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Advances In Spinal Radiology

Dynamic MRI

Conventional magnetic resonance imaging (MRI) of complex cervical spine disorders may underestimate the magnitude of structural disease because imaging is performed in a nondynamic non-weight-bearing manner.

Pictured above: Dynamic MRI image showing the spine in extension
Weight-bearing magnetic resonance (MR) imaging of the spine can either be simulated by imaging the patient in the supine position in combination with a special axial loading device or be achieved by using vertically open-configuration MR systems, which allow for in vivo MR images of the spine under upright weight-bearing conditions in either seated or standing body positions. Weight-bearing MRI of the spine permits the study of physiological as well as pathological changes in the relationships of the intervertebral disc, the spinal canal, and the neural foramina as well as the assessment of segmental instability in physiologic body positions. With this technique, MR images may be taken in painful body positions so that morphological changes of the intervertebral disk or other spinal structures may be correlated with pain or other symptoms. In selected cases, weight-bearing MRI of the spine may demonstrate clinically relevant neural compromise or foraminal stenosis, which may be occult on conventional MR images obtained in the supine position.

Abnormalities more pronounced on weight bearing MRI than on recumbant MRI include fluctuating anterior and posterior disc herniations, hypermobile spinal instability, central spinal canal and spinal neural foramen stenosis and general sagittal spinal contour changes. Potential relative beneficial aspects of upright, weight-bearing dynamic-kinetic spinal imaging over that of recumbent MRI include the revelation of occult disease dependent on true axial loading, the unmasking of kinetic-dependent disease, and the ability to scan the patient in the position of clinically relevant signs and symptoms. Dynamic scanners are open and thus this imaging has low claustrophobic potential and yields relatively high-resolution images with little motion artifact.

 

Cervical discography
Cervical disc puncture with contrast dye injection under fluoroscopic guidance, is an increasingly used modality in the evaluation of patients with intractable neck pain. MRI remains the most commonly performed and useful tool in the diagnostic evaluation of symptomatic cervical discs and provides noninvasive and accurate assessment of disc anatomy and pathologic change. However, correlation of pain with abnormalities of structural anatomy is not always reliable, and cervical discography is a diagnostic procedure used in complementary fashion with other imaging techniques to yield the precise disc level responsible for pain and to aid in planning treatment.

The status of a hypointense signal (dark) cervical disc and/or a small herniated disc on magnetic resonance imaging has not been determined. Magnetic resonance imaging can identify most of the painful discs but still has relatively high false-negative and false-positive rates. There is a high chance that hypointense signal and small herniated discs are the pain generators, but they are not always symptomatic. Discography can therefore prevent unnecessarily fusion of asymptomatic levels. A combination of clinical symptoms, magnetic resonance imaging, and discography provides the most information for decision making and can improve the management of cervical discogenic pain.

The procedure is an anatomical challenge. At least 2 different techniques exist for performing this procedure. The paravertebral technique uses digital palpation to retract vital soft tissue structures such as the trachea, carotid artery and oesophagus. The oblique approach obviates the need for digital palpation. After spinal needles are placed within the centre of the nucleus pulposus, contrast is injected to determine internal disc architecture and any pain response provoked.

The improvements in contrast media, imaging technique, meticulous attention to aseptic technique combined with use of antibiotics have resulted in very low rates of complications. Complications include discitis, epidural abscess, quadriplegia, stroke, pneumothorax, nerve injury, and spinal cord injury. The rate of cervical discitis is low, reported to be around 0.37%.

 

Pet scans in myeloma
Flurorine–18 fluorodeoxyglucose positron emission tomography (FDG-PET) is able to detect bone marrow involvement in patients with multiple myeloma whose bone scan is negative and to assess its appearance and distribution pattern. It can also contribute to initial staging of multiple myeloma and might be useful for follow up of patients in remission.

It is useful in assessing extent of disease at time of initial diagnosis, resulting in more accurate staging. FDG PET is also useful for evaluating therapy response.

Therapeutic
Image guided Pedicle Screw Placement
Computerized stereotactic image-guidance has been used in recent years to improve the accuracy and safety of pedicle screw placement during spine surgery.

The integration of digital image-guided surgical navigation with C-arm fluoroscopy, known as virtual fluoroscopy (VF), has been shown to enhance the safety of spine surgery in vitro. However, few clinical studies have assessed the accuracy of VF during actual spinal surgery, and no studies have investigated variations in accuracy over the course of a series of measurements obtained during operative cases.

Fluoroscopic images of the lumbar spine are obtained, calibrated, and saved to the Stealth Station (FluoroNav). The tracking arc is attached to an exposed lumbar spinous process, which is designated the index level. With use of anatomic surface irregularities in the laminae and spinous processes, several points are identified and registered on three different vertebrae directly adjacent to the index level vertebra.

Results suggest that the use of VF is a reliable method of verifying the use of anatomic and/or radiographic landmarks for guidance during lumbar pedicle screw placement.

It has been suggested that the imaging model of the lumbar spine and the surgically exposed lumbar spine may differ significantly. The possibility of intervertebral motion exists, and because the patient is usually in a different position when preoperative imaging is performed compared with the operative position, current protocols suggest registering each spinal level (single-level registration) separately before pedicle screw placement at that level, a time-consuming process. However, early evidence suggests that single-time, multilevel registration may decrease operative time relative to repeated, single-level registrations, without compromising the increased accuracy of pedicle screw placement afforded by this technique in the setting of degenerative disorders of the lumbar spine.

Placement of pedicle screws in situations in which posterior element anatomy is altered, such as in the presence of a prior fusion mass, is challenging. The normal anatomic landmarks used to determine the starting point and trajectory of the screws have either been removed or are obscured by the fusion mass. Computerized frameless stereotaxis provides precise intraoperative real time multiplanar image-guidance and may be valuable in this clinical situation. Accuracy rate of 96% have been achieved using stereotactic image-guidance to place pedicle screws into previously fused lumbar spines.

 

Percutaneous Nucleoplasty
Nucleoplasty is performed for decompression of contained herniated discs. It is one of the least-invasive techniques in the minimally invasive category, thus far exhibiting a very low incidence of complications. It can be performed under local anaesthesia and sedation on an outpatient basis. Potential candidates for percutaneous disc decompression using coblation are those patients with back and leg pain caused by contained herniated discs.

Access to the disc is via the posterolateral discography approach, with a 17-gauge introducer needle inserted through the annulus and into the nucleus. The introducer remained in place within the outer annulus during the entire procedure, providing access for the probe into the nucleus. The device is heated up to 40-70°C, ablating the centre part of the disc and creating a channel. After stopping at a pre-determined depth, the probe is then withdrawn, coagulating the tissue as it is removed. Around six channels are created during the procedure, the number of channels depending on the desired amount of tissue reduction.

Percutaneous disc decompression using Coblation (Arthrotec UK Ltd) implements the principle of volumetric reduction to achieve disc decompression and reduce intradiscal pressure. Nucleoplasty achieves reduction in volume and intradiscal pressure with minimal damage to surrounding tissue in the treated disc.

NICE noted the lack of long term follow up make it difficult discriminating outcomes with the natural history of the underlying condition. However, although no long-term data is available, preliminary results indicate that the Nucleoplasty procedure is a safe and moderately effective procedure for reducing pain in patients presenting with predominant discogenic low back pain associated with contained disc herniation. Randomised, controlled studies with subgroup analysis are required to further delineate the role for this procedure.

 

 

Vertebroplasty and Kyphoplasty
Percutaneous vertebral augmentation or vertebroplasty is the injection of acrylic bone cement (commonly polymethylmethacrylate; PMMA) into bone cavities in order to relieve pain and/or stabilise the bone.

Pictured above: Dyaminc MRI image showing the spine in neutral position
Papers reporting the results of vertebroplasty are usually retrospective case series with small numbers. There does however seem to be evidence of reduced pain and improved function when used to treat osteoporotic fractures. An overall complication rate of between 1- 5% is reported when vertebroplasty is used to treat osteoporotic fractures. Potential risks include infection (<0.5%), pulmonary embolus, radiculopathy and paralysis (1 case in literature). More frequent complications are the risk of adjacent vertebral body fracture and cement leakage.

Nice guidelines for vertebroplasty were issued in 2003 and for kyphoplasty in 2006. There was consensus that evidence on the safety and efficacy of percutaneous vertebroplasty appears adequate but that this procedure should only be undertaken by clinicians who have received adequate training to achieve an appropriate level of expertise.

The procedure should be limited to patients whose pain is refractory to more conservative treatment.

They reported on evidence suggesting improved pain scores in patients treated with kyphoplasty when compared to control patients treated with either conventional medical treatment or vertebroplasty although uncertainty was expressed that these improvements were maintained in the long term.

Vertebral augmentation is also a potential treatment option in patients with painful, progressive osteoporotic or osteolytic compression fractures. The procedure is relatively straight forward, with a low complication rate. However, it should only be performed by physicians who have received sufficient training as there is the potential for catastrophic complications. Early results suggest that it can be effective in restoring stability and reducing pain although longer term results are less clear cut and further follow up is required.

 

 

 

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