Radiological pathology of congenital syringomyelia

INDEX
 INTRODUCTION,
PATHOGENESIS,
PATHOLOGY
 THE CRANIOCERVICAL
ANOMALIES
o ARNOLD-CHIARI
MALFORMATION
o SYRINGOBULBIA
o BASILAR
INVAGINATION
o ASSIMILATION OF
ATLAS
 THE SYRINGOMYELIC
CAVITIES
CONGENITAL SYRINGOMYELIA
Syringomyelia is a chronic disorder involving the spinal cord or the medulla or both.
Pathologically it is characterized by the development of cavitations and gliosis within these
structures. When cavitations and gliosis extend to the medulla (bulb), the term
syringobulbia is applicable.
www.yassermetwally.com
Professor Yasser Metwally

The present term "syringomyelia" was devised by ollivier in 1837 from the two Greek
words "to become hollow" and "marrow". This term was intended to describe any
cavitation in the spinal cord including even the central canal which had not been
recognized as a normally occurring structure until stifling described it in 1859.
In order to understand the pathogenesis of congenital syringomyelia it is necessary to
understand the dynamics of the CSF flow in the central canal of the spinal cord and the
surrounding subarachnoid spaces.
The bulk flow of the CSF follows a downward route behind the spinal cord and posterior to
the dentate ligament from the cervical region and down to the lumber region and then
upward in front of the spinal cord to the basilar cisterns. Pressure waves are generated by
the distension and the collapse of the cerebrovascular and the spinovascular beds and are
felt to be responsible for the CSF pulsation. As in case of the blood, the propagation of the
pulse waves is independent of and much faster than the blood velocity. Also the
propagation of the CSF pulse wave is much more rapid than the actual CSF movement.
The CSF down flow, which occur behind the spinal cord, begins during systole and ceases
during diastole and is of 10 times greater volumetric magnitude than the ventricular pulse.
The ventricular CSF pulse wave is generated by the pulsation of the choroid plexus in the
lateral ventricles which then escapes through the foramen of magendi into the
subarachnoid spaces and is progressively damped as it passes down behind the spinal cord
through the foramen magnum; in this way the central canal of the spinal cord is bypassed
and is not subjected to the ventricular fluid pulse wave and is left behind as a potentially
distensible vestigial structure.
Around 30% of the CSF is formed in the central canal of the spinal cord and flow upward
by the milking action of the CSF pressure waves that are transmitted to the walls of the
spinal cord. These pressure waves are thought to be caused by engorgement of the spinal
venous plexus and are most marked during coughing, straining and other valsalvas effect
producing maneuver.
THE CRANIOCERVICAL ANOMALIES1
The following craniocervical anomalies are found in congenital syringomyelia:
Arnold-Chiari
malformation
(100%) Cerebellar tonsillar ectopia
Basilar invagination (25%) Complete intracranial invagination of the atlas
and axis
Syringobulbia (15%) Medullary cavitation
Hydrocephalus (10%) mmm
Klippel feil anomaly (5%) Complete fusion of bodies and arches of

adjacent vertebrae
Assimilation of the atlas (5%) Atlanto-occipital fusion
 Arnold-Chiari malformation
Stenosis of the foramen magnum, due to cerebellar tonsillar ectopia, with the resultant of
reduction of the volume of the foramen of magendi, as it opens anatomically between the
two cerebellar tonsils, will disrupt the normal CSF circulations and pulse waves. This will
interfere with the escape of the ventricular pulse waves and pressure waves generated by
the choroid plexus situated at the obex of the 4th ventricle (this escape normally occurs
through the foramen of magendi and the foramen magnum) and direct them into the
central canal of the spinal cord, resulting in syrinx formation.
Figure 1. Chiari I
malformation
Figure 2. The anatomic
substrate of congenital
syringomyelia and/or
hydromyelia is based upon
cerebellar tonsillar ectopia
in fetal life. Blockade of
the foramen of magendi
and stenosis of the
foramen magnum will
funnel the CSF arterial
pulse waves into the spinal
canal, distending it and
eventually creating
hydrosyringomyelia .
Stenosis of the foramen magnum and the foramen of magendi can also inhibit the CSF
upflow from the central canal of the spinal cord towards its intracranial sites of resorption

and causes increased spinal CSF pressure. The CSF, driven by the high intraspinal
pressure, will thin filter into the spinal cord resulting in longstanding cord oedema that
eventually causes cavitations within the spinal cord parenchyma.
Figure 3. A, CT myelography, B, MRI T1 image showing Arnold Chiari malformation
(A,B), basilar invagination (A) and syringobulbic slit (B)

Figure 4. MRI T1 images (A,B) showing Arnorld-Chiari malformation.

Interestingly the foramen of magendi (which is situated at the
caudal end of the 4th ventricle and can easily be appreciated on
the T1 MRI sagittal images) is appreciated as being markedly
diminished in volume and occasionally totally obliterated and
unidentifiable in all patients with tonsillar ectopia. In some
patient the foramen of magendi is transformed into a long slit
that opened below the level of the foramen magnum.
Figure 5. MRI T1 image showing a case with Arnold-Chiari
malformation, notice the tonsillar ectopia, adhesions between
the herniated tonsils and the medulla, resulting in marked
stenosis of the foramen magnum and the foramen of magendi
Adhesion between the herniated cerebellar tonsils and the posterior aspect of the cervico-
medullary junction could be appreciated in all cases, so besides stenosis of the foramen
magnum and the foramen of magendi that is induced mechanically by the crowding of the
foramen magnum by the herniated cerebellar tonsils, these adhesions will further
compromise the volume of the foramen of magendi.

Figure 6. Normal MRI T1 image (left) and two cases with Arnold Chiari malformation
(middle and right images), notice the tonsillar ectopia,adhesions between the herniated
tonsils and the medulla, resulting in marked stenosis of the foramen magnum and the
foramen of magendi,also notice the syringobulbic slit (right image)
Figure 7. Arnold Chiari malformation
associated with hydrocephalus and
syringomyelia, notice evidence of surgical
intervention
 Syringobulbia
Syringobulbic slits are demonstrated in 15% of cases with syringomyelia and they are
composed of two types, the first type extends asymmetrically into the lateral tegmentum of
the medulla, in the presumed area of the descending root of the trigeminal nerve. The other
type extends along the median raphe. Direct communication between the bulbic slits and
the 4th ventricle is occasionally demonstrated in some cases.

Figure 8. MRI T1 images showing a lateral syringobulbic slit with definite communication
with the 4TH ventricle and the cervical syringomyelic cavity.
Figure 9. CT myelography showing a
median syringobulbic slit, notice the
basilar invagination.

Direct communication between the bulbic slits and the cervical syringomyelic cavities is
commonly demonstrated in almost all cases, this is because syringobulbia is formed by
fluid in the cervical syringomyelic cavities breaking upward through the pyramidal
decussation region to form a cavity in the bulb. Pulsatile fluid shifts in the cervical syringes
are responsible for the upward extension of these syringes. all the bulbic slits are
demonstrated on both the T1 and T2 weighted MRI images, both in the axial as well as the
sagittal planes.
 Hydrocephalus
Hydrocephalus is demonstrated in about 10% of
cases with congenital syringomyelia and is
occasionally associated with an abnormally elongated
cerebellum and a markedly distorted 4th ventricle
with significant reduction of its volume. This
probably indicates the existence of a graver degree of
stenosis at the 4th ventricular level. This marked
degree of stenosis apparently results in
hydrocephalus in addition to hydrosyringomyelia.
Occasionally hydrocephalus is associated with
abnormally large cisterna magna .
Figure 10. A postmortem specimen showing Arnold-
Chiari malformation and hydrocephalus
Figure 11. A, This figure illustrates the position of the downwardly displaced portions of
cerebellum. The lower medulla has a congenital "kink." The position of the foramen
magnum, as it appeared in life, is marked on the image. B, This figure illustrates the brain
stem and cerebellum cut sagitally in a case of Arnold-Chiari malformation. The arrow
points to the cerebellar tonsils or "pegs" of cerebellum which have been displaced caudally
over the roof of the medulla.

 Basilar invagination
Complete intracranial invagination of the atlas and axis (basilar impression or
invagination) is demonstrated in about 25% of cases with congenital syringomyelia. Basilar
impression acts by reducing the volume capacity of the posterior fossa and crowds the
cerebellum thus producing cerebellar tonsillar herniation, thereby sitting up the substrate
for the funneling of the CSF pressure waves into the central canal of the spinal cord thus
creating hydrosyringomyelia. In all cases with basilar impression the odontoid process was
fixed with no evidence of subluxation.
Figure 12. Basilar invagination plain x ray (left) plain CT scan (middle) and MRI T1
image(right), notice that the hyperintense odontoid (due to increased fat content) can be
seen in touch with the pons
 Assimilation of atlas (atlanto-occipital fusion)
Assimilation of the atlas (complete fusion between
the atlas and the occipital condyles) occur in about
5% of cases of congenital syringomyelia. In atlanto-
occipital fusion, the odontoid process is abnormally
high, subluxated and compressing the cervico-
medullary junction posteriorly. The most significant
finding in assimilation of the atlas with neurological
symptoms is an odontoid process with abnormal
size, in abnormal position and with abnormal
mobility .
Figure 13. High subluxated odontoid compressing
the cervico-medullary zone in a case of assimilation
of atlas

Figure 14. High subluxated odontoid compressing the cervico-medullary zone in a case of
assimilation of atlas (left plain x ray and right two images CT myelography)
When the atlas is fused with the occiput, flexion of the head results in partial forward
subluxation of the fused atlas on the axis. Posterior displacement of the odontoid process
then occurs, resulting in compression of the cervico-medullary junction. As the posterior
luxation of the odontoid process is intermittent (only during head flexion), so intermittent
compression of the cervico-medullary junction might result, initially, in intermittent
neurological manifestations.
Regarding the cervico-dorsal syringomyelic cavities, two types are demonstrated. The first
one was composed of a single, continuous slit-like or tubular cavity that extended through
the whole cervico-dorsal region. The walls of these cavitations are thin and smooth. Signal
loss on the T2 weighted images (CSF flow void sign) is occasionally demonstrated inside
these cavitations. Patients harboring this type of cavitations are younger.
Figure 15. High subluxated odontoid
compressing the cervico-medullary
zone in a case of assimilation of atlas
(left, plain x ray,and right MRI T1
image)

THE SYRINGOMYELIC CAVITIES
Figure 16. MRI T1 image showing TYPE I syringomyelic cavity
Regarding the cervico-dorsal syringomyelic cavities, two types are demonstrated. The first
one was composed of a single, continuous slit-like or tubular cavity that extended through
the whole cervico-dorsal region. The walls of these cavitations are thin and smooth. Signal
loss on the T2 weighted images (CSF flow void sign) is occasionally demonstrated inside
these cavitations. Patients harboring this type of cavitations are younger.

Figure 17. MRI T1 images showing TYPE I syringomyelic cavity composed of a single,
continuous slit-like or tubular cavity that extended through the whole cervico-dorsal
region. The walls of these cavitations are thin and smooth.

Figure 18. MRI T2 image (A) and CT myelography (B) showing TYPE I syringomyelic
cavity composed of a single, continuous slit-like or tubular cavity that extended through the
whole cervico-dorsal region. The walls of these cavitations are thin and smooth. Signal loss
on the T2 weighted image (CSF flow void sign) is evident on the T2 image
On the other hand, the second type is characterized by thick walls and extensive intra-
cavitary septations, transverse bands and CSF multiloculations. The CSF flow void sign is
not demonstrated inside these cavitations on the T 2 weighted images. Patients harboring
this type of cavitations are older.

Figure 19. MRI T1 images showing type II syringomyelic cavity characterized by thick
walls and extensive intra-cavitary septations, transverse bands and CSF multiloculations.

Figure 20. MRI T1 images (A) and MRI T2 image (B) showing type II syringomyelic cavity
characterized by thick walls and extensive intra-cavitary septations, transverse bands and
CSF multiloculations. The CSF flow void sign can not be demonstrated inside these
cavitations on the T 2 weighted image.
From the pathological point of view syringomyelia is a chronic spinal cord disorder
characterized by progressive cavitations and gliosis. Cavitations occur early and progress
up and down by the pulsatile fluid shifts inside the syringomyelic cavities. Pulsatile fluid
shifts inside the cavitations are caused by CSF pulsation in the subarachnoid spaces that is
transmitted to the fluids inside the syringomyelic cavities through the walls of the spinal
cord. These pulsatile fluid shifts are increased by coughing and straining and result in
recurrent sucking and sloshing of the CSF inside the syringomyelic cavities.

Figure 21. Type II syringomyelic cavities, notice the thick walls, and traverses septations
Such sucking and sloshing movements of the CSF inside the cavitations result, on short
term basis, in progressive extension of the cavitations up and down within the substance of
the spinal cord. The pulsatile fluid shifts in the syrinx cavities are thought to be responsible
for the loss of signal on the T2 weighted images that has been termed CSF flow void sign
(CFVS). However on long term basis pulsatile fluid shifts in the syringomyelic cavities
induce reactive gliosis that ultimately results in the formation glial bands, septations and
CSF multiloculations inside the syringomyelic cavities. It also results in progressive
thickening of the walls of the cavities and probably also reduction of the volume of the
cavitations.

Figure 22. Type I syringomyelic cavities.
These glial bands and septations will interfere with the CSF flow inside the cavitations by
damping the pulsatile CSF movement. This ultimately results in stasis of the CSF inside the
cavitations and loss of the CSF flow void sign that was initially present at a younger age.
Symptoms of syringomyelia are initially caused by the progressive cephalo-caudal
extension of cavitations caused by the pulsatile fluids shifts inside these cavitations. The
pulsatile fluid shifts vary in intensity from time to time and from one position to another.
Engorgement of the epidural venous plexus by prolonged recumbency and during coughing
and straining also increases the intensity of the pulsatile fluid shifts. The variability of the
intensity of the pulsatile fluid shifts is reflected clinically as marked fluctuation of the
intensity of the clinical symptomatology of some of these patients to the point that some of
them were initially misdiagnosed as MS.
At an older age group symptomatology of syringomyelia is caused mainly by the reactive
gliosis that can interfere with the blood supply of the affected segments and with the
physiological function of the myelin sheath and neurons at the affected zones, thus
resulting in progressive deterioration of the clinical neurological deficits.
In congenital syringomyelia, shunting of the syringomyelic cavitations is probably
indicated only when the CSF flow void sign could be appreciated inside these cavitations on
the T2 weighted images, especially when MRI also demonstrates absence of any significant
glial septations and/or CSF multiloculations, i.e. shunting is indicated only for type I
syringomyelic cavitations.
Early surgical treatment can relieve the distending force (i.e. sucking and sloshing CSF
movements) and perhaps - on long term basis - can prevent the gliotic zone which later
surround the syringomyelic cavities. Post-operatic absence of the CSF flow void sign that
was initially present pre-operatively is an indication of a successful shunting.

REFERENCE
1- Metwally,MYM : Imaging of syringomyelia, a comparative study. Read at the scientific
meeting of the Egyptian society of neurology, psychiatry and Neurosurgery, Port Said,
October 1993
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Radiological pathology of congenital syringomyelia

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