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CLINEU 00252

ClinicalNeurology undhkwasurgery, 95 (Suppl.) (1993) W-S38 0 1993 Elsevier Science Publishers B.V. AIi rights reserved ~03-8~7~3~~.~

Neuroradiological investigations in cervical root avulsion

G.J. Vielvoyea and C.F.E. Hoffmannb

Departments of %uroradiology and bNeurasurgery, University Hospital, L&den, The Netherlands

Key words: Root avulsion; ~euro~diology; MR ~~os~py

Summary

Cervical myelogmphy in combination with CT myelography is not fully reliable to demo~stmte a partial or complete cervical root awlsion. MRI scanning can demons~ate large traumatic meningoceles or additional lesions, such as intramedullary or extradural haematomas, but not a root avulsion. In experimental conditions MR microscopy enables visualization of the avulsed root separated from the spinal cord. The anterior funiculus shows transverse tracts left behind by the avulsion at the original site of the motor fibres. However, the small bore of the current high field magnets and the very long acquisition time makes this method, as yet, unsuitable for apphcation in man.

Introduction

The cause of cervical nerve root avulsion is excessive traction force exerted on the brachial plexus. The rootlets are tom from the spinal cord and take a lateral position in the root sleeve. The ventral rootlets are shorter and therefore more prone to rupture than the dorsal ones [l]. The traction injury may produce tears in the root sleeves resulting in pseudomeningo~l~.

The early literature on this subject states that the diagno- sis of root avulsion is relatively simple because it is invari- ably associated with these pseudocysts [1,2]. Later on it became obvious that pseudocysts may contain normal or partially avulsed roots and, conversely, intact sleeves may contain partially or totally avulsed nerve roots [3-51.

Cervical myelography

The optimal way to perform cervical myelo~aphy in adults is by lateral puncture at the Cl-C2 level. The contrast medium remains accumulated by the cervical lordosis obvi- ating the need for repositioning the patient. In newborn pa- tients the subarachnoid space at the level Cl-C2 is relatively small, which makes an instillation by lumbar puncture pref- erable [3].

Corrcspondene to: Dr. G.J. Vielvoye, MD, PhD, Department of Neu~md~oIo~, University Hospital Leiden, P.O. Box 9600, 2300 RC L&en, The Netherlands. Phone: (+31)-71263319.

Lateral AP and oblique projections are made including a lateral tomography of the contrast filled spinal canal. Some- times more projections are needed, as demonstrated in a patient with a C-5 total root avulsion and partial C6 (Figs. la,b,c and 2a,b,c). The oblique projection suggests a total C6 avulsion but the other projections demonstrate an avulsion of the rostra1 part of the rootlets only, the caudal filae appear- ing intact.

In case of dural tears, contrast medium will leak into the epidural space. This will produce the so-called pseudomen- ingoceles, which extend within the spinal foramen or even beyond it down to the pleural dome [6]. The differential diagnosis of these cysts includes [7]:

abno~ally long axillary pouches or cervical root cysts; lateral intrathoracic meningoceles; and dilated nerve root sleeves in association with neurofibro-

matosis.

CT myelography

Plain CT scanning is of no help for the diagnosis of root avulsion [3]. Only a traumatic pseudocyst may be depicted, but the rootlets or their remnants are not visualized.

Recent literature singles out CT myelography (CTM) as the technique of choice in the diagnosis of root avulsion [5,8]. Small dural tears, invisible on conventional myelogra- phy, are depicted with this technique. Also encasement of nerve roots in a dural tear or compression of roots by pene- trating bony fragments is visualized. Because the thickness

s37

of

es1

it i

the e filae radicularia measures less than 0.5 mm, the small-

; al Jailable slice thickness (1.5 or 2.0 mm) has to be chosen.

If CTM is performed in addition to cervical myelography

is I necessary to wait a few hours for the contrast medium

to become diluted. A too high density of the con

would disturb the depiction of the small filae.

The introduction of spiral CT scanning f

acquisition of a large number of thin slices in

:ast me

cilitate :s the

short time.

fig . 1. Cervical myelography. a: oblique view suggesting a total avulsion at the Ct i level. b: AP view demonstrating partial avulsion. The caudal Mae

are int act. c: oblique view, with a rotation of 5 degrees compared with the AP vie :w, demonstrating partial avulsion of root C6 and total avulsion of C5.

Fig. 2. CT myelcgraphy. a: slice through the rostra1 part of C

total avulsion. b: slice through the middle part of the foramr

partial avulsion (a ventral rootlet is intact). c: slice at the c

foramen. Dorsal and ventral rootlets are intact.

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Fig. 3. MRI (9.5 T) microscopy. In a transverse section of the cervical cord

of a cat the surgically avulsed ventral root can be observed. In the anterior funiculus the low signal emitting terminal clubs are found (arrows). d: dorsal

root: v: ventral root.

3D reconstruction of the scan data provides a three-dimen-

sional model of the spinal cord and the roots, which im-

proves the anatomical image of the lesion.

measurements per slice, it is possible to obtain very good

detail. In a cat with a surgically performed avulsion of a

cervical anterior root 3 days before scanning (see also Hoff-

mann et al., this issue), we were able to detect the separation of the root from the spinal cord. Moreover, the traces of the

avulsion within the anterior funiculus of the spinal cord were

visible as low signal emitting structures, at the site of the

motor pathways. These structures probably represent the ter-

minal clubs in the spinal cord (Fig. 3). These scanners are

not available for the investigation of problems in man be- cause the bore of the magnet is too small (2.2 cm) and the

number of measurements makes the investigation time long (7 h each for each direction) for clinica! application. More-

over, the biological effects of the high field strengths in- volved are still uncertain.

Acknowledgements

The authors wish to express their gratitude to Prof. Dr. J.

Galan, University of Limburg, Belgium, and to Prof. Dr. E.

Beuls, University Hospital Maastricht, for their help in pre-

paring the cat spinal cord for MRI microscopy.

References

The value of MRI in cases of root avulsion is relatively

low [5,8]. In patients with large pseudocysts, MRI is able to

visualize the abnormal CSF space. The intact or destroyed

nerve cannot be discriminated within the cyst. MRI provides

useful additional information with respect to the presence of

intramedullary or extradural haematomas. Roger et al. [9]

report an equal reliability of CI’M and MRI of 86% in their

cases. The failure of MRI to visualize rootlets is due to their

small size. Lumbar roots are thicker than cervical ones. This

is perhaps the reason why Verstraete et al. [lo] were able to

demonstrate an intact nerve root at the lumbar level within a

pseudocyst by MRI, while CTM failed to do so. In T,-

weighted images the contrast of the roots versus the CSF is

not optimal. In T,-weighted images the contrast is better but

the signal-to-noise ratio is worse, which results in a noisier

picture without filae.

MRI microscopy

Using an MRI scanner with a very high field strength of 9.5 T (Vailant), a TR of 3000 msec, a TE of 18 msec and 70

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traumatic pseudomeningocele. Am. J. Roentgenol., 120: 887.

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