CLINICAL PICTURE

A 30 years old female patient presented clinical with gradual progressive atrophy of the small muscles of the both hands, Bilateral C5,C6 segmental hypoalgesia.

RADIOLOGICAL FINDINGS  

Figure 1. A case of congenital syringomyelia, MRI T1 images showing a longitudinal multisegmental continuous syringomyelic cavity involving the whole of the cervical spinal cord and extending to the upper dorsal segments with complete absence of transverse band and septations (Type I syringomyelic cavity). Notice herniation of the cerebellar tonsils below the level of the foramen magnum. The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

CASE OF THE WEEK

PROFESSOR YASSER METWALLY

CLINICAL PICTURE

RADIOLOGICAL FINDINGS

Figure 2. A case of congenital syringomyelia, MRI T1, T2 images showing a longitudinal multisegmental continuous syringomyelic cavity involving the whole of the cervical spinal cord and extending to the upper dorsal segments with complete absence of transverse band and septations.(Type I syringomyelic cavity). Notice herniation of the cerebellar tonsils below the level of the foramen magnum. The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

Figure 3. A case of congenital syringomyelia, MRI T1,T2 images showing a longitudinal multisegmental continuous syringomyelic cavity involving the whole of the cervical spinal cord and extending to the upper dorsal segments with complete absence of transverse band and septations (Type I syringomyelic cavity). Notice herniation of the cerebellar tonsils below the level of the foramen magnum causing marked stenosis at that level. The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

Figure 4. MRI T1,T2 images showing a central syringomyelic cavity representing dilatation of the central canal of the spinal cord, notice the peripheral signal void area (A) that probably represent a CSF flow void sign inside the syringomyelic cavity. The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

The case represents a congenital subtype syringomyelia because of the following: [19]

Table 1 Differences between congenital and neoplastic syringomyelia [19]

The presence of Arnold Chiari malformation which represents the aetiopathogenic factor of congenital syringomyelia

The central location of the syringomyelic cavity which represents dilation of the central canal of the spinal cord.

The syringomyelic cavity is a continuous slit without transverse bands or septations.

The involvement of the cervico-dorsal region of the spinal cord which is commonly the site of involvement in congenital syringomyelia.

The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

Congenital syringomyelia Neoplastic syringomyelia The presence of Arnold Chiari malformation which represents the aetiopathogenic factor of congenital syringomyelia

Absence of Arnold Chiari malformation

The syringomyelic cavity is centrally located and represents dilation of the central canal of the spinal cord (hydromyelia).

Two types of cavities are noted.

1- A peripheral irregular cavities inside the tumors which represents cystic breakdown of tumor tissue (the cavitations are part of the tumor).

2- Cavitations rostral and caudal to the spinal tumors, these cavitations are not part of the tumors and represents intramedullary cavitations due to CSF flow obstruction.

It commonly involves the cervico-dorsal region Any part of the spinal cord can be involved. The syringomyelic cavity is a continuous slit without transverse bands or septations. Transverse bands and septations are common.

The intracavitary MRI signal of the syringomyelic slit is identical with that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

The intracavitary MRI signal of the syringomyelic slit is different from that of the CSF signal in the subarachnoid spaces in MRI T1 and T2 images.

DIAGNOSIS: CONGENITAL SYRINGOMYELIA WITH TYPE I ARNOLD CHIARI MALFORMATION

DISCUSSION

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.

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. [19]

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. [19]

THE CRANIOCERVICAL ANOMALIES [19]

The following craniocervical anomalies are found in congenital syringomyelia:

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.

DIAGNOSIS:

DISCUSSION

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

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 7. A, CT myelography, B, MRI T1 image showing Arnold Chiari malformation (A,B), basilar invagination (A) and syringobulbic slit (B)

Figure 5. Chiari I malformation

Figure 6. 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 .

Figure 8. 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.

 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 9. 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

Figure 10. 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)

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. [19]

Figure 11. Arnold Chiari malformation associated with hydrocephalus and syringomyelia, notice evidence of surgical intervention

Figure 12. MRI T1 images showing a lateral syringobulbic slit with definite communication with the 4TH ventricle and the cervical syringomyelic cavity.

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 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

Figure 13. CT myelography showing a median syringobulbic slit, notice the basilar invagination.

Figure 14. A postmortem specimen showing Arnold- Chiari malformation and hydrocephalus

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 15. 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 16. 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 17. High subluxated odontoid compressing the cervico-medullary zone in a case of assimilation of atlas

Figure 18. 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.

THE SYRINGOMYELIC CAVITIES

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 19. High subluxated odontoid compressing the cervico-medullary zone in a case of assimilation of atlas (left, plain x ray,and right MRI T1 image)

 

 

 

 

 Figure 20. MRI T1 image showing TYPE I syringomyelic cavit

Figure 21. 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 22. 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. [19]

Figure 23. MRI T1 images showing type II syringomyelic cavity characterized by thick walls and extensive intra-cavitary septations, transverse bands and CSF multiloculations.

Figure 24. 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 25. 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 26. 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.

Tubular cavitation of the spinal cord, producing progressive neurologic symptoms, has long attracted interest. The accumulation of cerebrospinal fluid (CSF) can lead to simple distension of the central canal of the spinal cord lined by ependymal cells (ie, hydromyelia) or it can dissect into the surrounding white matter to form a paracentral cavity, in which case none of the cavity is lined by ependyma (ie, syringomyelia). In many if not most cases, both hydro- and

SUMMARY

syringomyelia are present, leading to the term "syringohydromyelia." As the syringomyelic cavity expands, the initial hydromyelic cavity compresses, and the communication between the two may atrophy and be lost. The distinction between hydro- and syringomyelia may be difficult even after detailed histologic examination.

Syringomyelia could be congenital, and in such a case Arnold Chiari malformation should be present, or it might be secondary to intramedullary or extramedullary spinal neoplasms, spinal trauma, spinal inflammatory conditions or spondylitic myelopathy.

Addendum

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References

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