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|NI FEATURE: THE EDITORIAL DEBATE I-- PROS AND CONS
|Year : 2018 | Volume
| Issue : 4 | Page : 943-946
Congenital craniovertebral junction anomalies: The issues
Vijendra K Jain
Department of Neurosurgery, Max Superspeciality Hospitals, New Delhi, India
|Date of Web Publication||18-Jul-2018|
Dr. Vijendra K Jain
Department of Neurosurgery, Max Superspeciality Hospital, 1, Press Enclave Road, Saket, New Delhi - 110 017
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Jain VK. Congenital craniovertebral junction anomalies: The issues. Neurol India 2018;66:943-6
There are three main issues in dealing with congenital craniovertebral junction (CVJ) anomalies, namely, Arnold Chiari malformation (ACM), basilar invagination (BI), and atlanto-axial dislocation (AAD).
These may occur in isolation or in any combination, i.e., AAD + BI + ACM, AAD + BI, AAD + ACM, ACM + BI.,
| » Arnold Chiari Malformation|| |
The basic pathology of ACM, accepted worldwide, is that of small posterior fossa volume. Therefore, foramen magnum decompression is a well-accepted surgical procedure for treating ACM.
If ACM was due to instability at C1-C2 joints then it should have been common in patients who have demonstrable instability. In fact, ACM with demonstrable instability is rarely seen. On the other hand, C1 C2 instability is much more common than ACM. I would agree with the article by Joaquim et al., appearing in this issue of Neurology India that routine atlantoaxial fixation without posterior fossa decompression for patients with tonsillar herniation, with or without syringomyelia, and no evident CVJ instability, may not be recommended until further evidences are available. However, it is mandatory for every patient with ACM visible on magnetic resonance imaging to get a simultaneous dynamic (in flexion and extension) lateral imaging of the CVJ. In case, instability at the atlanto-axial joint is detected, then the patient should mandatorily undergo a posterior stabilization.
| » Basilar Invagination|| |
The term 'basilar invagination' was coined before the advent of the computed tomographic (CT) scan and magnetic resonance imaging (MRI), after assessing various craniometric lines and angles on plain radiographs or poly-tomograms. All these craniometric lines showed the relationship of the cranium with the axis (C2 body as well as the odontoid process) and the relationship between C1 and C2 was forgotten. The relationship of C1 and C2 could not be studied well in all dimensions on plain radiographs or on polytomography. Therefore, the high position of odontoid due to clival or occipital condylar hypoplasia or due to AAD could not be seen. Nowadays, with the advent of high quality CT scans, we can observe the anatomy of atlas (C1) and axis (C2) and their relationship very clearly in all the dimensions of space.
Therefore, it can be clearly seen that the so- called BI is only due to clival hypoplasia or it is due to the abnormal relationship of C1 and C2, i.e., C2 invaginating into the C1 ring (which may be called axial invagination/vertical dislocation/central dislocation). The clival hypoplasia by itself does not require any treatment. The axial invagination is dislocation at the atlanto-axial joints and should, therefore, be reduced, stabilized and fused.
| » Use of Spacer in Joints|| |
The use of intra-articular spacers described by Goel has revolutionized the surgical treatment of BI. However, I have some reservation in using spacers in the joints for treating BI. The most important question that emerges is whether or not by using spacers, we treat the primary pathology which causes BI? When we distract the joints and put a spacer of variable vertical height in the joint, we are primarily increasing the joint space in a vertical dimension to gain height to bring the odontoid tip downwards. The primary pathology, however, is not the decrease in vertical dimension of the joint space. In many of these patients, the odontoid tip comes down but the dislocation still persists. The primary pathology in BI due to axial invagination/vertical dislocation/central dislocation is sagittal translation and flexion at C1 C2 joints leading to an upward migration of odontoid into C1 ring, It should, therefore, be reduced by reversing this abnormal relationship between C1 and C2 in all the dimensions. This point is illustrated using a case example:
Case 1: Reduction of BI with fixed AAD
A twenty-four year old girl presented with neck pain and progressive quadriparesis. She had fixed AAD with BI. There was obliquity of both AA joints. Reduction of dislocation was performed by opening the joints posteriorly and pushing the C2 forward and downward to reverse the dislocation. Then, trans-articular screw fusion was done. Bone graft was placed on the posterior elements of the C1 and C2 vertebrae by making an artificial arch of atlas, with fusion performed using sublaminar wiring [Figure 1], [Figure 2], [Figure 3]. The BI reduced completely without the requirement of placing the spacer in the C1-2 joint space and without increasing the joint space.
|Figure 1: (a and b) Flexion and extension lateral radiographs of cervical spine showing fixed AAD|
Click here to view
|Figure 2: (a-c) Preoperative right parasagittal (right), mid-sagittal (centre) and left parasagittal (left) section of the CVJ on the CT scan through the atlantoaxial joint, showing BI with atlanto-axial dislocation along with asymmetrical C1-2 joints|
Click here to view
|Figure 3: (a-c) Postoperative right parasagittal (right), mid-sagittal (centre) and left parasagittal (left) section of the CVJ on the CT scan through the atlantoaxial joint showing the reduced BI with AAD|
Click here to view
Moreover, in an intact joint, the cartilaginous facet surfaces are smooth and one should be able to glide these surfaces over each other to reverse the dislocation. For this, one needs to have a good hold of these two vertebrae so as to be able to distract, rotate, and translate them in any angle or plane. The smoothness of the joint surfaces and the gliding capability of these articular surfaces would decrease significantly when a spacer is placed in the joint after roughening the facet surfaces and forcibly distracting the space.
| » Aad|| |
The AA joint is the most mobile joint. The dislocation can occur in all the dimensions and to various degrees.
There is agreement on what constitutes the reducible/mobile/hypermobile AAD and its treatment. Most of the discussion or controversy is about the treatment of fixed AAD/irreducible AAD. A high quality CT scan should be able to demonstrate abnormal displacement (three- dimensional) in all planes and angles., Then, one should be able to reverse the abnormal displacements and get normal alignment to finally stabilize and fuse the vertebrae in a reduced position (a simple example is that of case 1).
Surgeons often observe that fixed AAD associated with BI is present by looking at plain radiographic and magnetic resonance imaging, and also state that there is anterior and/or posterior compression at the CVJ/foramen magnum. These surgeons would plan a transoral decompression and/or posterior foramen magnum decompression with occipitocervical fusion. All these inferences and decisions are based on observing the position of the odontoid on lateral view radiographs and mid-sagittal sections of a CT scan or an MRI. However, we should study both the right and the left atlantoaxial joints as well as the three-dimensional relationship of the atlanto-axial joints for a better planning of surgery. We should find out the direction of the abnormal displacements in the sagittal, coronal and axial planes and in various angles. The difficult cases usually have dislocation in multiple directions. Transoral decompression or posterior decompression of foramen magnum with C1 arch is not the treatment of the primary problem but is the treatment of the effect of the primary problem. If we are able to reverse the abnormal displacements and thus reduce the dislocation/BI correctly, we will be treating the primary problem. All congenital AAD/BI should, therefore, be considered reducible unless one is not able to plan the reversal of the abnormal displacements with the available CT Scans.
The distraction, compression, extension and reduction (DCER) technique and its modifications by Chandra et al., and the technique described by Salunke  aim at reducing the dislocation in all the planes and angles. These novel techniques will be able to get a very good alignment in the majority of patients but one will not be able to achieve normal alignment in 100% of the patients. However, these techniques are demanding and require the surgeon to deal with the venous plexuses, the vertebral artery and the C2 roots.
The C1-C2 transarticular screw fusion [Figure 2] and [Figure 3] may be the safer instrumentation procedure as compared to the C1 and C2 screw placement, wherever it is possible. The problem of bleeding from the venous plexus is less, the C2 root manipulation is not required, and the chances of vertebral artery injury are less. Arterial injury is less likely because amongst all vertebral artery anomalies, it is rare to find the vertebral artery going through the trajectory of the transarticular screw, that is, the pars of C2, the C1-C2 joint space or the C1 lateral mass.
Finally, it is not possible to club all the cases into one group and generalize the surgical strategy. Each case should be analyzed on its own merit and the surgeon's experience. If a surgeon is confident that he can reduce and fuse the dislocation by a posterior approach alone in a given patient, he should do it. If one is not confident of reducing the dislocation from a posterior aspect or is not able to do it, then a transoral approach should be done to decompress and/or reduce the dislocation, which can be followed by a posterior fusion procedure. Some surgeons have attached some sort of stigma to the transoral surgery. It is not as difficult or as complicated as projected, and it has withstood the test of the time. We have routinely done transoral decompression with posterior fusion with excellent results over many years. Transoral surgery appears easier and simpler to me as compared to posterior C1-C2 surgery. In transoral surgery, the trajectory is straight, there is no venous plexus or vertebral artery in the trajectory, and for decompression, all that is required is drilling of the C2 vertebra. This drilling should not be a problem for neurosurgeons who routinely perform fine drilling at various sites, such as that of the anterior clinoid process, the internal auditory canal, etc. The transoral surgery went into disrepute because some surgeons did not select their cases properly. Transoral surgery was done for cases with reducible AAD, and some times, it was done for a very high BI, which was basically hypoplasia of the clivus. In such situations, the surgeons had complications.
At the end, I would like to draw attention to a new technology that will make the life of a neurosurgeon easier. The main problem that the surgeon faces in complicated CVJ anomaly is the interpretation of the CT scan to understand the exact three-dimensional anatomical relationship of C1 and C2. A study of the sagittal, coronal and axial images of the CT scan films provided by the radiology department is not always sufficient to make a mental picture of the three-dimensional anatomy in a given patient. If there is some rotation at the atlanto-axial joint, the sagittal and coronal section will not show the real relationship between the facets of these vertebrae. Therefore, the surgeon himself should study the three-dimensional reconstruction images by rotating them in all directions. Even after studying the CT scan in all these details, it is up to the individual surgeon to imagine the three-dimensional anatomy and plan his surgery. It is not easy to do this and this problem may be resolved when we start using three-dimensional printing technology. This technology provides a practical and anatomically accurate means of reproducing the patient-specific and disease-specific models of the area under consideration. These models facilitate the surgical planning, training, and simulation for the assessment and treatment of the problem. Utilization of this technology for complicated CVJ anomalies will serve surgeons, trainees, and naturally, therefore, patients.
| » References|| |
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[Figure 1], [Figure 2], [Figure 3]