In almost all the cases of spinal lesions amenable to surgery, spinal MRI currently allows a very precise diagnosis and guidelines for preoperative planning to be established without direct contact between the patient or examiner and the prospective surgeon. The main indication for spinal MRI is usually to secure a diagnosis.

Any question directed to the examiner regarding the possible level and nature of the lesion must be formulated as precisely as possible and include an exact neurological classification of the clinical findings. This is particularly helpful when no pathological finding has been noted on MRI despite unequivocal clinical symptoms. A disturbance of gait, for instance, can be caused by cervical myelopathy, lumbar spinal canal stenosis, normal pressure hydrocephalus, Parkinson’s disease, disseminated encephalitis, polyneuropathy, an intramedullary tumor or a bone metastasis to the spine, or a spinal AV fistula—only an exact analysis of the patient’s history and the clinical findings will in this case provide the examiner with the necessary data on which to focus the examination technique. It should be borne in mind that an exclusion diagnosis, in particular, can sometimes be technically very demanding.

In addition, information from the surgeon’s point of view regarding operative strategy, which may not necessarily have been offered for a routine examination, might nevertheless become important. In order to make optimal use of the imaging equipment, thoughts about preoperative planning or additional information on how the indication was reached should, if possible, be available for consideration at the initial diagnostic MRI scanning.

The following aspects are of particular interest when a pathological finding amenable to surgery is noted on MRI:

• topographic assignment,

• specific diagnostic classification.

Documentation of level and expansion of the lesion must be precise, i.e., it must be possible for the surgeon to take responsibility for counting off each vertebral segment from the spinal sections depicted on the MR image and to transfer the findings on to plain x-rays and intraoperative fluoroscopy. The neck and upper thoracic spine will therefore require depiction of the vertebral landmarks of the craniocervical junction, and inclusion of the sacrum is necessary for the lower thoracic and lumbar spine. For the mid-thoracic spinal region, it is always obligatory to provide a sagittal reference image that includes the sacrum or the craniocervical junction.

Assigning and labeling the level of individual vertebrae on the image are only helpful when done electronically by the examiner, thus converting it into a permanent document and rendering it legally binding. Otherwise the image must be repeated in order to assure the necessary reliability of the assigned level. Labels on the film may be accurate, but they do not provide any legally binding basis for the site of the operation because it will never be certain with hindsight whether the labeling was done authentically by the examiner or later—and possibly incorrectly—by some other observer. The operative strategy of the much cited minimally invasive surgery requires, in the first instance, an exact localization—a lateralized spinal meningioma, for example, already demonstrated earlier during laminectomy, which had included the adjacent segments, can only be removed microsurgically by a stability-maintaining hemilaminectomy if it is possible during surgery to locate exactly which hemi-arch is to be removed.

The choice of slice thickness and of the interval between individual sections will depend on the dimensions of the lesion in question. For example, thin slices in the region of the tumor are decisive for preoperative planning, particularly with intramedullary tumors. With spinal metastases, on the other hand, it is important that virtually the entire spine is depicted to avoid overlooking tumor formations additional to the metastasis responsible for the symptoms. In case surgical stabilization is required, portrayal of the vertebrae adjacent to the lesion will provide enough assurance that these are not affected by the tumor and can be used for supporting the instrumentation. Since, in this case, priority lies more in including contiguous regions, it is advisable to use thicker slicing. It can be helpful if the relevant images of the various scanning planes are combined on one or a few films. However, this is no substitute for the information value provided by a complete series with regard to anatomical considerations relating to preoperative planning.

With the increasing significance of neuronavigation in spinal surgery, it will presumably be wise in future, when a finding requiring surgery is noted, to electronically store image data sets for later use by the respective neuronavigation systems after consultation with the potential surgeon. Digital documentation of the image data would be ideal, allowing appropriate evaluation at any time. Paper radiographs would then probably suffice for an overview assessment in cases of more complex lesions, where they might otherwise be limited in their informative value.

In view of the number of sections in different planes and sequences, it is helpful if the relevant images are marked with self-stick dots or the like. This can save a considerable amount of time during the overview assessment.

The specific diagnostic classification of the observed findings by the examiner is considerably more relevant than with other imaging techniques. While with CT, for example, an interpretation of the images by others poses no problem as a rule, the appreciation of why a particular MR imaging sequence was selected obviously requires additional diagnostic information that is not always available to those foreign to the matter. It is therefore of utmost importance that the examiner specify the degree of differential-diagnostic certainty of a finding.

MRI is becoming increasingly important for the emergency diagnostics of acute spinal cord paralysis so that attempts should be made whenever possible to widen the availability of this diagnostic procedure, at least on a regional basis, by allowing examinations to be also performed outside regular office hours. A spinal empyema, an epidural hematoma and a central cervical cord lesion are often difficult, or even impossible, to detect with other techniques; the density of information in a case of metastatic disease of the spine can be enlarged rapidly so as to allow well-founded indications to be defined and, perhaps, even considerations regarding an overall oncological concept to be taken into account. Routine diagnostics of spinal trauma using MRI is still certainly a problem because there are only very limited possibilities of monitoring vital signs during the diagnostic work-up. Nevertheless, it should be remembered that, e.g., the diagnostics of traumatic vascular dissection of the cervical spine, a problem area which up to now has been difficult to diagnose despite its primary importance, could be considerably better addressed in the future; a similar widening of the diagnostic spectrum can also be expected for other spinal regions.

The timing of the examination in spinal diagnostics can be decisive for the further course of the disorder. It should, therefore, always be ensured that, for example, when admitting patients with incipient paralysis or disturbance of bladder function as a sign of a transverse spinal lesion, a top-priority emergency appointment for the examination is given. The urgency depends here on the severity of the symptoms so that in the presence of marked neurological deficits an immediate examination should be performed.

Where the diagnosis automatically dictates the indication for surgery, it is often extremely comforting for the patient to receive information about treatment options from the examiner first. It helps the surgeon if, when introduced, the patient is already informed about this, yet not necessarily about a specific therapeutic procedure. The patient can only reach a decision for or against possible therapeutic measures, which often include a considerable range of variations, after close discussion with the person who will actually perform the operation. Considering the multitude of factors influencing the decision to recommend a specific operative strategy, a discussion unaffected by any previous statements should, in the interests of the patient, be all the more specific. The surgeon is certainly just as grateful to the examiner for his advice in favor of surgery as for his measured restraint regarding concrete remarks on type, extent and time frame of a possible operation.

   Surgical Management of Spinal Diseases with Reference to MRI

Objectives underlying operative management can include:

• Removal of a pathological lesion (intervertebral disk prolapse, tumor, empyema, angioma, and the like).

• Stabilization of the either primarily unstable spine or the spine having become unstable after resection of the lesion.

Stabilizing surgery sometimes forms an integral part of a primary decompressive operation, e.g., in surgery for cervical disk prolapse. On the whole there is a general tendency with regard to stabilizing operations towards instrumented spondylodesis, with titanium finding increasing use as an implant system because of the imaging problems otherwise associated with MRI. Reconstructive procedures for maintaining joint function (“disk replacement”) are still undergoing clinical trials.

Cervical Intervertebral Disk Prolapse

MRI is optimal for detecting a soft-disk prolapse and anterior narrowing of the spinal canal or intervertebral foramina by marginal osteophyte formation in the form of a “hard” disk prolapse. The aim of surgery is decompression of the nerve root(s) or the spinal cord. Even if the main feature of the clinical picture is a radicular lesion or cervical myelopathy, equal attention should be paid during surgery not only to sufficient radicular but also medullary decompression.

b Preoperative state.

Fig. 2.3 Operative site during cervical fusion. The Caspar plate is seen deep down, stably fixed to the cervical spine by screws.

Fig. 2.4 Fully consolidated cervical fusion of C5/6. Here polymethylmethacrylate (PMMA) was used as a spacer, often referred to clinically as a “dowel.” Final fusion is not complete until years after surgery when the PMMA beads are covered on all sides by bone.

Fig. 2.5a—c Implantation of a Sulfix dowel:

a Finding after implantation of a Sulfix dowel as a replacement for the removed disk C5/6.

b Note the typical signaling on the T1-weighted image.

c The changes on the T2-weighted image are typical for long-term reactions in the adjacent vertebrae, which can demonstrate marrow edema and fatty marrow formation and cause local symptoms.

Fig. 2.6a—e Formation of artifacts after implantation of titanium spacers in the intervertebral cavity during surgery for stenosis of the cervical spinal canal secondary to osteochondrotic ridging at the C5/6/7 level:

The extent of the artifact effect depends on the sequences selected and, particularly in the axial sequences, can have considerable influence (b, c) or hardly any at all (d, e).

  Operative technique of anterior operations on the cervical spine