fragility. If there is osteolysis with poor bone
stock of the vertebral body, combined anterior and posterior fusion is
needed25 and
postoperative immobilization with use of a halo vest is recommended. Yong-Hing
et al. reported on fifty-six patients with NF1, of whom seventeen patients
(30%) were found to have cervical
abnormalities24. Of
these, seven patients were asymptomatic (the rest had either limited motion or
pain in the neck) and four patients had neurologic deficits, which probably
could be attributed to cervical instability. Four of the seventeen patients
required fusion of the cervical spine. Curtis et al. described eight patients
with paraplegia and
NF126. In four of
these patients, the paraplegia was due to cervical spine instability or
cervical intraspinal pathology.
Attention should also be paid to the C1-C2 region. Isu et al. described
three patients with NF1 who had a C1-on-C2 dislocation with a neurologic
deficit, all three of whom improved after decompression and/or
fusion27. It is
worthwhile to note that no osseous changes in the C1 to C2 relation were seen
on the flexion-extension radiographs in any of these
patients28.
Therefore, relying only on these views to detect instability is unwise. Most
of the problems that we have seen in the cervical spine were those that
occurred after excision of tumors, the operations for which included resection
of the laminae and posterior elements
(Figs. 2-A and 2-B).
Postoperatively, the spine is unstable and tends to develop progressive
kyphosis. Therefore, it is important to be aware of the patient with NF1 who
presents with a scar in and about the neck and gives a history of having a
mass removed in the past. Recently, we developed a collaborative effort with
our neurosurgery colleagues to stabilize the spinal column after removal of
tumors from the spinal canal.
Anteroposterior and lateral cervical radiographs should be made for all
patients with NF1 who (1) undergo surgery, (2) require endotracheal
anesthesia, (3) require cranial traction, or (4) present with neck tumors. If
there is any suspicion of subluxation, computed tomography or
flexion-extension magnetic resonance imaging scans are appropriate studies.
Other reasons for obtaining radiographs of the cervical spine in the patient
with NF1 include ruling out the presence of torticollis or
dysphagia29.
Because we have seen patients with erosive defects in the skull, it is
important to obtain skull radiographs prior to applying halo or Gardner-Wells
tong traction pins. Stabilization of these patients has been improved by the
addition of pedicle screw anchors when laminectomy has been necessary. A
reformatted computed tomography scan is extremely helpful to evaluate the
osseous anatomy of the cervical spine.
Thoracolumbar Deformities
Nondystrophic Curves
Peculiar to NF1 is the concept of dystrophic and nondystrophic spinal
changes. Nondystrophic scoliosis is the most common spinal deformity in NF1;
the findings, treatment, and complications are similar to those of a normal
idiopathic curve with the following
exceptions19,29,30:
(1) patients with neurofibromatosis present earlier than their idiopathic
counterparts, (2) a somewhat worse prognosis can be anticipated for
progression, and (3) there is a higher pseudarthrosis rate after spinal
fusion31. These
differences may be due to a process termed modulation (see below) in which a
nondystrophic curve takes on the characteristics of a dystrophic
curve31,32.
Treatment for nondystrophic curves: If the patient's curve
measures 20° to 25° and has less than three of the dystrophic
characteristics, treatment is by observation. Bracing is used when progression
has been demonstrated or the patient is skeletally immature and presents with
a curve >25°. Deformities exceeding 40° need posterior spinal
fusion with segmental instrumentation (Fig.
3-A). Curves >55° to 60° are treated with anterior
release with bone-grafting, followed by an instrumented posterior spinal
fusion31. This is
necessary because the curve is usually more rigid than is a similar-sized
curve in idiopathic scoliosis. We recommend postoperative orthotic
immobilization, although others have managed these patients without
postoperative immobilization, with good early
results19.
Assessment of the fusion mass by tertiary imaging (e.g., bone scan, computed
tomography, magnetic resonance imaging) at six months after surgery is highly
recommended.
Dystrophic Curves
The concept of dystrophic curves is based on radiographic findings that can
be detected at three years of age (Fig.
3-B)21.
The patient may present with a true scoliosis, with a normal kyphosis, or,
frequently, with a kyphoscoliosis, with a severe kyphotic curve of
>50°.
A dystrophic curve is characterized by a short-segmented (usually involving
four, five, or six vertebrae), sharply angulated deformity, usually in the
upper part of the thoracic spine (Fig.
4). There are nine radiographic characteristics of dystrophic
spinal deformities (Table I).
These include posterior, anterior, or lateral vertebral scalloping of the
vertebral bodies, sharpening of the vertebral margins, severe rotation of the
apical vertebra, widening of the spinal canal or the intervertebral foramina,
penciling of the ribs, spindling appearance of the transverse process, or a
paravertebral
mass17,33.
Apical vertebral rotation can become so severe that it rotates out of the
support axis such that the vertebrae are approximated against one another in a
complex three-dimensional pattern (Figs.
5-A and
5-B)16.
On plain radiographs, this may occasionally be interpreted as a congenital
deformity. Rib penciling is present when the width of the rib is smaller than
that of the narrowest portion of the second rib. Vertebral scalloping is
present when the depth of scalloping is >3 mm in the thoracic spine or
>4 mm in the lumbar spine. Although scalloping is found in all planes,
posterior scalloping is most consistent with the diagnosis of NF1. Scalloping
may also be seen in patients with Marfan syndrome. The causes of these changes
can sometimes be attributed to intraspinal pathologic processes, such as
tumors, meningoceles, or dural ectasia; however, the changes may also occur in
the presence of entirely normal intraspinal contents and with no localized
abutment from the soft tissues. These dystrophic changes are attributed to
primary bone dysplasia. Although all of these various features have been
associated with dystrophic deformity, a universally accepted diagnostic
criterion does not exist. It is important to identify patients with a
dystrophic curve because these types of curves are characterized by a rapid
course of progression and a higher rate of pseudarthrosis following
fusion.
A spinal deformity that has been diagnosed as idiopathic may show
dystrophic changes at subsequent follow-up
(Figs. 6-A and
6-B)18,31.
This condition is called modulation, a term that refers to the ability of a
spinal deformity to transform by acquiring various dystrophic morphologic
features. A nondystrophic curve can become dystrophic and a dystrophic curve
can acquire further dystrophic changes. This condition is unique to spinal
deformities in patients with NF1. These dystrophic changes may evolve slowly
or aggressively. Progressively increasing dystrophic changes in a spinal
deformity can, at a certain point, alter the behavior of the spinal curve and
herald a course of rapid curve progression
(Figs. 7-A and 7-B).
With the large number of characteristics found in dystrophic curves, it
would be beneficial to the patient and clinician to determine if one or more
of these findings may be more predictive of curves that are at greatest risk
for progression. Funasaki et al., in 1994, found that the risk factors that
were associated with substantial progression were early age of onset, a high
Cobb angle at the first examination, an abnormal kyphosis, vertebral
scalloping, severe rotation at the apex of the curve, location of the apex of
the curve in the middle to caudal thoracic area, penciling of one rib or more
on the concave side or on both sides of the curve, and penciling of four ribs
or more21. In a
recent study of ninety-one patients, the following observations were made: (1)
Spinal deformity that develops before seven years of age should be followed
closely so that any evolving dystrophic features (modulation) can be
identified. (2) When a curve acquires either three penciled ribs or a
combination of three dystrophic features, clinical progression is almost a
certainty18.
Treatment for dystrophic curves: There is no justification to
observe the dystrophic curve in NF1 because it always
progresses2,30.
Studies have shown that curves treated with a Milwaukee brace progress at a
rate similar to those that are left untreated. Early fusion is the best
treatment. Fusion in the young individual stunts the growth of the truncal
height only minimally because the curve is usually short and poor growth
potential remains in the involved vertebrae. The use of subcutaneous growing
rods, in theory, would allow for further growth, although Mineiro and
Weinstein, in 2002, questioned their value on the basis of the small amount of
growth achieved and the number of procedures
required34.
However, only one of their patients had neurofibromatosis. More recent
technological designs of universal instrumentation and localized fusion of
anchor sites of growing rods may improve these results.
Despite meticulous planning and treatment, major complications may occur
with surgical treatment even in patients without neurologic
deficit35. It is
necessary to evaluate the contents of the spinal canal to minimize the
possibility of neurologic injury during correction. High-volume myelography or
magnetic resonance imaging can be used for identifying space-occupying
lesions. Special attention should be directed toward the neural foramen to
rule out the presence of ribs protruding into the spinal
canal36,37.
We recommend that curves between 20° and 40° be fused posteriorly
with the use of instrumentation from the neutral vertebra cephalad to the
curve to the neutral vertebra caudad to the
curve29-31.
If the curve is more than 40° or the kyphosis is greater than 50°,
anterior surgery with discectomy and intervertebral fusion followed by
posterior instrumentation and fusion is
recommended29.
Winter et al. reported that, in patients with a severe curve and a flexible
kyphosis, preoperative traction improved pulmonary function, improved minor
neurologic deficits, and diminished the curve size before fusion
(Figs. 8-A through
8-D)30.
In 2002, Halmai et al. reported their protocol for treating dystrophic curves
of >60° by placing the patient in halo-vest traction for an average of
three weeks before
surgery14. They
believed that this treatment would allow the paraspinal ligaments and tissues
in the intervertebral spaces to become less tight and more hydrated, which
would assist in derotating the spine, which in turn would decrease the rate of
intraoperative neurologic complications. Careful neurologic monitoring, not
just with an evaluation of motion but also with motor strength testing, should
be documented during periods of traction. We recommend anterior release,
nasojejunal tube alimentation, and craniofemoral traction for rigid curves of
>90°. For curves >100° in any plane, anterior and posterior
release is followed by nasojejunal tube alimentation and craniofemoral
traction.
When posterior exposure is performed, careful decortication must be
undertaken because erosion of the laminae is frequently seen due to dural
ectasia. We dissect with electrocautery because of the potential of plunging
an elevator through a weakened
lamina38. Dural
ectasia, which can be identified by an increase in the width of the thecal sac
due to an increase in hydrostatic pressure, is a process that causes
expansion, erosion, and ligamentous instability to the spinal canal and the
costovertebral complex. Meticulous fusion after decortication must be carried
out with use of abundant bone graft over a broad area. Care should be taken to
remove all soft tissue from interposition in the area of the bone
graft30,39,
and all of the facet joints should be taken down. The use of autologous bone
graft is preferred to the use of bone from the bone bank. Instrumentation
should be used when possible, but dystrophic vertebrae are not always good
recipients for hooks because of osteoporosis and deformity of the posterior
elements2,40.
Hook dislocation is therefore not infrequent. Pedicle screw anchors may
provide the best foundation. In situ fusion and immobilization in a brace or
cast is rarely necessary and represents a poor alternative. The use of
biologics such as bone morphogenic protein or platelet-derived growth factor,
when approved, may benefit these patients.
If kyphoscoliosis is present (kyphosis of >50°), anterior and
posterior fusion should always be
performed29-31,41.
When anterior fusion is performed, thorough intervertebral disc-space exposure
is extremely important. The fusion must be as long as possible, with the
addition of strut-grafting. One should attempt to get the bone graft into the
vertical weight-bearing axis of the
torso30. The
recipient area should be well exposed (which is technically difficult because
of the severe apical rotation), and the strut graft that is inserted should be
in contact with bone because graft material surrounded by neurofibromatous
soft tissue has a tendency to resorb. Multiple strut grafts should be used,
and the fibula, being the strongest, should be placed most anteriorly. A rib
graft swung on a vascular pedicle may also be
helpful16. The
exposure is extremely difficult from the concave side, however, and often the
apical vertebra may be subluxated or so severely rotated that it is not in
alignment with the rest of the
spine42. Such
malalignment makes it difficult to place the anterior strut graft in the
concavity of the kyphosis. Shufflebarger believes that the anterior procedure
should be undertaken from the concave side with multiple strut grafts and that
a convex discectomy would destabilize the
spine19. We agree
completely, but we have not had a problem with the convex approach and
continue to recommend it.
Since we began to perform anterior and posterior releases followed by
craniofemoral traction for no less than ten days, the difficulty of obtaining
correction has diminished. Because of the ability to gain more correction with
extensive release and traction, we are more aggressive with the use of
anterior intervertebral segmental fusion (than with the use of strong
structural grafts), especially when it is reinforced with posterior
fusion.
Even with rigid instrumentation, postoperative immobilization in patients
with NF1 is always recommended in an effort to prevent
pseudarthrosis30.
The external support should be maintained until a fusion mass with trabecular
pattern is seen. Despite well-done surgery, pseudarthrosis with loss of
correction is not infrequent, even in the hands of experienced spine surgeons.
The reason for failure of the surgery is usually an inadequate anterior
procedure. Crawford reported a 15% incidence of pseudarthrosis in forty-six
patients29, and
Sirois and Drennan reported a 31%
incidence43. Winter
et al. reported on eight patients who underwent a planned two-stage anterior
and posterior
fusion30. Of these,
five patients healed, one patient died of respiratory complications and
paraplegia, and two patients developed a pseudarthrosis. The integrity of the
fusion mass can be evaluated with use of bone scan, computed tomography,
magnetic resonance imaging, or second-look surgery about six months after the
initial surgery. Sirois and Drennan recommended planned six-month
reexploration and augmentation procedures in patients with an isolated
posterior
fusion43.
Another complication during surgery may be bleeding. Soft-tissue
manifestations of NF1 may complicate an otherwise well-planned
surgery44.
Excessive plexiform venous channels have been described around the vertebral
bodies, making it difficult to access the
vertebrae43.
Soft-tissue tumors from NF1 may be highly vascular; thus, postoperative
hematoma is not uncommon and postoperative extradural hematoma causing
paraplegia has been
described30,43.
Therefore, meticulous hemostasis must be carried out during surgery and
Hemovac drainage must be performed postoperatively.
Sirois and Drennan reported complications that required additional surgery
in nine of twenty-three patients (39%) who underwent treatment of dystrophic
curves43. These
included four reexplorations and augmentations six months postoperatively, two
revisions for instrumentation dislocation, two extensions of the fusion mass
for curve extension, and one multiple spinal osteotomy for increasing
deformity despite the presence of a solid fusion mass. In patients who are
still growing, if anterior and posterior fusion is not done, there is an
increased incidence of progression of the curve and the occurrence of the
crankshaft phenomenon. Additional reported and not infrequent complications
include urinary tract infection, dural leak, and thrombophlebitis. After
anterior surgery, pulmonary problems with pneumonia, atelectasis, and
hemothorax may be seen. Ileus is observed, especially during the period of
time between staged anterior and posterior surgery, if the patient is kept in
traction. We strongly recommend nasojejunal tube placement and
hyperalimentation for all patients who undergo staged anterior-posterior
surgery.
Kyphoscoliosis
Kyphoscoliosis is defined as a curve with 50° or more of kyphosis. If
kyphosis is present, appropriate dynamic radiographs (i.e., a hyperextension
cross-table lateral view, made with the patient lying over a bolster) should
be performed to evaluate the flexibility of the curve. Paraplegia is not
uncommon in patients with severe kyphosis. If a flexible kyphosis is causing
paraplegia, the treatment should be craniofemoral traction (but with extreme
caution), with close neurologic or evoked potential monitoring during the
course of the
traction29,45.
A magnetic resonance imaging scan is mandatory for all patients with
paraplegia to rule out rib protrusion into the spinal
canal36,37,46.
For patients with severe deformities, three-dimensional computed tomography
scanning can be assistive in surgical planning.
If the kyphosis is flexible, the traction will correct some of the kyphosis
and also reduce spinal cord compression and possibly improve the neurologic
deficit (Figs. 9-A through
9-E)35.
Following traction, anterior release and spinal cord decompression (if needed)
and fusion should be performed, followed by a posterior fusion. Because of the
potential increase in bleeding that may occur once the patient is
normotensive, deep Hemovac drainage is necessary for all patients who undergo
anterior reconstructive surgery. Postoperatively, these patients should be
observed carefully for the development of pseudarthrosis. Augmentation of the
fusion mass should be performed at six months postoperatively if
pseudarthrosis is suspected because of loss of correction.
If the kyphosis is rigid, traction should not be
used45. Traction in
these patients stretches the mobile spinal segments that are located cephalad
and caudad to the kyphosis, increasing the tension and point compression on
the spinal cord at the midportion of the apex, which may cause further damage.
Therefore, direct anterior release, disc excision, and intervertebral fusion
followed by seven to ten days of traction, followed by posterior spine fusion,
are recommended.
The vertebral bodies are occasionally extremely porotic and will tend to
bleed freely from their cancellous surfaces. The end plate is the strongest
portion and should be protected with a meticulous anular and discal release.
The disc space should be packed with bone. Sufficient bone graft needs to be
available.
Because of the association between paraplegia and kyphoscoliosis, there is
a tendency to perform laminectomies to relieve pressure on the spinal cord.
Laminectomy only for spinal cord compression and kyphoscoliosis is
contraindicated,
however29,45.
Occasionally, a neurologic improvement may be seen after a posterior
decompression of the dura, which may temporarily release pressure on the
spinal cord. However, laminectomy does not truly decompress the spinal cord
because the compression arises anteriorly and removal of bone posteriorly
destabilizes the spine, potentially increasing the kyphosis. Furthermore,
laminectomy alone also removes valuable bone stock that will be required for a
posterior spinal fusion. Occasionally, paraplegia is related to protrusion of
a rib into the spinal
canal37. This will
usually be evident on a computed tomography or magnetic resonance imaging
scan. Removal of this protrusion should prevent progression of neuropathy.
When a rib protrusion is noted prior to surgery, osteotomy with a 2.5 to 5-cm
resection is recommended at the time of posterior fusion.
In conclusion, dystrophic thinning of the posterior elements and the
possible presence of dural ectasia of the spinal canal make the planning of
instrumentation to correct the deformity a challenge. We recommend the use of
a titanium universal rod system with hooks, wires, and pedicle screw anchors
as needed. We have on occasion used bone morphogenetic protein (off-label) to
supplement the fusion, but we have no data to support an increase in fusion
rate.
Spondylolisthesis
Spondylolisthesis in patients with NF1 is
rare47-50.
Spondylolisthesis is usually secondary to increased anteroposterior diameter
of the spinal canal, with elongation and thinning of the pedicles, causing a
pathologic forward progression of the anterior elements of the spinal column.
The causes of pathologic instability are frequently dural ectasia,
meningocele, and neurofibroma. Magnetic resonance imaging or computed
tomography and/or contrast scans are absolutely necessary for preoperative
evaluation. The treatment in severe spondylolisthesis is anterior and
posterior spinal fusion. Fusion is difficult to obtain because of the
mechanical alignment of the lumbosacral region and poor bone formation. We
recommend at least an L4-to-sacrum anterior and posterior fusion with
lumbosacral instrumentation. Postoperative immobilization is strongly
recommended.
Paraplegia
Paraplegia is not an infrequent complication of spine deformities in
NF126. The
neurologic compromise may be related to spinal deformity, instability of the
costovertebral complex causing direct protrusion of a rib into the spinal
cord, vertebral angulation, tumor, or dural ectasia. Paraplegia presenting in
skeletally immature children is frequently caused by spinal deformity, and, in
skeletally mature children, by tumor. Paraplegia that occurs after corrective
surgery is often due to the compression exerted on the spinal cord by tumors
occupying the intraspinal space. Rarely reported is the patient who presents
with paraparesis due to rib displacement. This type of paralysis may have an
insidious onset or may occur after
trauma36. Rib
osteotomy should be carried out before instrumented correction in these
patients, lest the correction cause the rib to impale the spinal cord. Osseous
dysplasia, intervertebral foraminal enlargement, and rotation of vertebral
bodies all may contribute mechanically to allow the heads of the ribs to
displace in the canal. In patients with spinal deformity, it seems that
kyphosis is the most frequent cause of paraplegia. Increased kyphosis leads to
excessive axial tension on the spinal cord and especially on the posterior
dura, which compresses the spinal cord against the anterior vertebral body.
Paraplegia is rare in a pure scoliotic curve; if present, a workup for
intraspinal pathology should be done. If paraplegia is present, magnetic
resonance imaging or a computed tomographic myelogram is appropriate to find
the cause of paraplegia. With a severe deformity, interpretation of these
images can be confusing, however, and often inconclusive.
Radicular symptoms have been reported, as well, due to vertebral
arteriovenous
fistulas44. The
most common form is a dural arteriovenous fistula that is situated in the
sleeve of the thoracolumbar nerve root. Kahara et al. recently reported a
posttraumatic arteriovenous fistula that caused radicular symptoms due to a
mass effect of the dilated epidural venous
space44.
Prior to surgery, the source of paraparesis, paraplegia, or radiculopathy
needs to be thoroughly investigated so that the surgeon is prepared to perform
the necessary surgery and have the appropriate assistance available.
Pseudarthrosis
Pseudarthrosis occurs more commonly following an attempt at spinal fusion
in patients with dystrophic or nondystrophic curves than it does in patients
with idiopathic scoliosis. The incidence is higher in patients who have a
kyphosis of >50°. Prior to the use of universal spinal instrumentation
and anteriorposterior combined surgery, reexploration and rebulking was
routinely used for patients with neurofibromatous spinal deformities. The best
results are obtained by planning a double (anterior and posterior) arthrodesis
right from the start. Even the increased strength of current instrumentation
is insufficient to obtain stability at the time of surgery when dealing with
some of these deformed, dystrophic elements.
Spinal Canal Pathology
Dural Ectasia and Intrathoracic Meningocele
A unique finding in NF1 and Marfan syndrome is dural ectasia. This is an
expansion of the dural sac from an unknown
etiology51.
Magnetic resonance imaging or high-volume computed tomographic myelography may
distinguish dural ectasia from tumor
(Figs. 10-A and 10-B). The
expanding dura may cause erosion of the vertebral body and later,
destabilization of the spine, with possible spontaneous dislocation
(Fig.
11)52-55.
Dural ectasia may in some cases expand the spinal canal so much that the
spinal cord is not injured, even if spine dislocation has occurred.
A meningocele is a protrusion of the spinal meninges through the
intervertebral foramen or through an erosion of the vertebral
body55-61.
It contains a subarachnoidal space filled with cerebrospinal fluid and causes
a paravertebral cystic swelling. It is usually located in the thoracic spine.
Meningocele and dural ectasia are a variation of the same phenomenon, with
meningocele being more localized. Meningocele may often be an incidental
finding on chest radiographs or may be associated with symptoms such as pain
or neurologic compromise. If an intrathoracic meningocele expands, causing
pressure on adjacent structures, it may cause coughing or
dyspnea61. A
massive, symptomatic meningocele should be approached surgically with removal
of the meningocele or with placement of a shunt. Consultation with a
neurosurgery colleague is highly recommended.
Dumbbell-Shaped Lesions
A dumbbell-shaped lesion is a solitary neurofibroma that is constricted as
it exits the neural foramen. The constriction gives the neurofibroma the
appearance of a dumbbell that is used by weight lifters
(Figs. 12-A and 12-B). With
continued growth, erosion and widening of the intervertebral foramen occur.
Erosion, however, may also be caused by a meningocele, and magnetic resonance
imaging may be helpful to distinguish the two entities. Neurofibromas that
arise from the spinal canal may be intradural or extradural and are most
commonly seen at the cervical and thoracic
level62. We
recommend early fusion in patients who had a laminectomy for resection of a
spinal canal tumor to prevent instability (usually kyphosis) of the spinal
column. Other tumors may come from the nerve sheath or from the nerve itself,
presenting as interstitial hypertrophy, in which case the nerve is the tumor
and the tumor is the nerve. The neurofibroma is usually benign but may cause
complications by its local growth. The intraspinal portion of the tumor may
cause spinal-cord compression and nerve root failure. The peripheral tumor may
compress blood vessels, nerves, lung, and
pleura62. Resection
of the tumor originating from the nerve may result in a neurologic loss.
Patients need to be advised of this possible neurologic deficit prior to
surgery.
While correction of idiopathic scoliosis is the goal of the spinal surgeon,
halting the progression of the deformity even with only a small correction can
be considered a good result in patients with NF1 spinal deformities. We
currently use three modalities to assess spinal cord function: transcranial
(motor and sensory evoked potential monitoring), electromyography following
insertion of the pedicle screw, and, if necessary, the gold-standard wake-up
test.
The surgeon's responsibility is to stabilize the spine in the most
expedient, safe, and permanent method possible without causing permanent
neurologic injury. ?