Surgical Nuances for Safeguarding Anomalous Vertebral Artery during Atlantoaxial/Occipital-C2 Fixation in Complex CV Junction Pathologies: Operative Video Article

Abstract

Nearly one-fifth of craniovertebral junction (CVJ) pathologies are associated with anomalous vertebral arteries (VAs), posing a significant surgical challenge. The VA can be damaged during dissection or screw placement. Eight patients with CVJ pathology and anomalous VA underwent instrumented fusion (C1-C2/O-C2). A comprehensive preoperative radiological evaluation with intraoperative biplanar fluoroscopy and Doppler was utilized for VA localization and screw placement. A postoperative computed tomography (CT) cervical spine with VA angiography was performed to assess the VA status and screw placement. Analysis revealed atlas assimilation/segmentation bony anomalies in all patients. The variations of anomalous VA included fenestrated V3 VA, C2 segmental VA, and high-riding VA, either alone or in combination. Few patients demonstrated bilateral anomalous VA. All cases had C1-C2 joints drilled and opened. C1 lateral mass–C2 pedicle fusion was performed in 6/8 and O-C2 pedicle fusion in 2/8 cases. All cases except one had spacer insertion. There was no injury to the anomalous VA. One patient required spacer revision due to malposition. Utilizing preoperative three-dimensional CT angiography to identify anomalous VA, meticulous surgical dissection on the normal side first, experienced assisting surgeon, identification of C2 nerve root ganglion, and intraoperative Doppler, we aim to enhance the safety and efficacy of CV J fixation procedures, leading to improved patient outcomes. Mobilization of the anomalous vessel is essential to facilitate the safe drilling of the facets and the accurate placement of screws and spacers under direct visualization. Strict compliance with the above techniques ensures rigid fusion in the presence of an anomalous VA.

Keywords

craniovertebral junction - atlantoaxial dislocation - anomalous vertebral artery - C1-C2 fixation - operative nuances

Introduction

The craniovertebral junction (CVJ), a complex anatomical region, encompasses critical neurovascular structures and poses unique biomechanical challenges, making it a key focus in neurosurgical practice. The pursuit of short-segment, biomechanically robust fixation, however, inadvertently increases the risk of vertebral artery (VA) injury, especially in the presence of anomalous VA anatomy.[1] [2] [3] Such anomalies may obstruct the safe placement of lateral mass screws, with any attempt potentially resulting in catastrophic intraoperative VA injury.

Among the reported anomalous VAs, V3 segment anomalies may reach up to 10%. When coupled with the anomalous anatomy of CVJ, the optimal entry point for C1 and C2 needs to be redefined, accounting for the anatomical dissection of the anomalous VA.[4] [5] Accurate identification of the anomalous VA in the preoperative imaging is crucial for the surgical fixation involving C1 and C2 to avoid intraoperative VA injury. Advancements in techniques have made the surgery around the VA much safer, and these include fluoroscopy, O-arm, intraoperative computed tomography (CT) scan, neuronavigation, and three-dimensional (3D) printing.[6] [7] [8] [9] In low-resource settings, especially in low-middle-income countries and very low-income countries, there is limited access to this advanced technology. There is even limited access to preoperative 3D CT angiography and intraoperative Doppler. These resource constraints could be due to inadequate infrastructure, the absence of trained personnel, or restricted financial support for the patients to cover the cost of surgery. These restrictions might make the identification of the VA preoperatively and intraoperatively difficult, often increasing the risk of injury to the VA.

Earlier techniques proposed to mitigate intraoperative VA injury were screw tightening to achieve hemostasis, the usage of sublaminar hooks, or extending fixation to adjacent levels. While these methods are helpful during the early neurosurgical career of performing CVJ surgeries, they often result in less rigid constructs, suboptimal bony fusion, and an increased risk of VA injury or erosion during screw placement.[3] A thorough understanding of the operative nuances involved in safely dissecting these vessels is crucial to improving surgical outcomes in patients with CVJ pathology.

This video article presents eight cases of complex CVJ pathologies with associated VA anomalies and illustrates key surgical techniques for the safe dissection of these vessels and the successful achievement of instrumented fusion. It is hypothesized that a detailed understanding of these surgical approaches can lead to better patient outcomes in CVJ procedures.

Inclusion/Exclusion Criteria

Inclusion Criteria

Inclusion criteria were patients with congenital CVJ anomaly requiring fixation performed by posterior cervical approach and identification of the anomalous VA by preoperative CT angiogram.

Exclusion Criteria

Patients < 10 years, patients with nonavailability of preoperative CT angiogram of no anomalous VA course, and patients undergoing anterior fixation rather than posterior C1-C2 fixation were excluded. Further, patients with traumatic CVJ anomaly, lack of postoperative imaging and follow-up, and prior CVJ surgery were also excluded to avoid the potential confounders.

Case Discussion

Eight patients with complex CVJ pathology with anomalous VA were included in the present study over the last year. The demographics, presenting complaints, and the imaging findings are discussed in detail and presented in [Table 1]. All patients underwent preoperative magnetic resonance imaging (MRI) CVJ with brain and spine screening, along with 3D CT angiography. The V3 segment of VA was studied in detail. In addition, the type of atlantoaxial dislocation (AAD), C1-C2 joint alignment, C1 lateral mass, and C2 pedicle/facets were observed and recorded. An intraoperative Doppler was utilized in all the cases to visualize and locate the anomalous VA. The joints were drilled in all the cases except one, where the aberrant bony anatomy and the anomalous VA precluded the joint dissection. The joint spacer was placed in all cases except one. The course, type of anomalous VA, caliber, and dominance were identified preoperatively in all the cases ([Table 2]). A follow-up imaging was performed in all the cases to assess screw placement, VA caliber, and patency. Preoperative planning, intraoperative anatomy, biplanar fluoroscopy, and dissection guided the screw placement. The aim was to provide short, stable, biomechanical robust fixation in the form of C1 lateral mass and C2 transpedicular. It was successfully performed in 6 out of 8 cases. In the remaining two cases, the aberrant bony abnormalities precluded the placement of lateral mass screws. All the cases were followed annually, and the outcome of independent mobilization (Nurick's classification) and bony fusion was assessed.

Table 1 Demographics and imaging findings

	Age (y)	Gender	Symptoms	CV junction bony pathology	Brainstem compression	Syrinx
Case 1	14	Male	Neck pain, torticollis, restricted neck movements with clicking sounds, spastic quadriparesis	Os odontoideum, AAD - anterior facetal dislocation C1-C2 joints - vertical C1 lateral mass - occipitalized atlas C2 pedicles/facets - normal	Yes	No
Case 2	35	Female	Neck pain, cough headache, sensory paresthesias, decreased pain sensation C5-C7 dermatomes bilaterally, brisk reflexes, bulbar symptoms - hoarseness of voice, vocal cord palsy, regurgitation of food contents	Bifid posterior arch C1 AAD - central instability C1-C2 joints – horizontal pBC2 > 9 mm C1 lateral mass - partial occipitalized atlas C2 pedicles/facets - normal	Yes, tonsillar herniation, brainstem elongation	Yes
Case 3	29	Female	Neck pain, clicking sounds, spastic hemiparesis, brisk reflexes, Hoffman positive	Atlantoaxial dislocation with invagination AAD - anterior facetal dislocation C1-C2 joints – oblique to vertical C1 lateral mass -occipitalized atlas C2 pedicles/facets – right isthmic, left normal	Yes	No
Case 4	14	Male	Neck pain, torticollis, jerk movements, spasticity, brisk reflexes, Hoffman positive	Atlantoaxial dislocation - lateral, retroflexed odontoid AAD - lateral dislocation C1-C2 joints – right oblique, left horizontal C1 lateral mass -occipitalized atlas C2 pedicles/facets – right isthmic, left borderline isthmic	Yes	No
Case 5	14	Male	Neck pain and tilt, new onset spastic quadriparesis, Hoffman positive	Bifid atlas AAD - rotatory dislocation C1-C2 joints – right vertical, left horizontal C1 lateral mass – aberrant bony anatomy precludes safe placement of lateral mass screws C2 pedicles/facets – bilateral isthmic	Yes	Yes
Case 6	29	Male	Torticollis, new onset spastic quadriparesis, Hoffman positive	AAD - rotatory dislocation with BI C1-C2 joints – right oblique, left horizontal C1 lateral mass – occipitalized atlas, aberrant bony anatomy precludes safe placement of lateral mass screws C2 pedicles/facets – bilateral borderline isthmic	Yes	Yes
Case 7	44	Female	Grip clumsiness and progressive weakness for 2 years, left spastic hemiparesis for 6 months	AAD - rotatory dislocation with BI C1-C2 joints – right vertical, left horizontal C1 lateral mass – occipitalized atlas C2 pedicles/facets – bilateral Isthmic	Yes	Yes
Case 8	35	Male	Spastic quadriparesis, sensory paresthesia, Hoffman positive	AAD - rotatory dislocation with BI C1-C2 joints – horizontal C1 lateral mass – occipitalized atlas C2 pedicles/facets – right borderline isthmic, left normal	Yes	Yes

Abbreviations: AAD, atlantoaxial dislocation; BI, basilar invagination; CV, craniovertebral.

Table 2 Anomalous VA and surgical findings

	Anomalous VA		Caliber/dominance	C1-C2 fixation	O-C2 fixation	Joint spacer	Intraop injury VA	Postop complications	Joint drilled	C2 ganglion preserved	Outcome pain, spasticity, Nurick's pre/post	Bony fusion
	Right	Left
Case 1	Fenestrated V3 VA	Normal course through bony Canal in occipitalized atlas	Codominant	Yes	No	Yes, bilateral with bone	None	Spacer malposition – required revision surgery	Yes	No	Resolution of neck pain, 5/3	Yes
Case 2	C2 segmental VA	Normal course	Right dominant	Yes	No	Yes – right side – with bone, on left side – only bone	None	None	Yes	No	Resolution of neck pain, 2/2, cranial nerve palsy - improvement	Yes
Case 3	C2 segmental VA, HRVA	Normal course V3 VA, HRVA	Codominant	Yes	No	Yes, bilateral with bone	None	None	Yes	No	Resolution of neck pain, 4/3	Yes
Case 4	C2 segmental VA - dominant	C2 segmental VA – hypoplastic	Right dominant	Yes	No	Yes, bilateral	None	None	Yes	Yes	Resolution of neck pain, 5/3	Yes
Case 5	C2 segmental VA, HRVA	Normal course	Right dominant	No	Yes	No	None	None	No	Yes on right side	Resolution of neck pain, spasticity improved, 4/3	Yes
Case 6	C2 segmental VA	Aplastic	Right dominant	No	Yes	Yes, bilateral	None	None	Yes	No	Spasticity improved, 4/3	Yes
Case 7	HRVA	Normal course	Right dominant	Yes	No	Yes, bilateral	None	None	Yes	No	Spasticity improved, 4/3	Yes
Case 8	C2 segmental VA	Normal course	Right dominant	Yes	No	Yes, bilateral	None	None	Yes	Yes toward the normal side	Spasticity improved, 5/3	Yes

Abbreviations: HRVA, high-riding vertebral artery; VA, vertebral artery.

Results

The present study includes patients from the age range of 14 to 44 years, including 3 females and 5 males. The presenting complaints included neck pain, click sounds on neck movement, torticollis, spastic hemiparesis or quadriparesis, brisk reflexes, presence of pathological reflexes, sensory paresthesia, and bulbar weakness. Out of 8 patients, patient 2 presented with signs of syringomyelia—cough headaches and signs of bulbar weakness—hoarseness of voice, and vocal cord palsy. The atlas was occipitalized in 7/8 cases. The joints were oblique to vertical in 6/8 cases on the side of the anomalous VA. In 2/8 cases, the bilateral C1-C2 joints were found to be horizontal. In 2/8 cases, bilateral atlantoaxial joint alignment was oblique to vertical. In 4/8 cases, rotatory AAD was present, anterior facetal dislocation in 2/8 cases, lateral dislocation in 1/8 cases, and central instability in 1/8 cases. The C2 pedicles/facets were found to be abnormal in the majority of the cases of the present study. In 6/8 cases, the C2 pedicle was found to be isthmic (height of isthmus of C2 measured 3 mm lateral to the lateral border of the spinal canal of less than 5 mm) and more predominant on the side of the anomalous VA. In addition to the bony CVJ abnormality, brainstem compression was present in all of the cases. The syrinx was present in more than 50% of the cases ([Table 1]).

The most common anomalous V3 VA identified in the present series was C2 segmental VA, identified in 6/8 cases. The C2 segmental VA exits the transverse foramen from C2, travels posterior to the C1-C2 joint, and then enters the foramen magnum to become intradural. Other anomalies identified included high-riding VA (HRVA) and fenestrated V3 VA, type 3 Wang anomalous VA (between bony canal of fused occiput and C1 lateral mass), hypoplastic VA, and aplastic VA (type IV Wang), etc. A bilateral anomalous V3 VA was identified in 4/8 cases. In 2/8 cases, the anomalous V3 VA (C2 segmental artery) was associated with ipsilateral HRVA. In all of the cases, the right side presented with the anomalous V3 VA, and it was dominant in 6/8 cases. In the remaining, codominance was observed ([Table 2]).

The goal was to achieve a short, stable, biomechanical robust construct in all patients with CVJ abnormalities and anomalous VA. A C1-C2 fixation was performed in 6/8 cases, and O-C2 fixation was performed in the remaining cases. The O-C2 fixation was performed in view of aberrant bony abnormality that precluded the safe placement of the lateral mass screws. The atlantoaxial joints were opened and drilled in 7/8 cases. In all the cases where the joint was opened and drilled, a metal spiked joint spacer augmented with autologous bone was inserted between the joints for distraction and fusion. With the increasing experience of the surgeon, every effort was made to save the C2 ganglion/nerve root to avoid postoperative numbness. The C2 ganglion was preserved in 3/8 cases. There were no intraoperative VA injuries. Except for one patient requiring reexploration surgery for spacer malposition, no other postoperative complications were reported in the present series. All patients were followed for 1 year after their surgery, and outcomes were reported in the form of Nurick's grading and assessment of the bony fusion. In all the patients, neck pain, spasticity, weakness, and bulbar involvement were resolved throughout follow-up. The mean Nurick's grade before and after the surgery was 4.125 versus 2.875. Bony fusion was achieved in all the cases ([Table 2]).

Table 3 Dissection technique and screws

	Anomalous VA		Caliber/dominance	Dissection technique	Screws
	Right	Left
Case 1	Fenestrated V3 VA	Normal course through bony canal in occipitalized atlas	Codominant	Foramen magnum decompression before joint distraction, sharp dissection, intraoperative Doppler, identification of C2 ganglion as a consistent landmark, medialization of anomalous VA, coagulation of the fenestrated branch V3 VA	C1–lateral mass C2–bilateral transpedicular
Case 2	C2 segmental VA	Normal course	Right dominant	Sharp dissection, intraoperative Doppler, identification of C2 ganglion as a consistent landmark, safe mobilization of anomalous VA medially and inferiorly for joint drilling and spacer insertion	C1 - lateral mass – usage of shank screws on side of anomalous VA, long length of lateral mass screw to match the level of C2 pedicle screw C2–bilateral transpedicular
Case 3	C2 segmental VA, HRVA	Normal course V3 VA, HRVA	Codominant	Foramen magnum decompression before joint distraction, sharp dissection, intraoperative Doppler, identification of C2 ganglion as a consistent landmark, mobilization of anomalous VA using rubber loop medially and inferiorly for joint drilling and spacer insertion	C1–lateral mass - usage of shank screws on side of anomalous VA, long length of lateral mass screw to match the level of C2 pedicle screw C2–right high entry (isthmic crest summit) transpedicular, left transpedicular
Case 4	C2 segmental VA - dominant	C2 segmental VA – hypoplastic	Right dominant	Foramen magnum decompression before joint distraction, intra-operative Doppler, C2 ganglion and bilateral anomalous VA mobilized inferiorly and medially due to laxity of the ligaments	C1–lateral mass - usage of shank screws on side of anomalous VA, long length of lateral mass screw to match the level of C2 pedicle screw C2–bilateral high entry (isthmic crest summit) transpedicular
Case 5	C2 segmental VA, HRVA	Normal course	Right dominant	Foramen magnum decompression, intraoperative Doppler, individual occipital plate for easier rod manipulation	Occipital plate – individual on each side C2–bilateral high-entry (isthmic crest summit) transpedicular
Case 6	C2 segmental VA	Aplastic	Right dominant	Foramen magnum decompression before joint distraction, intraoperative Doppler, C2 ganglion sacrifice, sharp dissection, mobilization of anomalous VA for joint drilling and spacer insertion	Midline occipital plate – aberrant bony anatomy precludes lateral mass screw placement. C2–right high entry (isthmic crest summit) transpedicular, left C1-C2 high-entry transarticular
Case 7	HRVA	Normal course	Right dominant	Foramen magnum decompression before joint distraction, C2 ganglion sacrifice	C1–lateral mass - long length of lateral mass screw to match the level of C2 pedicle screw C2–bilateral high-entry (isthmic crest summit) transpedicular
Case 8	C2 segmental VA	Normal course	Right dominant	Foramen magnum decompression before joint distraction, intraoperative Doppler for VA localization, mobilization of anomalous VA for joint drilling and spacer insertion	C1–lateral mass - long length of lateral mass screw to match the level of C2 pedicle screw, drilling of overhang of occiput to access the lateral mass, usage of shank screws on side of anomalous VA C2–right high-entry (isthmic crest summit) transpedicular, left transpedicular, usage of shank screws on side of anomalous VA

Abbreviations: HRVA, high-riding vertebral artery; VA, vertebral artery.

Operative Nuances/Video Transcript

The patient is placed in a prone position with the head fixed with Gardner traction. A 10-lb weight is applied to maintain a floating position. The head and legs are elevated. All pressure points are adequately padded. A baseline, lateral fluoroscopic image is obtained. A midline linear incision extends from the inion to the C3 spinous process. A subperiosteal dissection is done to reflect the muscle and expose the C2 spinous process ([Table 3]).

Case 1: A 14-year-old male presented with complaints of neck pain, torticollis, restricted neck movements with clicking sounds, and spastic quadriparesis. Imaging revealed Os odontoideum, anterior facetal dislocation, bilateral vertical C1-C2 Joints, occipitalized atlas, and normal bilateral C2 pedicles. MRI showed brainstem compression without syrinx formation. CT angiography showed a right V3 fenestrated VA and type III Wang VA on the left side. Intraoperative Doppler confirms a C2 segmental artery on the right side. Foramen magnum decompression (FMD) is performed using the Kerrison rongeurs and the cutting drill given severe cervicomedullary compression. The C2 ganglion is identified, which is sharply dissected, coagulated, and cut. The C2 ganglion forms an important landmark for the identification of the anomalous VA. The anomalous VA usually lies posterior to the C1-C2 joint and anterior to the C2 ganglion. The fenestrated branch of the V3 VA is identified using the Doppler, which is then coagulated, divided, and clipped. Once the FMD and anomalous VA dissection are done, the bilateral joints are distracted using the Penfield dissector. The drill holes for C2 transpedicular screws are tapped under fluoroscopic guidance. The C2 segmental artery is protected by medial retraction with the Penfield dissector during the hole tapping. This is followed by joint drilling to make vertical joints favorable for metal-spiked spacer insertion. The C1 lateral mass screws are inserted after the spacer insertion followed by rod placement and tightening under reduction. A sound probe is used to rule out any breach in the cortex while tapping the holes. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the technique of FMD before joint distraction, utilization of sharp dissection, usage of intraoperative Doppler, identification of C2 ganglion as a consistent landmark, medialization of anomalous VA, and coagulation of the fenestrated branch V3 VA ([Video 1]).

Download Video

Video 1 Patient Positioning & Operative Nuances in Cases 1 & 2.

Case 2: A 35-year-old female presented with complaints of neck pain, Valsalva headache, sensory paresthesias, decreased pain sensation in C5-C7 dermatomes bilaterally, brisk reflexes, and bulbar symptoms—hoarseness of voice, vocal cord palsy, and regurgitation of food contents. Imaging revealed a bifid posterior arch, central atlantoaxial instability, horizontal C1-C2 joints, pBC2 > 9 mm, a partially occipitalized atlas, and normal bilateral C2 pedicle. MRI showed brainstem elongation and compression, tonsillar herniation with syrinx formation. CT angiography showed a right dominant C2 segmental artery with a left normal course of V3 VA. The C2 segmental artery complex with the C2 ganglion is identified on the right side. Sharp dissection is started to separate the ganglion from the anomalous VA. Intraoperative Doppler confirms a C2 segmental artery on the right side. With the help of the Penfield dissector, the anomalous VA is lifted from the C2 ganglion, and sharp dissection is continued to separate the ganglion from the artery. In a traumatic CVJ pathology or one without overt abnormal bony abnormality, every effort should be made to preserve the C2 ganglion. In the present case, the C2 ganglion is sacrificed to access the C1-C2 joints and C1 lateral mass. Once the anomalous VA is dissected, it can be mobilized inferiorly and medially for drilling the hole in the lateral mass and opening up the joint space. The occipital overhang is adequately drilled to access the C1 lateral mass and to achieve adequate screw trajectory. These few millimeters of space provide visualization of the lateral mass and an adequate trajectory for the C1 lateral mass. A failure to drill would result in abnormal angulation of the drill guide and risk injuring the anomalous VA. This is followed by tapping the holes in the C1 lateral mass and C2 pedicle on the anomalous VA side (right) and the normal side. The assistant should retract the mobilized VA at all times, as failure to do so would risk a fatal injury to the anomalous VA. The C2 pedicle screw is inserted under fluoroscopic guidance, and the bilateral joints are drilled. The joints are distracted using metal-spiked spacers filled with autologous bone followed by insertion of C1 lateral mass screws. As shown, the screws are placed on the normal side first followed by on the anomalous VA side. A shank screw or a partially threaded screw is used for C1 lateral mass so that the smooth part of the screw does not erode or irritate the anomalous VA adventitia. In addition, the length of the C1 screw should be long so that both C1 and C2 lie at the same level for the rod placement and adequate reduction. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the technique of sharp dissection for anomalous VA, usage of intraoperative Doppler, identification of C2 ganglion as a consistent landmark, safe mobilization of anomalous VA, and drilling of the overhang of occiput to provide easy access to C1 lateral mass for screw placement ([Video 1]).

Case 3: A 29-year-old female presented with complaints of neck pain, clicking sounds, spastic hemiparesis, brisk reflexes, and positive pathological reflexes—Hoffman sign. Imaging revealed an AAD with basilar invagination, anterior facetal dislocation, oblique to vertical bilateral C1-C2 joints, occipitalized atlas, and a right C2 isthmic pedicle. MRI showed brainstem compression. CT angiography showed a codominant right C2 segmental artery with an ipsilateral HRVA and a left HRVA with a normal V3 VA course. Sharp dissection is performed to identify the C2 segmental artery complex with the C2 ganglion on the right side. The dissection is continued to separate the ganglion from the anomalous VA. Intraoperative Doppler confirms a C2 segmental artery on the right side. The C2 ganglion is coagulated and divided. The anomalous VA is dissected and mobilized inferiorly and medially for drilling the hole in the lateral mass and opening up the joint space. A rubber loop is passed around the artery for retraction. Before opening the joint space and distracting the joints, FMD is done using the cutting drill, Kerrison and Leksell rongeurs. Intraoperative distraction is done to open the joints for drilling using the vertebral body distractor placed between the occiput and the C2 spinous process. The joints are drilled using a 40-mm diamond drill bit followed by hole tapping for the C1 and C2 pedicular screws. For an adequate C2 pedicular trajectory, always place the suction toward the medial border of the superior articular facet, which helps guide the surgeon regarding the medial trajectory, and the craniocaudal trajectory can be appreciated from the biplanar fluoroscopy. In this case, a right high entry (isthmic crest summit) transpedicular screw was inserted given the right isthmic C2 pedicle. The dissected anomalous VA can be seen freely mobilized cranially and inferiorly for spacer insertion and C1 lateral mass insertion, respectively. It should be noted that while anomalous VA is dissected freely, every maneuver should be done after safely retracting the VA as shown in the video with the use of Penfield dissector No. 4. The usage of shank screws (partially threaded) is advocated if the anomalous VA is anticipated to be in contact with the screw stem. The video also highlights that the surgeon rely on the importance of the bony fusion rather than the screw rod construct by inserting the pieces of autologous bone in addition to the metal-spiked spacers. The rods are placed and tightened after adequate reduction. Intraoperative Doppler confirms the patency of the anomalous VA. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the technique of FMD before joint distraction, sharp dissection of the anomalous VA, usage of intraoperative Doppler, identification of C2 ganglion as a consistent landmark, mobilization of anomalous VA using rubber loop medially and inferiorly for joint drilling and spacer insertion, usage of suction placed at the medial border of the isthmus to serve as a guide for medial trajectory of the C2 transpedicular screw, and avoid medial cortex breach. In case of isthmic C2 pedicle, it is advocated to use a high/superior entry transpedicular screw. Neuronavigation, if available, is advisable; however, it does not substitute for the surgeon's clinical experience ([Video 2]).

Download Video

Video 2 Operative Nuances in Cases 3, 4 & 5.

Case 4: A 14-year-old male presented with complaints of neck pain, torticollis, jerk movements, spasticity, brisk reflexes, and positive pathological reflexes—Hoffman sign. Imaging revealed a lateral AAD with retroflexed odontoid, a right oblique and left horizontal C1-C2 joint, occipitalized atlas, and bilateral C2 isthmic pedicle. MRI showed brainstem compression. CT angiography showed a bilateral C2 segmental artery with right dominance. FMD is done using the cutting drill and Kerrison rongeurs. The laxity of the ligaments and the preoperative traction helped in opening up the joints and providing adequate space for joint dissection, drilling, and tapping the drill holes in the C1 lateral mass and C2 pedicle. Drill holes were tapped on the side with a hypoplastic C2 segmental artery in the C1 lateral mass and a C2 high-entry isthmic crest. Intraoperative Doppler confirms a dominant C2 segmental artery on the right side. A left high entry C2 pedicle screw is inserted followed by spacer insertion and then followed by a left C1 lateral mass screw insertion. The C2 ganglion and bilateral anomalous VA are mobilized inferiorly and medially. Due to laxity, there was space for C1 lateral mass dissection and hole tapping. Hence, both the C2 ganglions were preserved. On the side with dominant anomalous VA, a high-entry C2 pedicle screw is inserted followed by spacer and lateral mass screw insertion. The rod is placed and tightened under reduction. Intraoperative Doppler confirms the patency of the anomalous VA. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the technique of FMD before joint distraction, usage of intraoperative Doppler, identification of C2 ganglion as a consistent landmark, and laxity of the ligaments allowed for easy manipulations of the C2 ganglion and anomalous VA complex. In case of isthmic C2 pedicle, it is advocated to use a high/superior entry transpedicular screw ([Video 2]).

Case 5: A 14-year-old male presented with complaints of neck pain, torticollis, spastic quadriparesis, and presence of pathological reflexes—Hoffman sign positive. Imaging revealed a bifid atlas, rotatory AAD with severe basilar invagination, a right vertical and left horizontal C1-C2 joint, and bilateral C2 isthmic pedicle. MRI showed brainstem compression. CT angiography showed a right dominant C2 segmental artery with ipsilateral HRVA. The left side VA follows a normal course. FMD is done using the cutting drill and Kerrison rongeurs. Intraoperative Doppler confirms a dominant C2 segmental artery on the right side. Due to severe basilar invagination and aberrant bony abnormality, the occiput and C2 spinous process are distracted using the vertebral body dissector as shown. The C2 ganglion is sacrificed on the left side. A bilateral high-entry C2 pedicle hole is tapped using the drill. The bleeding can be controlled using a Spongostan rolled and inserted into the tapped hole as shown here. The severe aberrant bony abnormality and the presence of the dominant anomalous VA posterior to the C1-C2 joint precluded the C1 lateral mass screw insertion. The spacer was not inserted on the left side as it would exacerbate the torticollis. Bilateral high-entry C2 pedicle screws are inserted under fluoroscopic guidance. This is followed by fixation of the individual occipital plate for easier rod manipulation and reduction. Intraoperative Doppler confirms the patency of the anomalous VA. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the usage of intraoperative Doppler for identification of the anomalous VA, usage of individual occipital plate for easier rod manipulation, intraoperative decision for occipital–C2 fixation in view of difficult anatomy and risk of jeopardizing the anomalous VA, and usage of high-entry C2 pedicle screws for C2 isthmic pedicle ([Video 2]).

Case 6: A 29-year-old male presented with complaints of torticollis, spastic quadriparesis, and presence of pathological reflexes—Hoffman Sign positive. Imaging revealed rotatory AAD with basilar invagination, a right oblique and left horizontal C1-C2 joint, occipitalized atlas, and bilateral C2 isthmic pedicle. MRI showed brainstem compression with syrinx formation. CT angiography showed a right dominant C2 segmental artery. The left side VA is aplastic. FMD is done using the cutting drill and Kerrison rongeurs. Intraoperative Doppler confirms a dominant C2 segmental artery on the right side. The C2 ganglion is identified as a consistent landmark lying posterior to the anomalous VA. Dissection is performed to separate and mobilize the V3 anomalous VA on the right side. The vertebral venous plexus surrounding the VA usually bleeds, which can be controlled using bipolar coagulation. The joints are opened, drilled, and distracted using the metal-spiked spacers. It is followed by placement of midline occipital plate and placement of right high-entry transpedicular screw and left C1-C2 high entry transarticular screw. The severe aberrant bony abnormality and the presence of the dominant anomalous VA posterior to the C1-C2 joint precluded the C1 lateral mass screw insertion. Intraoperative Doppler confirms the patency of the anomalous VA. The postoperative scan shows reduction of basilar invagination with adequate placement of the screws and patent anomalous VA. The case highlights the usage of intraoperative Doppler for identification of the anomalous VA, identification of C2 ganglion as a consistent landmark, intraoperative decision for occipital–C2 fixation in view of difficult anatomy and risk of jeopardizing the anomalous VA, mobilization of the VA for joint drilling and spacer insertion, and usage of high-entry C2 pedicle screws for C2 isthmic pedicle ([Video 3]).

Download Video

Video 3 Operative Nuances in Cases 6, 7 & 8.

Case 7: A 44-year-old female presented with complaints of grip clumsiness and progressive weakness for 2 years, and left spastic hemiparesis for 6 months. Imaging revealed rotatory AAD with basilar invagination, a right vertical and left horizontal C1-C2 joint, occipitalized atlas, and bilateral C2 isthmic pedicle. MRI showed brainstem compression with syrinx formation. CT angiography showed a right dominant HRVA. The left side artery is normal. FMD is done using the cutting drill and Kerrison rongeurs. The bilateral C2 ganglion is sacrificed. Occiput and C2 spinous processes are distracted by the vertebral body dissector. The left side C1-C2 joint is opened, distracted, and drilled. The same process is repeated on the anomalous VA side. The distraction of the C1-C2 joint is always done after adequate foramen decompression is done to avoid traction injury to the brainstem. This is followed by insertion of the metal-spiked spacer in the bilateral C1-C2 joint. Drill holes are tapped in the bilateral C1 lateral mass and C2 pedicle. A bilateral C2 high-entry (isthmic crest summit) transpedicular screw is inserted due to isthmic pedicle C2. This is followed by rod placement and screw tightened under reduction. The postoperative scan shows adequate reduction and placement of the screws. The case highlights the importance of FMD before joint mobilization and distraction. In addition, it highlights the usage of high-entry C2 pedicle screws for C2 isthmic pedicle so as to not compromise on biomechanical strength of the construct ([Video 3]).

Case 8: A 35-year-old male presented with complaints of spastic quadriparesis, sensory paresthesia, and positive pathological reflexes—Hoffman sign. Imaging revealed a rotatory AAD with basilar invagination, bilateral horizontal C1-C2 joints, occipitalized atlas, and right C2 isthmic pedicle with a left normal C2 pedicle. MRI showed brainstem compression with syrinx formation. CT angiography showed a right dominant C2 segmental artery with a left normal course VA. The normal side is dissected first. The C2 ganglion is dissected and preserved. The occipital overhang is drilled to expose the C1 lateral mass on the normal side. It helps in exposure and aiding the trajectory of the C1 lateral mass screw. Drill hole are tapped for C1 lateral mass and C2 transpedicular screws. The C1-C2 joint is opened on the normal side first. Dissection is carried out toward the anomalous VA side. Sharp dissection is done for the anomalous VA. Intraoperative Doppler confirms a dominant C2 segmental artery on the right side. The C2 ganglion is identified as a consistent landmark posterior to the anomalous VA, which is coagulated and cut. Sharp dissection is done to dissect the anomalous VA. Occipital bone overhang soft tissue is cleared using bipolar coagulation and then sharply divided using 11 no. surgical blade. The dissected anomalous VA is retracted using the Penfield dissector. The occipital overhang is drilled, and then the hole is tapped in the C1 lateral mass under fluoroscopic guidance. On the right side, a high-entry C2 pedicular screw is tapped followed by metal-spiked spacer. The shank screws are used bilaterally to avoid erosion of the VA on the right side and the irritation of the C2 ganglion on the left side. The rods are connected and the screw is tightened under reduction. The postoperative scan shows reduction of AAD with adequate placement of the screws and patent anomalous VA. The case highlights the usage of intraoperative Doppler, identification of C2 ganglion as a consistent landmark, preservation of C2 ganglion, usage of high/superior entry transpedicular screw for C2 isthmic pedicle, mobilization of anomalous VA for joint drilling and spacer insertion, drilling of overhang of occiput to access the lateral mass, and usage of shank screws on the side of anomalous VA ([Video 3]).

Key Message

• CT angiography is quintessential for preoperative planning and identification of anomalous VA.

• Identification of the C1 lateral mass, C2 pedicle, and atlantoaxial joint orientation is important in surgical planning and achieving a robust short construct.

• Monopolar cautery should be avoided and only used at a low current setting if required.

• In cases with severe basilar invagination (BI) and brainstem compression, FMD should be performed before joint drilling and distraction to avoid brainstem injury.

• The normal side should be dealt with first, as it helps in distracting the joints and provides more space to dissect the anomalous VA and do the joint dissection on the anomalous side.

• Intraoperative Doppler should be utilized in all cases with anomalous VA and complex CVJ bony abnormalities.

• C2 ganglion forms a reliable and consistent landmark for the identification of the anomalous VA.

• Sharp dissection should be carried out to dissect the VA from the surrounding C2 ganglion and the vertebral venous plexus.

• The anomalous VA should be dissected first before the joint distraction to avoid any iatrogenic injury.

• The aim of the construct should be short, biomechanically robust in the form of C1 lateral mass and C2 transpedicular.

• In cases with occipitalized atlas, the overhang of the occiput should be drilled/flattened to provide adequate space and angulation for C1 lateral mass screw drilling.

• In case of isthmic C2 pedicle, a high-entry transpedicular (isthmic crest summit) can be an alternative option.

• In case of isthmo-internal C2 pedicle, C2-3 transfacetal or C2 laminar screw should be considered.

• The ultimate goal of the surgery is to provide bony fusion rather than the placement of the screw-rod construct.

• In case of anomalous VA, usage of shank screws or partially threaded screws is advisable.

• The endplates of the C1-C2 joint should be adequately drilled to promote bony fusion.

• A postoperative CT angiography is advisable to assess the VA patency and the screw placement ([Video 3]).

Discussion

Surgical procedures at the CVJ aim to decompress neural structures, realign the spine, and provide stabilization. VA is a vital structure that closely follows the contours of the atlantoaxial facet joints, and its anatomical relationship is crucial for both understanding cervical spine function and minimizing surgical risks. Embryologically, the VA is formed by longitudinal anastomosis of the first to sixth intersegmental arteries. The horizontal portion is formed by the proatlantal artery. However, the absence of proatlantal and persistence of the second dorsal segmental artery running alongside the C2 ganglion leads to the formation of the C2 segmental artery, which enters the dura below the C1. Failure of regression of the second dorsal segmental artery leads to a fenestrated V3 VA.[10] According to Uchino et al, the overall prevalence of VA anomalies at the CVJ is 5.0%, with about 11% of these anomalies being bilateral.[11] Anomalous VAs are more frequently discovered in conjunction with congenital skeletal abnormalities that impact the CVJ.[3] [12]

Radiological evaluation of the CVJ abnormalities requires a dedicated MRI CVJ with T2 sagittal sequence along with 3D CT angiography of cervical spine to evaluate the bony anatomy, sagittal and coronal alignment of cervical spine, orientation of C1-C2 joints, C1 lateral mass, C2 facets, isthmus and pedicle, along with 2D/3D multiplanar reconstruction of the VA from C6 foramen to intradural segment. Various anomalies of the VA have been described in the literature. However, the anomalies pertinent to the CVJ include the HRVA and the V3 segment VA anomalies. Various classifications have been proposed in the literature. However, the most useful for classification of the VA from a surgical view point includes the following—Klepinowski et al classification of HRVA into isthmic, internal, and isthmo-internal, Wang et al classification of anomalous VA to occipitalized atlas, and Tokuda et al classification of V3 VA into C2 segmental artery, fenestrated V3 VA, and extradural posterior inferior cerebellar artery.[10] [12] [13]

The HRVA global prevalence is 25.3%, with a higher incidence in patients with rheumatoid arthritis.[14] [15] It is defined as a pedicle width of less than 4 mm, C2 isthmus height of less than 5 mm, and C2 internal height of less than 2 mm measured 3 mm lateral to the lateral border of the spinal canal.[16] Klepinowski et al in a retrospective observational study analyzed 454 subjects with 918 insertion sites and classified HRVA into three following subtypes: isthmic with C2 isthmus height of less than 5 mm, internal with C2 internal height of less than 2 mm, and isthmic-internal with C2 isthmus and internal height less than 5 and 2 mm, respectively. The incidence of type isthmic, internal, and isthmic-internal HRVA was 78.2, 8.8, and 12.9, respectively. The narrow pedicle of < 4 mm was found in 73.9% of isthmic, 53.8% of internal, and 100% of isthmic-internal HRVA.[13]

Wang et al classified V3 VA to occipitalized atlas. Embryologically, failure of segmentation of the fourth occipital and first cervical sclerotome results in an occipitalized atlas. It accounts for nearly 33% of all the bony CVJ abnormalities. The type 1 (8.3%) runs beneath the occipitalized posterior arch and the lateral mass. The type 2 (25%) runs beneath the occipitalized arch but at the level of the lateral mass. Types 1 and 2 are comparable to the C2 segmental artery of the Tokuda classification. In type 3 (61.1%), the VA runs in the osseous canal between the occipital bone and the occipitalized atlas. Type 4 (5.6%) includes complete aplasia of the VA.[12] Accurate identification of these anatomical variations is essential in surgical planning, enabling a safer approach to instrumentation.

The treatment decisions were based on radiological instability, neural compression, presence of myelopathy, or progressive symptoms. Asymptomatic patients without neural compression, preserved cord morphology, and stable CVJ were placed under radiological surveillance. We suggest posterior instrumentation fixation and decompression. Except in a few cases, which show no improvement after the above, proceed with ventral decompression. The AAD with or without BI are mobile and unstable. All joints are manually reducible. They are not fixed deformities. The surgical decision is based on joint orientation, assimilation of C1 lateral mass, VA anomaly type, and bony feasibility of safe screw placement. [Fig. 1] illustrates a stepwise algorithm for choosing between C1-C2 and O-C2 fixation.

Fig. 1 A stepwise treatment algorithm for managing non-traumatic CVJ abnormality and choosing between C1-C2 and O-C2 fixation.

In cases with anomalous VA with severe BI and brainstem compression, FMD should be performed before joint drilling and distraction to avoid brainstem injury. Intraoperative Doppler should be utilized in all cases with anomalous VA and complex CVJ bony abnormalities. During dissection, the monopolar cautery should be avoided and should only be used at a low current setting if required. C2 ganglion forms a reliable and consistent landmark for the identification of the anomalous VA. It lies posterior to the anomalous vessel. The normal side should be dealt with first, as it helps in distracting the joints and provides more space to dissect the anomalous VA and do the joint dissection on the anomalous side.[5] Additionally, in cases where the abnormal side cannot be dissected safely or the VA gets injured, the stabilization of CVJ is achieved partially. Sharp dissection should be carried out to dissect the VA from the surrounding soft tissue, the C2 ganglion, and the vertebral venous plexus. The bleeding from the venous plexus can be controlled using bipolar coagulation. The anomalous VA should be dissected first before the joint distraction to avoid any iatrogenic injury. Adequate mobilization of the anomalous VA is essential to prevent intraoperative avulsion/shearing injury of the VA from the fixed point at the C2 transverse or at the intradural entry point. Once freed, the anomalous VA can be mobilized using a rubber loop/Penfield dissector medially and inferiorly for joint drilling and spacer insertion. In cases with fenestrated V3 VA, the fenestrated branch can be coagulated.

The aim of the construct should be short, biomechanically robust in the form of C1 lateral mass and C2 transpedicular. In cases with occipitalized atlas, the overhang of the occiput should be drilled/flattened to provide adequate space and angulation for C1 lateral mass screw drilling. These few millimeters of space provide visualization of the lateral mass and an adequate trajectory for the C1 lateral mass. A failure to drill would result in abnormal angulation of the drill guide and risk injuring the anomalous VA. The length of C1 lateral mass should be long to match the polyaxial head of the C2 pedicle screw for rod placement and adequate reduction. An occipital plate can be used if aberrant anatomy precludes lateral mass screw placement. The C2 screw options include transpedicular, pars, transarticular, superior entry transpedicular, C2 inferior facet, subfacetal, C2 − C3 transfacetal, and translaminar screws. For a normal artery course, a transpedicular provides the highest pull-out strength. In case of isthmic HRVA, a superior entry transpedicular/high-entry (summit of isthmic crest) transpedicular screw advocated by Beucler is advisable.[17] In case of internal HRVA, short pars screw or a C2-3 transfacetal is to be considered. In isthmic-internal, options include C2-3 transfacetal or translaminar screws.[13] For an adequate C2 pedicular trajectory, it is advisable to place the suction toward the medial border of the superior articular facet, which helps guide the surgeon regarding the medial trajectory, and the craniocaudal trajectory can be appreciated from the biplanar fluoroscopy. When the hole is drilled under the biplanar fluoroscopy, bleeding from the drill hole can be controlled by packing with long Spongostan as demonstrated in cases 1 and 5 ([Videos 1] and [2]).

The ultimate goal of the surgery is to provide bony fusion rather than the placement of the screw-rod construct. The endplates of the C1-C2 joint should be adequately drilled to promote bony fusion. In case of anomalous VA, usage of shank screws or partially threaded screws is advisable to prevent VA erosion or dissection. A postoperative CT angiography is advisable to assess the VA patency and the screw placement. Intraoperative navigation systems can enhance precision in screw placement, further minimizing the risk of injury. However, it does not substitute for the surgeon's clinical experience. Utilizing modalities such as Doppler ultrasound and indocyanine green angiography allows for immediate assessment of VA integrity during surgery.[18] The relative contraindications to instrumentation include anomalous VA with an intraosseous course that preclude safe dissection, dominant anomalous VA with associated significant joint deformity precluding safe placement of screws, significant occipital overhang precluding lateral mass access, severe condylar and lateral mass hypoplasia, and patient comorbidities. High-risk scenarios included bilateral anomalies and extremely narrow isthmic-internal pedicles.

All cases in the study underwent a refined surgical approach, emphasizing precise anatomical alignment and robust fixation techniques to enhance stability and minimize complications. Although combined anterior-posterior approaches have been described, we advocate a posterior-only approach even in anomalous VA cases, provided adequate exposure and joint drilling are feasible. Compared to combined approaches, posterior-only instrumentation safely allows joint reduction and fusion; it is less morbid and allows for safer dissection with minimal manipulation of neurovascular structures.[19] [20] [21] [22] [23] In early experience, surgeons should operate with an experienced mentor and avoid aggressive dissection in anomalous VA cases. Using navigation, Doppler, and starting with the normal side are strongly recommended. Complex cases with bilateral anomalies or isthmic pedicles should be referred to high-volume centers. Successful execution of these surgical techniques necessitates advanced imaging (CT angiography), intraoperative Doppler, biplanar fluoroscopy, and a skilled surgical team. Resource-constrained settings must prioritize institutional training and equipment investment. Cadaveric dissections, 3D-printed vascular models, and hands-on fellowships are instrumental in training for these cases. Development of national-level CVJ simulation modules and certification pathways can improve surgical safety and consistency. Intraoperative navigation can further refine surgical precision and reduce complications. While our approach is feasible in tertiary centers with advanced imaging and experienced surgical teams, its core principles, viz., identifying anomalous anatomy, respecting dissection planes, and preoperative planning, remain relevant across varied health care environments.

Limitations

This was a video-based observational study of a rare cohort of anomalous VA in CVJ fixation surgery. CVJ anomaly requiring fixation with an anomalous VA is not a very common entity. Therefore, a formal power analysis for the sample size justification was not done. However, further studies with a larger sample size and possible multicentric collaboration will be beneficial to address the generalizability and validity of the techniques mentioned in the present article.

Conclusion

Utilizing preoperative 3D CT angiography to identify anomalous VA, meticulous surgical dissection on the normal side first, an experienced assisting surgeon, identification of C2 nerve root ganglion, and intraoperative Doppler, we aim to enhance the safety and efficacy of CVJ fixation procedures, leading to improved patient outcomes. Mobilization of the anomalous vessel is essential to facilitate the safe drilling of the facets and the accurate placement of screws and spacers under direct visualization. Strict compliance with the above techniques ensures rigid fusion in the presence of an anomalous VA.

Conflict of Interest

None declared.

Acknowledgments

We would like to thank Dr. Sonia Baral and Ms. Meenali Mittal for their contributions to the artwork, and Dr. Abhishek Shetty for collecting the patient data.

Patients' Consent

Full and detailed consent from the patient/guardian has been taken. The patients' identity has been adequately anonymized. If anything related to the patients' identity is shown, adequate consent has been taken from the patient/relative/guardian. The journal will not be responsible for any medico-legal issues arising out of issues related to the patients' identity or any other issues arising from the public display of the video.

Authors' Contributions

The conception and design of the work were carried out by A.S. and A.M. Data collection was performed by A.M., H.P., M.B., and P.G., while data editing and analysis were conducted by R.M., H.P., and P.G. The initial drafting of the article was completed by H.P., A.M., and A.A., and the critical revision of the manuscript was undertaken by A.S., R.M., and A.A. The final version of the article was reviewed by A.M.

• References

• 1 Lopez AJ, Scheer JK, Leibl KE, Smith ZA, Dlouhy BJ, Dahdaleh NS. Anatomy and biomechanics of the craniovertebral junction. Neurosurg Focus 2015; 38 (04) E2
• 2 Song G-C, Cho K-S, Yoo D-S, Huh P-W, Lee S-B. Surgical treatment of craniovertebral junction instability : clinical outcomes and effectiveness in personal experience. J Korean Neurosurg Soc 2010; 48 (01) 37-45
• 3 Yamazaki M, Okawa A, Furuya T. et al. Anomalous vertebral arteries in the extra- and intraosseous regions of the craniovertebral junction visualized by 3-dimensional computed tomographic angiography: analysis of 100 consecutive surgical cases and review of the literature. Spine 2012; 37 (22) E1389-E1397
• 4 Muthukumar N. Problems in instrumentation of syndromic craniovertebral junction anomalies - case reports. Neurospine 2019; 16 (02) 277-285
• 5 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 (01) 5-10
• 6 Du Y-Q, Qiao G-Y, Yin Y-H, Li T, Tong H-Y, Yu X-G. Usefulness of 3D printed models in the management of complex craniovertebral junction anomalies: choice of treatment strategy, design of screw trajectory, and protection of vertebral artery. World Neurosurg 2020; 133: e722-e729
• 7 Randazzo M, Pisapia JM, Singh N, Thawani JP. 3D printing in neurosurgery: a systematic review. Surg Neurol Int 2016; 7 (Suppl. 33) S801-S809
• 8 Salmi M, Paloheimo K-S, Tuomi J, Wolff J, Mäkitie A. Accuracy of medical models made by additive manufacturing (rapid manufacturing). J Craniomaxillofac Surg 2013; 41 (07) 603-609
• 9 Çokkeser Y, Naguib MB, Kizilay A. Management of the vertebral artery at the craniocervical junction. Otolaryngol Head Neck Surg 2005; 133 (01) 84-88
• 10 Tokuda K, Miyasaka K, Abe H. et al. Anomalous atlantoaxial portions of vertebral and posterior inferior cerebellar arteries. Neuroradiology 1985; 27 (05) 410-413
• 11 Uchino A, Saito N, Watadani T. et al. Vertebral artery variations at the C1-2 level diagnosed by magnetic resonance angiography. Neuroradiology 2012; 54 (01) 19-23
• 12 Wang S, Wang C, Liu Y, Yan M, Zhou H. Anomalous vertebral artery in craniovertebral junction with occipitalization of the atlas. Spine 2009; 34 (26) 2838-2842
• 13 Klepinowski T, Żyłka N, Pettersson SD. et al. Types of high-riding vertebral artery: a classification system for preoperative planning of C2 instrumentation based on 908 potential screw insertion sites. Spine J 2025; 25 (01) 59-68
• 14 Klepinowski T, Pala B, Cembik J, Sagan L. Prevalence of high-riding vertebral artery: a meta-analysis of the anatomical variant affecting choice of craniocervical fusion method and its outcome. World Neurosurg 2020; 143: e474-e481
• 15 Klepinowski T, Cembik J, Sagan L. Risk of the high-riding variant of vertebral arteries at C2 is increased over twofold in rheumatoid arthritis: a meta-analysis. Neurosurg Rev 2021; 44 (04) 2041-2046
• 16 Neo M, Matsushita M, Iwashita Y, Yasuda T, Sakamoto T, Nakamura T. Atlantoaxial transarticular screw fixation for a high-riding vertebral artery. Spine 2003; 28 (07) 666-670
• 17 Beucler N. The summit of the isthmic crest of the axis as a new entry point for C2 pedicle screw: an anatomical study. Neurosurg Rev 2024; 47 (01) 107
• 18 Lee DH, Park JH, Lee JJ. et al. Intraoperative surveillance of the vertebral artery using indocyanine green angiography and Doppler sonography in craniovertebral junction surgeries. Neurosurg Focus 2021; 50 (01) E5
• 19 Jain VK, Behari S, Banerji D, Bhargava V, Chhabra DK. Transoral decompression for craniovertebral osseous anomalies: perioperative management dilemmas. Neurol India 1999; 47 (03) 188-195
• 20 Jian F-Z, Chen Z, Wrede KH, Samii M, Ling F. Direct posterior reduction and fixation for the treatment of basilar invagination with atlantoaxial dislocation. Neurosurgery 2010; 66 (04) 678-687 , discussion 687
• 21 Guo SL, Zhou DB, Yu XG, Yin YH, Qiao GY. Posterior C1-C2 screw and rod instrument for reduction and fixation of basilar invagination with atlantoaxial dislocation. Eur Spine J 2014; 23 (08) 1666-1672
• 22 Chandra PS, Prabhu M, Goyal N, Garg A, Chauhan A, Sharma BS. Distraction, compression, extension, and reduction combined with joint remodeling and extra-articular distraction: description of 2 new modifications for its application in basilar invagination and atlantoaxial dislocation: prospective study in 79 cases. Neurosurgery 2015; 77 (01) 67-80 , discussion 80
• 23 Goel A. Treatment of basilar invagination by atlantoaxial joint distraction and direct lateral mass fixation. J Neurosurg Spine 2004; 1 (03) 281-286

Publication History

Article published online:
22 January 2026