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Year : 2017  |  Volume : 12  |  Issue : 3  |  Page : 227-231

Delineate, yet not dread: Anomalous vertebral artery in pediatric congenital atlantoaxial dislocation and basilar invagination

Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India

Date of Web Publication14-Nov-2017

Correspondence Address:
Pravin Salunke
Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jpn.JPN_64_17

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Introduction: The deformed joints seen in congenital atlantoaxial dislocation (CAAD) are often associated with vascular anomalies. It is important to identify these vascular anomalies and address them appropriately without compromising the manipulation and fusion of C1–C2 joints. The small bones in pediatric age group pose an additional challenge. Materials and Methods: Data of fifty-six children with CAAD operated in the last 4 years was analyzed. A computed tomography angiogram was obtained preoperatively to assess for the course of the third segment of vertebral artery (VA). The anomalous VA was dissected and safeguarded during drilling and manipulation of the C1–C2 joints. Results: Of the 112 VAs, 5 were aplastic, 21 crossed the joint posteriorly. Only one patient with reducible atlantoaxial dislocation (AAD) had anomalous VA crossing the joint posteriorly, the remaining VA anomalies were seen with irreducible AAD. Anomalous VA was seen on both sides in 2 patients. The most common anomaly was an inverted VA seen in seven sides. In all patients, the anomalous VA could be dissected and safeguarded without compromising the C1–C2 dissection and manipulation and fusion. In children, even the normal VA may occasionally pose difficulties while manipulation of joints. Challenges while addressing the anomalous and normal VA in pediatric age group have been described. Techniques to overcome these have been discussed. Conclusion: It is important to delineate the anomalous VA. However, the presence of such an artery is not a deterrent to the manipulation of C1–C2 joint, essential for best results. Special attention needs to be paid to the extent of distraction, medial C2 transverse foramen, and dissection/drilling of the area superior to the anomalous VA in the pediatric age group.

Keywords: Congenital atlantoaxial dislocation, injury prevention, operative steps, pediatric, vertebral artery anomaly

How to cite this article:
Salunke P. Delineate, yet not dread: Anomalous vertebral artery in pediatric congenital atlantoaxial dislocation and basilar invagination. J Pediatr Neurosci 2017;12:227-31

How to cite this URL:
Salunke P. Delineate, yet not dread: Anomalous vertebral artery in pediatric congenital atlantoaxial dislocation and basilar invagination. J Pediatr Neurosci [serial online] 2017 [cited 2020 Nov 26];12:227-31. Available from: https://www.pediatricneurosciences.com/text.asp?2017/12/3/227/218244

   Introduction Top

The congenital atlantoaxial dislocation (CAAD) is often a result of deformed C1–C2 joints. The vertebral artery (VA) in such deformed joints may take a different course than usual.[1] Such anomalous course of VA needs to be identified to avoid its injury during joint manipulation.[1] The smaller caliber of vessels and small bones pose a challenge in the pediatric age group.

The presence of anomalous VA should not take the focus away from C1 to C2 joints.[2] Fusion of occipital squama to the C2–C3 is not desirable, especially in children as the long-segment fusion may hamper the growth apart from the restricting neck movements.[3],[4],[5] Fusing the C1–C2 joints is possible despite the anomalous VA.[1],[2] This manuscript discusses the author's experience with anomalous VA encountered during the management of pediatric CAAD and how short-segment C1–C2 fusion is still possible.

   Materials and Methods Top

Fifty-six pediatric patients (<18 years of age) with CAAD were operated in the last 4 years in our institute. Preoperative three dimensional-computed tomography (CT) angiograms were obtained in all patients. The course of VA was studied from its exit from C2 transverse foramen till its entry into the foramen magnum. Special attention was paid to the C2 transverse foramina. The caliber of VA on either side was compared. The C2 nerve root ganglia were dissected from the anomalous VA and cut. The V3 segment was mobilized and safeguarded by gently retracting it away from the working corridor. The C1–C2 joints were drilled and packed with bone chips. Metallic spacers were used to compensate for the bone loss due to comprehensive drilling. The C1 lateral mass screws and C2 pedicle screws were inserted and further manipulated to achieve the multiplanar realignment. Finally, the rods were tightly fastened after some compression. Alternatively, Goel's plate was used in 32 patients in whom atlantoaxial dislocation was in anteroposterior or vertical plane and could be reduced easily with traction or just by the intraoperative joint opening. The artery was safeguarded in all steps. The VA in pediatric CAAD posed a different challenge due to smaller bony size. Special care was taken to avoid the over distraction. The dissection of VA that crossed the posterior surface of inferior C1 facet required baring of the bone superior to the anomalous VA. The C2 transverse foramen was defined, especially when it was medially located, and care was taken to protect the intraosseous portion of VA as well. The technical nuances have been described in the discussion section below.

   Results Top

Five different types of VA anomalies were encountered [Table 1]. The C2 transverse foramen was more medial than usual in six VAs. The artery then traverses across the posterior surface of isthmus and joint to enter the C1 transverse foramen laterally. Medial border of C2 transverse foramen was delineated in such cases, and the C2 pedicle screw was inserted medial to it. Inverted V3 segment was seen in seven sides. The artery traversed on the inferior surface of C1 arch making insertion of C1 lateral mass screw difficult. The persistent first intersegmental artery (FIA) was seen in four sides, and this made drilling the joint and insertion of spacers or bone chips difficult. The fenestrated artery was seen in three sides. Five VAs were atrophic. The anomalous VA could be mobilized in all. The nuances have been described below in discussion. The anomalous artery was not a deterrent in these children to achieve a good intraoperative reduction and fusion. [Figure 1] shows the bilateral anomalous VA course with nonassimilated C1 arch. The arteries were mobilized and C1–C2 joints (not OC2) were fused after reduction while safeguarding the arteries.
Table 1: Types of vertebral artery anomalies in pediatric patients with congenital atlantoaxial dislocation

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Figure 1: Upper row – preoperative images (a) Midsagittal computed tomography image showing atlantoaxial dislocation both in anteroposterior plane and vertical plane. (b) Coronal computed tomography constant velocity joints showing vertically oriented C1–C2 joints. The OC joints are normal and including occiput would hamper the movement unnecessarily. (c) Three dimensional-computed tomography angiogram as seen posteriorly showing bilateral vertebral arteries passing below the C1 arch (white arrows). (d) Parasagittal computed tomography passing through C1–C2 joint showing its oblique orientation. Lower row-postoperative images (e) Midsagittal computed tomography showing excellent reduction of C1–C2 in both planes. (f) Coronal computed tomography showing drilled joints with spacers. (g and h) axial computed tomography through C1 and C2 showing the placement of lateral mass and pedicle screws

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There was complication of injuring a VA in its normal course lateral to the joint in one of the cases. The bleeding was easily controlled with pressure. There was significant manipulation of the joint. After an uneventful recovery in the immediate postoperative period, the patient developed PICA infarct on day 3 and finally succumbed. Another patient with normal VA course developed severe brain stem edema on day 3 and died.

   Discussion Top

The cause of CAAD and so called Basilar invagination (BI) lies in the abnormal orientation of C1–C2 joints;[6],[7] these patients are born with oblique joints, both in sagittal and coronal planes. The C1 starts slipping over the C1 anteriorly and inferiorly. The rate of slip and direction of slip is decided by the degree of obliquity in sagittal and coronal plane. A joint oblique in sagittal plane leads to dislocation in anteroposterior plane, whereas a joint more oblique in coronal plane would dislocate more in vertical plane leading to central/vertical dislocation or so called BI. The dislocation is accentuated by the occipitalized arch of  Atlas More Details and C2–C3 fusion due to increased stress at C1–C2 joints. The methods to measure joint orientation have been described previously.[6]

The author comprehensively drill the joints to make them flat both in coronal and sagittal planes.[7] Further realignment can be achieved by manipulating the C1-C2 facetal screws and rods.[8] Inserting the screws as close the point where the forces act, i.e., as close to joint as possible provides the best results. Fusing the occipital squama to the C2 may be suboptimal unless the C1–C2 joints have been dealt with.[3] Fusing the joints in reduced position (irrespective of the instrumentation used) is the best option.[3] Once, they have been dealt with, inclusion of the occipital squama may be unnecessary.[4]

VA is often seen posterior to the C1 lateral mass in occipitalized arch of atlas or may pass through a bony canal. In fact, VA may course obliquely over the C1–C2 joint (persistent first intersegmental artery/FIA) or may hug on the inferior surface of the fused or free C1 arch (Inverted VA).[9],[10] Variants of VA or branches crossing the C1–C2 joint posteriorly have described in details. The presence of FIA or inverted VA is not a deterrent to dissection of joint, insertion of spacers, and its manipulation.[1],[2],[9],[10] The artery can be dissected, mobilized, and safeguarded throughout the procedure. The operative nuances for the same have been already described. Similarly, the presence of bony canal through the lateral mass is not a contraindication for insertion of the lateral mass screw. The insertion point and direction of the screw can be decided by studying the CT angiogram carefully. This study shows that in all patients with anomalous VA, good reduction, and fusion of the C1–C2 joints posteriorly could be achieved. [Figure 1] is an example showing the bilateral VA crossing the C1–C2 joint posteriorly. The dislocation did not reduce on traction, necessitating intraoperative reduction by opening the joints. The occiput-C1 joints are normal, and OC2 fusion just to avoid the anomalous VA would compromise the neck movements significantly. The VA was dissected, mobilized, and safeguarded without compromising the C1–C2 fusion with a good outcome. Even when the atlas is assimilated, fusing the squama to the C2 is not a good option, and C1–C2 fusion close to joints is feasible.[3],[4],[11]

There have been recent publications in the classification of VAs and CAAD with risk stratification.[12],[13] One of these studies observed that VAs often have an unusual course in the presence of occipitalization of arch of atlas, either passing through the bony canal or lies beneath the arch of atlas.[12] The bony canal itself may be anterior, posterior, or through the lateral mass. In the presence of normal C1, the VA was abnormal only in 15% of cases, passing below the C1 arch. The authors did not use distract the joints and avoided lateral mass screws in the presence of anomalous or unusual course of VA.[12] Another study stratifies the risk of VA in surgery for CAAD.[13] However, any classification of the course should be relevant surgically.

Special considerations in pediatric age group

Certain situations require a special consideration. The C1 lateral mass may be small in the pediatric age group. In addition, an incurving occiput may block the view to already assimilated C1 lateral mass. In such cases, the mobilization of anomalous VA, especially a dominant one with, relatively, large-caliber becomes difficult. The C1 arch just above the lateral mass or incurving occiput needs to drill. It is preferable to dissect superior to the anomalous VA and expose the lateral mass. The anomalous VA can then be gently retracted caudally to expose the lateral mass. The screw can be inserted above the anomalous VA if it is persistent FIA or below it if it is an inverted one. Goel's plate can be slid beneath the artery, and screws can be inserted into the lateral mass after retracting the anomalous VA superiorly or inferiorly depending on it course.

In cases with FIA, the space of joint lateral/medial to the artery can be utilized to drill it flat in all planes and for the insertion of spacers/bone chips. The portion of joint posteriorly available for it opening and drilling depends on the C2 transverse foramen in cases of FIA. A more medial C2 transverse foramen provides more space lateral to the FIA and vice versa. Of course, the artery needs to be mobilized along good length of course to aid its safe retraction.

In cases of fenestrated VA, the danger is yanking the segment from the parent vessel while dissecting and manipulating the joint. The segment crossing the C1–C2 joint posteriorly can be sacrificed if its caliber is thinner than the other segment in normal course.

The transverse foramen of C2 may be medial, and the intraosseous proximal VA may have a further medial course. The VA needs to be safeguarded during the drilling of medial, and superior portion of C2 isthmus that is already small in pediatric cases. The medial portion of the transverse foramen can dissect, a probe (thin dissector) can be insinuated medially into the intraosseous portion, thereby safeguarding the VA while inserting the C2 pedicle screw.

The VA is usually redundant in its V3 segment. However, the redundant length is relative to size to the joints and lateral masses. In adults, the lax segment is approximately 6–8 mm (calculated mathematically to accommodate for the normal C1–C2 rotation). It implies that the joint can easily be distracted by 5–7 mm in adults. However, in children, the length may not be as much allowing lesser distraction. The excessive distraction may stretch the VA and injure its endothelium. Such injury is likely to thrombus formation and embolization leading to brain stem infarct in a delayed fashion (2nd or 3rd postoperative day). It is preferable to give anticoagulants in patients after excessive manipulation.

It may be difficult in certain cases with pseudofacets or supernumerary facets to dissect and safeguard the VA.[14] Similarly, significant planning may be necessary for lateral translation or angular dislocation.[15],[16] However, with experience, one can easily safeguard the artery without compromising the C1–C2 joint dissection and manipulation in any plane of dislocation. The insertion of a C1–C2 prosthesis may be difficult in the presence of FIA or inverted VA.[17]

   Conclusion Top

It is important to identify the course of VA to address it appropriately intraoperatively rather than taking the approach away from the joint.

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Conflicts of interest

There are no conflicts of interest.

   References Top

Salunke P, Futane S, Sahoo SK, Ghuman MS, Khandelwal N. Operative nuances to safeguard anomalous vertebral artery without compromising the surgery for congenital atlantoaxial dislocation: Untying a tough knot between vessel and bone. J Neurosurg Spine 2014;20:5-10.  Back to cited text no. 1
Salunke P, Sahoo S, Deepak AN. Anomalous vertebral artery is not a deterrent to C1-2 joint dissection and manipulation for congenital atlantoaxial dislocation. Neurol India 2015;63:1009-12.  Back to cited text no. 2
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Salunke P, Sahoo SK, Sood S, Mukherjee KK, Gupta SK. Focusing on the delayed complications of fusing occipital squama to cervical Spine for stabilization of congenital atlantoaxial dislocation and basilar invagination. Clin Neurol Neurosurg 2016;145:19-27.  Back to cited text no. 3
Goel A. Occipitocervical fixation: Is it necessary? J Neurosurg Spine 2010;13:1-2.  Back to cited text no. 4
Tauchi R, Imagama S, Ito Z, Ando K, Hirano K, Muramoto A, et al. Complications and outcomes of posterior fusion in children with atlantoaxial instability. Eur Spine J 2012;21:1346-52.  Back to cited text no. 5
Salunke P, Sharma M, Sodhi HB, Mukherjee KK, Khandelwal NK. Congenital atlantoaxial dislocation: A dynamic process and role of facets in irreducibility. J Neurosurg Spine 2011;15:678-85.  Back to cited text no. 6
Salunke P, Sahoo SK, Deepak AN, Ghuman MS, Khandelwal NK. Comprehensive drilling of the C1-2 facets to achieve direct posterior reduction in irreducible atlantoaxial dislocation. J Neurosurg Spine 2015;23:294-302.  Back to cited text no. 7
Salunke P, Sahoo S, Khandelwal NK, Ghuman MS. Technique for direct posterior reduction in irreducible atlantoaxial dislocation: Multi-planar realignment of C1-2. Clin Neurol Neurosurg 2015;131:47-53.  Back to cited text no. 8
Salunke P, Sahoo SK, Ghuman MS. Bilateral inverted vertebral arteries (V3 segment) in a case of congenital atlantoaxial dislocation: Distinct entity or a lateral variant of persistent first intersegmental artery? Surg Neurol Int 2014;5:82.  Back to cited text no. 9
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Patra DP, Salunke PS, Sahoo SK, Ghuman MS. Redundant anomalous vertebral artery in a case of congenital irreducible atlantoaxial dislocation: Emphasizing on the differences from the first intersegemental artery and operative steps to prevent injury while performing C1-2 joint manipulation. Ann Neurosci 2015;22:245-7.  Back to cited text no. 10
Goel A, Kulkarni AG, Sharma P. Reduction of fixed atlantoaxial dislocation in 24 cases: Technical note. J Neurosurg Spine 2005;2:505-9.  Back to cited text no. 11
Sivaraju L, Mani S, Prabhu K, Daniel RT, Chacko AG. Three-dimensional computed tomography angiographic study of the vertebral artery in patients with congenital craniovertebral junction anomalies. Eur Spine J 2017;26:1028-38.  Back to cited text no. 12
Sardhara J, Behari S, Mohan BM, Jaiswal AK, Sahu RN, Srivastava A, et al. Risk stratification of vertebral artery vulnerability during surgery for congenital atlanto-axial dislocation with or without an occipitalized atlas. Neurol India 2015;63:382-91.  Back to cited text no. 13
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Salunke P, Futane S, Sharma M, Sahoo S, Kovilapu U, Khandelwal NK, et al. 'Pseudofacets' or 'supernumerary facets' in congenital Atlanto-axial dislocation: Boon or bane? Eur Spine J 2015;24:80-7.  Back to cited text no. 14
Salunke P, Sahoo SK, Futane S, Deepak AN, Khandelwal NK. 'Atlas shrugged': Congenital lateral angular irreducible atlantoaxial dislocation: A case series of complex variant and its management. Eur Spine J 2016;25:1098-108.  Back to cited text no. 15
Salunke P, Sahoo SK, Deepak AN, Khandelwal NK. Redefining congenital atlantoaxial dislocation: Objective assessment in each plane before and after operation. World Neurosurg 2016;95:156-64.  Back to cited text no. 16
Salunke P. Artificial Atlanto-axial joints: On the “move”. Neurol India 2016;64:275-8.  Back to cited text no. 17
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