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Spinal cord swelling preceding syrinx development
Case report
ELAD I. LEVY, M.D., JOHN D. HEISS, M.D., MICHAEL S. KENT, M.D.,
CHARLES J. RIEDEL, M.D., AND EDWARD H. OLDFIELD, M.D.
Department of Neurological Surgery, University of Pittsburgh, Presbyterian University Hospital,
Pittsburgh, Pennsylvania; Surgical Neurology Branch, National Institutes of Health, Bethesda,
Maryland; Department of Neurological Surgery, Cornell University; and Department of Neurological
Surgery, The Neurologic Institute of New York and Columbia University, New York, New York
U The pathophysiology of syrinx development is controversial. The authors report on a patient with progressive cervical myelopathy and a Chiari I malformation in whom spinal cord swelling preceded, by a few months, the development of a syrinx in the same location. The patient underwent a craniocervical decompressive procedure and duraplasty, and complete resolution of cord swelling and syringomyelia was achieved. This report is consistent with the theory
that patients with Chiari I malformation have increased transmural flow of cerebrospinal fluid, which causes spinal
cord swelling that later coalesces into a syrinx. The pathophysiology of syrinx development from spinal cord edema
and the success of surgical decompressive treatments that do not invade the central nervous system support the prompt
treatment of patients with spinal cord edema who are at risk for the development of a syrinx.
KEY WORDS • syringomyelia • Chiari malformation
N several different theories there is an attempt to
explain the pathophysiology of syringomyelia associated with the Chiari I malformation. In some of them,
mechanisms in which the syrinx expands progressively
from an initially small locus of syringomyelia, a “drop”
of fluid, to a cavity that is large enough to distend the spinal cord are proposed. This is the mechanism proposed for
the theories advocated by Gardner and Angel,4,5 and
Williams18–20 in which the persistence of a communication
between the fourth ventricle and the central canal at the
obex is required, as it is in the suggestion of Milhorat and
colleagues13–15 that the syrinx results from an obstruction of
the central canal by ependymal hyperplasia occluding rostral flow of CSF in the central canal. If these theories are
correct, hydromyelia arises from expansion of the central
canal, either from forces acting from above or below. On
the other hand, proponents of other theories suggest that the
pathogenesis of syringomyelia is determined by a mechanism external to the spinal cord and that the fluid comprising the syrinx is CSF that has passed through the surface of
the spinal cord along many microscopic paths, enlarging
the syrinx from without, not from within. Thus, the theories
of Ball and Dayan1 and Oldfield, et al.,16 argue that episodic elevations of either spinal venous pressure or pulse pres-
I
Abbreviations used in this paper: CSF = cerebrospinal fluid;
MR = magnetic resonance.
J. Neurosurg: Spine / Volume 92 / January, 2000
sure in the subarachnoid space, respectively, propel the
CSF through the Virchow–Robin spaces and the extracellular space of the spinal cord and into the syrinx. These
latter theories, unlike the former, imply that spinal cord
swelling and edema potentially predate the development of
a syrinx cavity. However, this stage in the development of
a syrinx has not been previously noted in a patient with a
Chiari I malformation and syringomyelia.
We present a patient with a Chiari I malformation in
whom serial MR images obtained over a 3-month period
document swelling and edema of the spinal cord that preceded development of a well-defined syrinx. Spinal cord
edema in this case is consistent with transmural passage
of CSF from the spinal subarachnoid space into the spinal
cord.1,16 The notion that spinal cord edema develops into a
syrinx is not explained by theories of syrinx pathogenesis
in which it is postulated that syrinx fluid originates from
the fourth ventricle via the central canal of the spinal cord4,5,
18–20
or results from obstruction of CSF passage within the
central canal.13–15 Because treatment with craniocervical decompression and duraplasty in this case, which opened the
CSF pathways at the foramen magnum, produced resolution of the spinal cord edema and syringomyelia, the CSF
block at the foramen magnum is implicated as the cause of
the spinal cord edema. The theory that the cerebellar tonsils
act as a piston on a partially enclosed cervical subarachnoid
space, creating enlarged cervical subarachnoid pressure
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waves that drive CSF into the spinal cord, is consistent with
the association of spinal cord edema and the Chiari I malformation in this case.16
Case Report
History and Examination. This 48-year-old woman presented with a 10-month history of progressive numbness,
paresthesias, and upper-extremity pain. Symptoms were
initially noted in her left hand and progressed gradually to
involve the other hand, the shoulders, and the arms. Clumsy hand movements eventually slowed her work on the
computer keyboard and prevented her from working. She
experienced intermittent headaches unrelated to position,
coughing, or sneezing. Treatment with corticosteroid and
nonsteroidal antiinflammatory medications was ineffective. Neurological examination revealed weakness (4/5)
and atrophy of the intrinsic muscles of both hands. Reduced sensation for pinprick and light touch were also
demonstrated in the hands. Clonus of the left ankle and
bilateral Hoffmann’s and Babinski’s signs were elicited.
Preoperative Imaging Studies. Distorted cerebellar tonsils
were seen to extend 12 mm below the foramen magnum on
the initial sagittal T1-weighted MR images of the cervical
spine. In addition, a low signal area consistent with a small
syrinx was present within the center of the cervical segments of the spinal cord extending from C-2 to C-7. Caudal
to this small cervical syrinx, the upper thoracic portion of
the spinal cord was enlarged diffusely and a homogeneous
reduction in signal intensity was demonstrated (Fig. 1 upper
left and right), an appearance consistent with spinal cord
swelling caused by edema. No enhancement was seen following gadolinium administration. The presence of a syrinx
from C-2 to C-7 and edema in the thoracic segments of the
spinal cord was confirmed on T2-weighted MR images of
the cervical spine (Fig. 1 lower left and right). The patient’s
symptoms progressed. Another MR study was performed 3
months after the initial imaging session. On this study the
diffuse signal of intermediate intensity that was noted previously in the upper thoracic portion of the spinal cord was
replaced by a syrinx with typical low signal intensity surrounded by a rim of spinal cord of normal signal (Fig. 2).
Operation and Postoperative Course. The patient underwent a suboccipital craniectomy, laminectomy of C-1, and
duraplasty. The arachnoid was translucent, and the absence
of subarachnoid scarring was visible through the arachnoid.
Thus, the arachnoid was left intact. No attempt was made
to drain the syrinx cavity. The patient made an uneventful
recovery and was discharged from the hospital with improved upper extremity pain. Follow-up evaluations at 3
and 16 months postsurgery demonstrated modest improvement in sensation and motor function.
Postoperative Imaging Studies. The syrinx resolved completely by 3 months. There was no evidence of syrinx or spinal cord edema on MR images of the cervical spine obtained
3 and 16 months after surgery (Fig. 3). The cerebellar tonsils had ascended to a normal position, and the cisterna magnum was evident dorsal to the cerebellar tonsils.
Discussion
In this report we describe a patient who developed spinal
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cord edema as an intermediate stage in the development of
a syrinx. Decompression of the craniocervical junction resulted in expansion of the CSF pathways at the foramen
magnum and the cerebellar tonsils assumed a normal morphology and position. The syrinx resolved completely, and
clinical progression was arrested.
In the respective theories of Gardner and Angel4,5 and
Williams,18–20 it is proposed that development and growth of
a syrinx results from progressive expansion of the central
canal, with CSF entering the syrinx via the central canal
and with the syrinx expanding progressively from the forces transmitted by the ventricular CSF pulse wave4,5 or by
craniospinal pressure differentials.18–20 Milhorat and colleagues13–15 have suggested that progressive expansion of
the syrinx results from the occlusion of the central canal
blocking the egress of CSF from the syrinx. On the other
hand, Ball and Dayan1 and Oldfield, et al.,16 have contended that syrinx development is caused by episodic elevations
of spinal venous pressure1 or pulse pressure16,17 in the subarachnoid space, respectively, increasing transmural passage of CSF from the spinal subarachnoid space to the
syrinx. In these latter theories the authors predict that cord
edema arises from distention of the extracellular space
of the spinal cord and precedes syrinx development and
growth, as was noted in our present case.
There is abundant supportive evidence that spinal cord
edema and syrinx fluid originate from the CSF within the
spinal subarachnoid space: 1) CSF containing ionic and
nonionic contrast media has been shown to pass from the
subarachnoid space to the syrinx on computerized tomography–myelography studies of patients with syringomyelia.12
2) Transmural flow of CSF from the subarachnoid space to
the syrinx has been demonstrated on radioactive tracer studies.6 3) Authors of experimental studies have shown that
subarachnoid CSF can enter the spinal cord through the
Virchow–Robin spaces, which surround the segmental vascular supply of the spinal cord and that these spaces are enlarged in patients with syringomyelia.1,8,10 Because radiological and pathological studies rarely demonstrate a patent
central canal in adult patients with syringomyelia,3,19 passage of CSF from the fourth ventricle to the syrinx cannot
be an important mechanism of syringomyelia progression in
adults. 4) Syrinx fluid in patients with the Chiari I malformation is identical in chemical composition to CSF,7 indicating that it originates from CSF and not from vasogenic or
cytotoxic spinal cord edema that would produce elevated
protein levels within the extracellular space and syrinx.
Because the craniocervical decompressive procedures and
duraplasty resolved the syringomyelia and cord edema in
our case, it appears that opening the CSF pathways at the
foramen magnum eliminated the force that drove CSF into
the spinal cord.9,16 Following surgery, the return of the cerebellar tonsils to a normal position and shape, as well as resolution of the dorsal hump of the medulla at the point of tonsillar impaction, together imply that these arose from a
posterior fossa that was too small for its contents rather than
a congenital central nervous system malformation.
Spinal cord edema has been reported to be a precursor to
neurological progression in patients in whom posttraumatic syringomyelia has developed. Three patients with progressive posttraumatic syringomyelia extending from the
level of their spinal injuries were reported to have increased
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FIG. 1. Sagittal and axial MR images of the cervical spine obtained 3 months before surgery. On T1-weighted images
(upper left) the abnormally shaped cerebellar tonsils extend to the upper margin of the arch of C-1, 12 mm below the
foramen magnum. A narrow syrinx is present within the center of the unexpanded spinal cord from C-2 to C-7 (arrow)
and the thoracic segments of the spinal cord are diffusely enlarged with reduced signal intensity (upper left and right).
On the T2-weighted images the spinal cord is swollen by edema (lower left and right) and the distinction between the
syrinx and the edematous spinal cord is clear (arrow in lower left).
signal intensity within the spinal cord parenchyma, as
demonstrated on T2-weighted images.11 Parenchymal
edema was seen at the advancing edge of the syrinx, which
is the craniad margin in cases of posttraumatic syringomyelia. Although the clinical symptoms correlated with the
ascending involvement of the spinal cord, in these cases
the progression of spinal cord edema to syringomyelia was
not documented by sequential MR imaging. A “presyrinx”
state of spinal cord edema has also been proposed in five
patients with nontraumatic obstruction of the CSF pathJ. Neurosurg: Spine / Volume 92 / January, 2000
ways, including one patient with Chiari I malformation.2
Although progression of edema to a syrinx without treatment was predicted, but not demonstrated, treatment that
relieved the obstruction to CSF flow resulted in resolution
of the spinal cord edema and arrest of neurological progression. Spinal cord edema must be transient before it
rapidly evolves into a syrinx; otherwise, it would have been
previously noted. Finally, despite the fact that the diameter
of the spinal cord returned to normal after treatment, thus
demonstrating that the spinal cord edema and syrinx did not
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FIG. 2. Sagittal T1-weighted MR image of the cervical spine
obtained 1 week before surgery, demonstrating that the cervical
syrinx has enlarged and a well-defined syrinx has developed in the
thoracic region of the spinal cord at the site of previously documented spinal cord edema. Note that the septum (arrow) separates
the syrinx into cervical and thoracic compartments and that the tonsillar impaction is now down to the midportion of the dorsal arch
of C-1.
produce a major loss of spinal cord substance, neurological recovery in our patient was incomplete. Consideration
should be given to early treatment if spinal cord edema is
present in a patient with a Chiari I malformation, because
subsequent syrinx formation is likely and neurological
deficits are more likely to be permanent in the presence of
a syrinx. Because decompressive surgery at the foramen
magnum, which frees the pulsatile flow of subarachnoid
CSF across this level, eliminates the pathophysiological
mechanism of syringomyelia in these patients but does not
invade the neural tissue, surgical treatment at an earlier
stage can be justified.
Conclusions
In previously reported cases of Chiari I malformation
spinal cord edema had not been documented to precede
syrinx formation. Our case supports the theory that the
pathophysiology of syringomyelia in adult patients with the
Chiari I malformation requires CSF to pass through the
spinal cord from the subarachnoid space to the syrinx. The
development of syringomyelia in an area of spinal cord
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FIG. 3. Sagittal T1-weighted MR image of the cervical spine
obtained 16 months after surgery revealing resolution of the syrinx,
the ascension of the cerebellum to a normal position above the
foramen magnum, normal shaped tonsils, and a visible cisterna
magnum. Also note the disappearance of the focal dorsal protuberance (“hump”) at the junction of the medulla and cervical spinal
cord, a morphological composition consistent with impaction of
the tonsils into the foramen magnum and brainstem distortion, that
was previously evident in Figs. 1 and 2.
edema supports early intervention in such patients by performing craniocervical decompression and duraplasty to
prevent irreversible spinal cord injury due to progression of
syringomyelia.
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Manuscript received March 22, 1999.
Accepted in final form August 16, 1999.
Address reprint requests to: John D. Heiss, M.D., Surgical
Neurology Branch, National Institutes of Health, 10 Center Drive,
10-5D37, MSC-1414, Bethesda, Maryland 20892-1414.
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