Comparison of CT myelography performed in the prone and supine positions in the detection of cervical spinal stenosis

AIM: To quantify the change in the cross-sectional area of the cervical spinal cord and subarachnoid space (SAS) in the supine neutral vs prone extension positions in patients with myelopathy undergoing cervical CT myelography. MATERIAL AND METHODS: Axial CT myelgrams of 21 myelopathic patients were performed in both the supine neutral and prone extension positions. The SAS and cord cross-sectional areas were then measured at the disk spaces and mid-pedicle levels from C2 to T1 in both the supine and prone positions using a public domain NIH Image program, version 156b18. Mean area measurements in both positions were then compared for each level examined. RESULTS: Mean SAS cross-sectional area in the prone position was notably reduced compared with the supine position at C4-C5 [128.8 mm2 vs 168.1 mm2 (P<.05)], and C5-C6 [98.8 mm2 vs 143.2 mm2 (P<.05)] disk levels. The mean cord cross-sectional area failed to change significantly with positioning. CONCLUSIONS: Prone myelography may demonstrate a greater degree of cervical spine stenosis compared with CT myelography performed in the supine position in myelopathic patients. Imaging with the patient prone with neck extended in both myelography and CTM may improve precision in the results of measurements of the stenotic spinal canal when comparing these two methods. Blease Graham III, C. (2001). Clinical Radiology56, 35-39.     

MRI of the cervical spine with neck extension: is it useful?

Objectives

Standard MRI of the cervical spine is performed in a different anatomical position to that utilised for traditional contrast myelography. Those well practised in myelography are familiar with the considerable changes in configuration of the bony and soft tissues of the cervical spine that may occur with changes in the degree of neck flexion and extension. We set out to compare the findings in a select group of patients with myeloradiculopathy who had undergone myelography and MRI in both standard and neck-extended positions. These findings were correlated with the clinical status.

Methods

29 patients underwent myelography with CT (CTM) and MRI in neutral and neck-extended positions. The imaging was assessed for the degree of cord compression and neural foraminal narrowing, quantified using a simple grading scheme suitable for routine clinical practice. The degree of neck extension was assessed using an angular measurement.

Results

For both CTM and MRI, scanning with the neck extended significantly increases the severity of cord compression compared with the standard supine position, to a degree similar to that shown during conventional prone myelography. The degree of perceived cord compression is related to the degree of neck extension achieved. Correlation of standard MRI findings and the clinical level of radiculopathy is poor. This correlation improves when the neck is extended.

Conclusions

The most appropriate position for routine MRI of the cervical spine in degenerative disease remains unknown, but in selected patients imaging with the neck extended may provide important additional information.With the introduction of spinal surface coil technology and gradient echo sequences in the late 1980s, MRI rapidly replaced intrathecal contrast myelography as the standard imaging method for assessment of the cervical spinal cord and nerve roots. The two investigations are performed in very different anatomical positions. Standard cervical spine MRI is performed in a coil that is designed to make the patient comfortable, to minimise movement-related artefacts. This generally results in a position of mild extension of the neck. On the other hand, the majority of images for plain cervical myelography are obtained with the patient prone and the neck hyperextended so as to retain myelographic contrast within the cervical lordosis. CT myelography (CTM) is typically performed with the patient supine and with the neck straight or mildly flexed; however, CT myelography can also be performed in the prone position with the neck extended [1].For a number of years we continued to use plain myelography, with CTM as a second-line investigation in patients with cervical myelopathy and/or radiculopathy, when the results of standard MRI were inconsistent with symptoms and signs. More recently we have also performed MRI with neck extension, predominantly in patients with myelopathic features but inconclusive supine MRI. We have been unsure how extended MRI compares with myelography and whether it is able to produce the same degree of extension as myelography. We have performed CT in the prone extended position as well, but have also been unsure how that relates to standard supine CT imaging or to extended MRI. We therefore wished to compare these various modalities in a heterogeneous group of clinically problematic patients.     

Hirayama disease: MR diagnosis.

We report the MR findings in two cases of Hirayama disease, a kind of cervical myelopathy related to flexion movements of the neck. In flexion MR studies, we can see the striking and pathognomonic picture of anterior shifting of posterior dura at the lower cervical spinal canal. In nonflexion studies, we find that asymmetric cord atrophy, especially at the lower cervical cord, though subtle, is highly suggestive of Hirayama disease. When it is seen, a flexion MR study is warranted to prove this diagnosis.     

Idiopathic spinal cord herniation

Idiopathic spinal cord herniation is a rare disease, few cases having been reported. We encountered a case of idiopathic spinal cord herniation presenting with severe spasticity in the right leg and urinary dysfunction. The spinal cord was herniated into a cavity created by duplication of the dura mater and resection of the inner layer improved the neurological deficits. MRI, myelography, and CT myelography were useful for diagnosing this disease. Four radiological signs of spinal cord herniation are described.     

Cervical chordoma presenting with intervertebral foramen enlargement mimicking neurofibroma: CT findings

A cervical chordoma, confirmed at surgery, presented on plain spine films as a focal enlargement of the intervertebral foramen and mimicked the characteristic appearance of cervical neurofibroma. Computed tomography (CT) of the cervical spine was obtained immediately following metrizamide myelography; it demonstrated a soft-tissue mass in the enlarged intervertebral foramen that extended posteriorly to compress the spinal cord and anteriorly to compress the hypopharynx. The mass was sharply demarcated, inhomogeneous, and low in attenuation; CT density measured between those of cerebrospinal fluid and muscle. Although this CT appearance is not specific for cervical chordoma, it is unusual for neurofibroma. Cervical chordoma should be considered in the differential diagnosis of focal enlargement of cervical intervertebral foramina.     

Cervical myelography: survey of modes of practice and major complications

A total of 68 major complications of cervical myelography were reported by 220 neuroradiologists in a mail survey. Two-thirds of the complications were attributed to cervical spine hyperextension and one-third to lateral C1-2 puncture. Narrow sagittal diameter of the spinal canal and severe cervical spondylosis were frequent contributing factors to hyperextension injury of the cervical spinal cord. Clinical and radiographic premyelography screening is suggested, with magnetic resonance imaging performed first in patients with spinal canal stenosis, severe spondylosis, and/or myelopathy of any cause. Neck extension should be minimal during myelography. All C1-2 punctures should be monitored with lateral fluoroscopy for accurate needle positioning and prevention of contrast medium injection into the spinal cord.     

An unusual spinal intradural arachnoid cyst

Spinal intradural arachnoid cysts are seen most frequently in the thoracic region, particularly near the midline posteriorly. A thoracic intradural arachnoid cyst in this typical location is reported, with the additional unusual finding of herniation of the spinal cord through an anterior defect in the dura mater. The MRI findings are described.     

Functional cervical myelography with iohexol

Summary Thirty patients underwent functional cervical myelography, i.e. radiographs in the lateral view were obtained in extension as well as in flexion of the neck. Sagittal tomography was performed in both positions. Widening of the subarachnoid space and decreased sagittal diameter of the spinal cord due to shortening were demonstrated in the lateral view in flexion. In some cases with advanced narrowing or spinal block in extension, such widening in flexion resulted in better diagnostic images by providing passage of the contrast medium caudally. Although iohexol (Omnipaque, Nyegaard & Co., Oslo) was regularly forced into the posterior cranial fossa by the movements, the frequency of side effects was approximately the same as in our former trials with iohexol in conventional cervical myelography. EEG changes occurred in two patients (7%). A sitting position for 3–4 min after the examination followed by an elevated head end of the bed was probably important for preventing side effects from the contrast medium. Specific questioning revealed twice as many subjective side effects as reported after general questions alone.     

Comparison of myelography, CT myelography and magnetic resonance imaging in cervical spondylosis and disk herniation. Pre- and postoperative findings

Twenty-six patients with cervical radiculopathy and/or myelopathy caused by spondylosis or disk herniation were examined with myelography, CT myelography and MR. Fourteen of the patients were operated upon and 11 of them underwent postoperative MR and CT. The three radiologic methods provided comparable information about narrowing of the subarachnoid space and compression of the spinal cord. It was more difficult to distinguish bone from soft tissue with MR only, but the combination of MR and conventional radiography gave sufficient information for this differentiation. When radiologic nerve root sheath deformity was compared with clinical radiculopathy, myelography, CT myelography and MR had similar sensitivity and accuracy. Postoperative MR could reveal remaining indentation on the thecal sac and the cord but CT without contrast medium was useful as a complement to determine the aetiology of the indentation. Because MR has several practical advantages, it is well suited as the primary imaging modality, together with conventional radiography, for the preoperative radiologic evaluation of patients with cervical radiculopathy and/or myelopathy. Postoperative MR is useful in patients with persistent or new symptoms.     

Classification system based on kinematic MR imaging in cervical spondylitic myelopathy.

BACKGROUND AND PURPOSEFunctional myelographic studies are often used to evaluate the dynamic changes of the cervical spinal canal during flexion and extension. The purposes of this study were to use kinematic MR imaging to assess the dynamic changes of the cervical spine in patients at different stages of degenerative disease and to describe a classification system based on static and dynamic factors in the pathogenesis of cervical spondylitic myelopathy.METHODSEighty-one patients with different stages (I-IV) of degenerative disease of the cervical spine were examined with MR imaging. In the neutral position (0 degrees) and at maximum flexion and extension, spinal stenosis was classified for each segment according to the following grading system: 0 = normal, 1 = partial obliteration of the anterior or posterior subarachnoid space, 2 = complete obliteration of the anterior or posterior subarachnoid space, and 3 = cervical cord compression or displacement.RESULTSAt flexion and extension, the prevalence of spinal stenosis and cervical cord impingement increased as the stage of degenerative disease progressed. With regard to a pincer effect (anterior and posterior cord impingement) and cord encroachment at multiple segments, statistically significant differences were observed at stages III and IV as compared with stages I and II. Significant increase in cord impingement was seen in 22 (27%) of 81 patients at extension, as compared with four (5%) of 81 patients at flexion.CONCLUSIONRegardless of the stage of degenerative disease and grade of spinal stenosis at the neutral position (0 degrees), cervical spinal motion may contribute to the development of cervical spondylitic myelopathy.     

Metrizamide CT myelography in cervical myelopathy and radiculopathy: correlation with conventional myelography and surgical findings

Conventional myelography, metrizamide computed tomographic (CT) myelography, and surgical findings were correlated in 30 patients with cervical radiculopathy and/or myelopathy. In 60% of patients, metrizamide CT myelography provided significant additional information including better characterization of the abnormality, lateralization if the conventional myelogram was indeterminate, more definitive demonstration of cord atrophy, foraminal narrowing not appreciated on myelography, and demonstration of abnormalities distal to a myelographic block. In no case was a myelographic abnormality not detected on metrizamide CT myelography. In patients with cervical myelopathy, a cross-sectional diameter of the cord equaling less than 50% of the subarachnoid space is predictive of poor patient response to surgical intervention.     

Morphology and dimensions of the thoracic cord by computer-assisted metrizamide myelography

Computed tomographic (CT) measurements of the thoracic spine and its contents were obtained in 33 patients undergoing metrizamide myelography for various spinal disorders. Twenty-eight of these patients had symptoms referable to the cervical or lumbar region and form the basis of this study. Five patients had symptoms referable to the thoracic spine. Sagittal and coronal CT measurements of the thoracic cord and subarachnoid space were obtained in all cases. In addition, macroscopic measurements of the thoracic cord were obtained from 10 autopsies for correlation with the CT findings. The technical aspects of the measurements are discussed; the normal morphology of the thoracic cord and thecal sac is presented; and the metrizamide CT pattern associated with pathologic lesions involving the thoracic cord is analyzed.     

Comparison of MR and CT myelography in imaging the cervical and thoracic spine

MR imaging and CT myelography were compared in a retrospective study of 38 patients with suspected lesions of the cervical and thoracic spinal canal and cord. Twenty-eight abnormal cases were found, including spondylosis (9), tumors (8), intramedullary cavities (3), arachnoiditis (3), disk-space-centered infection or osteomyelitis (2), nonneoplastic cord swelling (2), and CSF-borne metastasis (1). MR was equal or superior to CT myelography in depicting cases of cord enlargement, cord compression, and cord atrophy, providing better tissue characterization, no shoulder artifact, and no limitation caused by CSF block. CT myelography was superior to MR in depicting cases of spondylosis and arachnoiditis. It showed superior spatial resolution, which was most pronounced when comparing axial images and hence particularly superior in detecting the lateral extent of disk herniation. Use of surface coils and thin imaging sections is essential for accurate and complete MR evaluation of the cervical and thoracic spine.     

Lateral C1-2 puncture for cervical myelography. Part III: Historical, anatomic, and technical considerations

Three significantly different lateral approaches to the cervical subarachnoid space (anterior, midplane, and posterior needle positions) have been previously described for cordotomy and myelography. Experimental lateral C1-2 punctures were performed by each of these three methods in anatomic specimens, cadaver models with reconstituted cerebrospinal fluid pressures, a patient with cerebral death, and to a limited degree in patients undergoing routine cervical myelography. In the cervical region the dura is pushed ahead of the needle, forming a "tent" over the needle tip during C1-2 puncture; the needle projects several millimeters into the spinal canal before penetrating the dura, regardless of the method of entry or needle diameter. The extent of this tenting phenomenon and its relationship to the spinal cord are significantly affected by the needle diameter and position. A posterior technique for lateral C1-2 puncture is described.     

Spinal cord herniation: report of two cases and review of the literature

Idiopathic herniation of the spinal cord is an extremely rare disorder which may cause progressive myelopathy. Two cases of this entity reported herein were both examined using MRI and CT myelography. The typical appearance of this disease with or without a dorsal intradural arachnoid cyst is focal ventral displacement of the mid-thoracic spinal cord, mimicking an isolated intradural spinal arachnoid cyst on MRI. CT myelography using thin slice sections is useful in the diagnosis of this disease. Received 14 August 1995; Revision received 30 January 1996; Accepted 4 June 1996     

Complete myelography with metrizamide

Thorough myelography of the entire spinal cord including the foramen magnum region can be accomplished consistently and promptly after metrizamide injection via lumbar or lateral cervical puncture. When lumbar puncture is used the patient's torso is oblique, but the neck is prone and straight and the table is tilted 20 degrees head-down to allow direct cervical filling with contrast material. Each region is filmed in several projections, the patient being turned gently from the prone cervical to the supine thoracic position. Of 100 cases without block studied in this way, all had adequate cervical and foramen magnum films. In only five was the contrast material too dilute to show the edges of the spinal cord well and the subarachnoid sac adequately in the thoracic region. In 29 patients, there were mild side effects not requiring medication, while 20 had side effects of a more moderate to severe nature. No seizures were encountered. Metrizamide proved a convenient, efficient, and acceptable contrast medium for myelography when a study of the entire spinal cord is indicated.     

Computed tomographic myelography in the investigation of childhood scoliosis and spinal dysraphism

The combined investigations of positive contrast myelography and computed tomographic (CT) myelography were performed on 53 consecutive children. Thirty-eight (72%) of these investigations were performed as a routine pre-operative procedure to identify occult spinal dysraphism in patients with childhood scoliosis; the remainder were because of the "orthopaedic syndrome", cervical radiculopathy, back pain and patients with clinical findings to suggest spinal dysraphism. In the 20 patients (38%) with idiopathic scoliosis, there was no case of spinal dysraphism and CT myelography provided no additional information to the myelogram. In the seven patients with spinal dysraphism the plain radiographic abnormalities identified were lumbar vertebral abnormalities (five), thoracic vertebral abnormalities (one), and sacral agenesis (one). Diastematomyelia was found in four patients, a low tethered cord and lipoma in two patients and a large lipoma in one patient. In all of these cases the myelogram indicated the intraspinal abnormalities; however, CT myelography provided more precise anatomical detail. We conclude that CT myelography is not indicated in the initial preoperative assessment of idiopathic scoliosis but should be reserved for patients with congenital or complicated scoliosis where the association with dysraphism is well recognised.     

Cervical myelopathy: a comparison of magnetic resonance and myelography

Fifty-seven patients with a strong clinical suspicion of cervical myelopathy were studied with body coil magnetic resonance (MR) and conventional myelography or CT myelography. Eight patients were believed to have normal studies with both modalities. There were six patients with syringomyelia; four with an intramedullary tumor; one with an arteriovenous malformation; 19 with cervical spondylosis at multiple levels; eight with cervical spondylosis at a single level; four with extensive rheumatoid arthritis; four with extradural neoplasm; two with trauma; and one patient with an epidural abscess. In this study, body coil MR was the superior examination for the evaluation of an intramedullary process. It was as diagnostic as myelography in one case of an extramedullary intradural lesion. In patients with extradural disease, body coil MR was the superior study in 45%, equivalent to myelography in 37%, and, although still diagnostic, inferior to myelography in 17%. In 8% of the cases, body coil MR was at best equivocal, whereas myelography was diagnostic. It appears that in technically adequate studies, MR is at least equivalent to myelography in its ability to delineate disease. A superior MR study provides a better appraisal of the size and character of the spinal cord as well as the degree of both anterior and posterior defects on the subarachnoid space and neural structures. In addition, MR is as good as conventional myelography for the identification of extrinsic cervical cord lesions producing cervical myelopathy. Finally, an additional small group of 30 patients were studied with a prototype surface coil to determine its advantages relative to body coil imaging. Each patient had correlative myelography. As with body coil MR, imaging with the surface coil was believed to be more informative than conventional myelography in four patients with intramedullary lesions. The remaining 26 patients suffered from cervical spondylosis. Surface coil MR was believed to be more informative than myelography in six cases (23%), equivalent to myelography in 19 (73%), and less diagnostic than myelography in one (4%). The improved spatial resolution with the use of the surface coil was believed to increase the accuracy of MR.     

MR visualization and clinical significance of the anterior longitudinal epidural venous plexus in cervical extra-axial lesions

A thin band of intermediate signal intensity behind the cervical vertebral bodies, demonstrated on sagittal MR images, was attributed to the anterior longitudinal epidural venous (AEVP). Percentage visualization and clinical significance of this structure were evaluated in extra-axial lesions of the spinal cord. In review of 50 normal controls, the percentage visualization of this structure at each cervical vertebral level was 25.5% on T1 weighted sagittal SE images, while that of T2 or proton density weighted SE images was 26.0%. AEVP was demonstrated by sagittal MRI in 29 of 128 extra-axial lesions of the cervical cord (22.7%), including cervical spondylosis, ossification of the posterior longitudinal ligament (PLL), herniated disk and spondylosis at a single level. AEVP in these conditions was often thickened compared with normal controls, probably due to venous engorgement and contribution of the dura mater and PLL. Posterior displacement of this structure or "lifted band appearance" indicated herniated disk or posteriorly protruding osteophyte, demonstrating true anteroposterior diameter of the spinal canal. Demonstration of AEVP on sagittal MRI was important in the diagnosis of extra-axial lesions of the cervical cord.     

Central spinal cord lesions in stenosis of the cervical canal

Summary 34 patients suffering from cervical spondylotic myelopathy confirmed by myelography were examined by delayed CT 6–10 h after myelography. Twelve patients showed bilateral intramedullary collections of contrast medium, predominantly cranial to the stenosis. In these patients males predominated, the duration of clinical symptoms lasted longer although their age was lower. There was no correlation to the degree and the extension of the narrowing of the cervical spinal canal. Half of 20 patients undergoing consecutive decompressive surgery showed intramedullary contrast enhancement, and this was shown again by postoperative MRI in eight. The postoperative clinical and neurophysiological results revealed no change in the majority of patients, but three patients showing intramedullary contrast medium deteriorated in neurophysiological outcome, while only one of the patients in whom intramedullary contrast medium was not noticed got worse.