|Year : 2021 | Volume
| Issue : 4 | Page : 1-3
Aberrant Vertebral Artery and Screw Placement in Lateral Mass of C1 in Atlantoaxial Fixation
J K. B. C Parthiban
Kovai Medical Centre Hospital, Coimbatore, Tamil Nadu, India
|Date of Submission||25-Oct-2021|
|Date of Acceptance||26-Oct-2021|
|Date of Web Publication||24-Dec-2021|
J K. B. C Parthiban
Kovai Medical Centre Hospital, Civil Aerodrome Post, Coimbatore - 641 014, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Aberrant vertebral arteries at C1 and C2 facet regions are rare. These vessels can pose challenges while inserting screws into the lateral mass. However, mobilization of these vessels is possible to obtain specific screw entry points. In normal bony anatomy, these aberrant vessels are tortuous and hence can be mobilized quickly. Multiple screw entry points are available for safe screw placement. Aberrant vessels at this region do not preclude the placement of screws in lateral mass.
Keywords: Aberrant artery, lateral mass screw, screw entry point, segment 3 vertebral artery
|How to cite this article:|
Parthiban J K. Aberrant Vertebral Artery and Screw Placement in Lateral Mass of C1 in Atlantoaxial Fixation. J Spinal Surg 2021;8:1-3
|How to cite this URL:|
Parthiban J K. Aberrant Vertebral Artery and Screw Placement in Lateral Mass of C1 in Atlantoaxial Fixation. J Spinal Surg [serial online] 2021 [cited 2022 Aug 11];8:1-3. Available from: http://www.jossworld.org/text.asp?2021/8/4/1/333617
| Introduction|| |
Segmental fixation of C1 (atlas) and C2 (axis) is the most sought after technique in the recent past in managing craniovertebral junction (CVJ) pathologies. Ever since the screw techniques were innovated, the old-fashioned wiring techniques and extension of fixations to the cranium have taken a back seat. However, every new technique improves our knowledge in biomechanics, regional bony and vascular anatomy, use of newer imaging technology, and newer surgical skill. Hence, nothing comes out for granted. Surgeons who try to innovate and advance need to improve their knowledge to newer heights in perfecting these techniques, reducing complications, and achieving better results than the older techniques.
| Imageology|| |
The most crucial step is to understand the bony and vascular anatomy of CVJ, particularly at facet joints of C1 and C2, before embarking on surgery. In normal circumstances, the lateral mass of C1, facet joint, and C2 superior facet, pedicle, pars, and inferior facet may be normal in anatomy. Still, there is always a chance of encountering an aberrant vertebral artery at the V3 segment in 5% of cases. Conventional computed tomography (CT) scans can show us the anatomical variations in vertebral foramen that indicates a possible anomalous vertebral artery in the vicinity. If the indentations of the vascular groove are deep and tortuous, indeed warns of a very risky abnormal artery. The investigation of choice in preoperative planning of C1/2 screw stabilization is CT-angiography with three-dimensional (3D) reconstruction images. This newer technology and CT sequences provide excellent anatomical details of the vascular anatomy concerning the bones where the screws need to be placed. Tortuosity, aberrant nature, size, and relation to C1/C2 facet joint and bony structure can be studied in detail, and surgical planning can be done preoperatively with great comfort. This single modality of imageology is worth doing to avoid surprises and devastating complications encountered when attempting to do C1/2 fixation. Magnetic resonance imaging angiography may be of help to an extent but may not replace CT angiography with 3D reconstruction.
| Aberrant Vessels|| |
There are three most common varieties of the aberrant V3 segment of vertebral artery worth mentioning, namely (1) an aberrant vertebral artery that courses dorsally to the C1/2 joint and enters ventral to C1 arch, which is a persistent first intersegmental artery [Figure 1] and (2) extracranial origin of posterior inferior cerebellar artery that courses along with the aberrant vertebral artery as mentioned earlier. Here, both vessels lay dorsal to the C1/2 joint and (3) duplicated V3 segment, one was passing through the normal course entering the foramen in C2 and anterior to C1 arch. The other is aberrant that courses dorsal to C1/2 facet and enters ventral to C1 arch to join the previous one to form V4 segment [Figure 2]. This duplicated version forms a loop around the C1 arch and is varied in size and tortuosity. These abnormal vessels can be easily and meticulously mobilized and retracted in normal bony anatomy while securing the C1 lateral mass screw.
|Figure 1: Aberrant segment three vertebral arteries coursing dorsal and over the facet joint. A rudimentary vessel is seen in the normal course as well|
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|Figure 2: Duplicated aberrant segment three vertebral arteries seen over the facet joint, course under C1 lamina and joins the normal course vessel to form segment 4|
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| Technique|| |
To avoid vertebral artery injury, surgeons should avoid using monopolar cautery of any type and sharp knives for any reason. Small subperiosteal elevators, blunt smooth curved dissectors, low bipolar sharp cautery, and blunt round-tipped micro scissors are the instruments of my choice at this region to dissect soft tissues from bone (identify the screw entry point) and dissect the artery along with soft tissues around it as a protective layer. Dissection should go smoothly and meticulously with 3D CT angio guidance. Once these disciplines are followed, there is no fear in handling aberrant vertebral arteries. Rarely does one need an ultrasound for this.
| Screw Entry Points|| |
The lateral mass of C1 is a strong cylindrical bone with superior and inferior facets. The classical Goel's point of screw entry is from the midpoint of the dorsal surface of lateral mass below the posterior arch (lamina), and this needs good dissection and often C2 ganglion resection. Aberrant loops can be mobilized to use this entry point. Tans's translaminar entry point is created by decorticating the posterior arch over lateral mass. Lee's notching technique describes drilling the inferior aspect of the arch (lamina) at the midpoint of lateral mass. These entry points can be used as and when needed depending on the aberrant vessel in the region [Figure 3]. Often one hardly needs to dissect away the tortuous loops if these entry points are judiciously selected. Hong has described superior lateral mass entry points to avoid aberrant vessel dissection altogether. Keeping the screw head in the correct position can avoid vessel compression. This editorial presents a lateral mass screw placed through an entry point mid-way between Tan's and Lee's entry point [Figure 4]. The aberrant vessel needs to be retracted to prepare the screw entry point and easily insert a 3.5-mm screw.
|Figure 3: Screw entry points in lateral mass of C1: G – Goel's point (sub laminar midlateral mass), T -Tan's point (Trans laminar), L- Lee's point (infra laminar notch). On the right side, the entry point of the present case is marked|
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|Figure 4: (a) Aberrant branch (black arrow) is seen below C1 lamina over (dorsal) C1/2 facet joint. (b) A notch is drilled at the inferior border of the C1 lamina at the midpoint of the lateral mass. Aberrant branch retracted inferiorly. (c) A sharp probe is entered through the notch entry point directed anteriorly, superiorly, and medially in lateral mass of C1. (d) A 3.5-mm polyaxial screw is secured. The superior border of C1 lamina was not breached. This is more of a combination of the notch and inferior laminar entry points. Aberrant vessel just retracted and not relocated|
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Complex bony anatomy in congenital lesions such as assimilation of C1 with occiput, odontoid invagination, high riding vertebral artery with deep grooves in bony architect may make the situation difficult for placing screws in C1 lateral mass. However, aberrant vessels do not preclude screw placement. It is wise to avoid taking much risk close to the vessels, but one can try alternative screw positioning in appropriate available bone mass in the CVJ.
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Conflicts of interest
There are no conflicts of interest.
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