Overview
Definition:
Vertebral artery exposure, specifically targeting the V3 segment, involves surgically accessing the portion of the vertebral artery as it traverses the transverse foramina of the upper cervical vertebrae and exits the dura mater to form the basilar artery
This segment is crucial for neurovascular surgical approaches to the posterior cranial fossa and upper cervical spine pathologies.
Epidemiology:
The anatomical variations in the vertebral artery course, particularly at its V3 segment, are significant
Understanding these variations is critical in preventing iatrogenic injury during surgery
Incidence of vertebral artery injury during cervical spine procedures ranges from 0.5% to 2.4%, with higher risks in complex reconstructions or tumors involving the foramen magnum.
Clinical Significance:
Iatrogenic injury to the V3 segment of the vertebral artery can lead to devastating neurological deficits, including stroke, paraplegia, or death
Precise anatomical knowledge and meticulous surgical technique are paramount for successful and safe exposure, especially in procedures like anterior cervical decompression, tumor resection at the craniocervical junction, and vertebral artery dissection repair.
Indications
Indications For Exposure:
Direct exposure of the V3 segment is indicated for: surgical repair of vertebral artery injuries (iatrogenic or traumatic)
clipping or coiling of vertebrobasilar junction aneurysms or dissections
resection of tumors involving the artery or surrounding structures (e.g., meningiomas, glomus tumors, chordomas)
and access for bypass procedures in cases of severe stenosis or occlusion.
Relative Indications:
Relative indications may include visualization for embolization procedures or during complex anterior suboccipital approaches where the artery requires mobilization or temporary occlusion for better surgical field access.
Contraindications:
Absolute contraindications are rare but include severe coagulopathy, active systemic infection, or extensive atherosclerotic disease precluding safe manipulation
Relative contraindications might involve significant comorbidities affecting surgical risk.
Preoperative Preparation
Preoperative Imaging:
Essential imaging includes CTA or MRA of the head and neck to delineate the vertebral artery course, identify anatomical variations, assess for aneurysms, dissections, or atherosclerotic lesions, and evaluate collateral circulation
Digital subtraction angiography (DSA) may be required for detailed assessment and planning of interventional procedures.
Neurological Assessment:
A thorough preoperative neurological examination is crucial to establish a baseline for comparison with the postoperative status, paying close attention to cranial nerve function, motor strength, sensation, and cerebellar signs.
Anesthesia Considerations:
General anesthesia with controlled hypotension and meticulous hemodynamic monitoring is typically employed
Intraoperative neuromonitoring, including somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs), may be used to assess the integrity of the corticospinal tract and posterior columns
Transcranial Doppler (TCD) can monitor flow within the artery.
Informed Consent:
Comprehensive informed consent must detail the risks, including neurological injury, stroke, bleeding, infection, CSF leak, and the potential need for blood transfusion or further procedures.
Surgical Approach And Technique
General Approach:
The V3 segment is typically accessed via an anterior or anterolateral cervical approach, extending superiorly towards the skull base
For the V3 segment, a higher approach, often a modified anterolateral suboccipital approach, is frequently utilized, involving dissection through the posterior triangle of the neck.
Dissection And Identification:
Dissection proceeds along the carotid sheath and scalene muscles to identify the common carotid artery, from which the internal carotid and external carotid arteries arise
The vertebral artery originates from the subclavian artery and ascends through the transverse foramina of C6 to C1
The V3 segment is identified as it exits the C1 (atlas) transverse foramen and arches posteriorly and medially to enter the cranial cavity via the foramen magnum.
V3 Segment Exposure:
Careful dissection around the C1 transverse foramen and the atlanto-occipital membrane is required
The artery then traverses the subarachnoid space before forming the basilar artery
Identification of the artery as it ascends and courses medially is critical
Mobilization must be gentle to avoid intimal injury.
Arterial Control And Manipulation:
Temporary occlusion may be achieved using atraumatic vascular clamps or vessel loops
Proximal control is usually obtained on the subclavian artery or at the origin of the vertebral artery from the subclavian
Distal control is achieved as it enters the dura or forms the basilar artery
Careful dissection from surrounding venous structures and nerve roots (e.g., cranial nerves IX, X, XI, XII) is essential.
Reconstruction Techniques:
In cases of repair, primary anastomosis, interposition grafting (e.g., saphenous vein, radial artery), or end-to-end anastomosis may be employed
If primary repair is not feasible or the risk of re-dissection is high, a bypass graft from the carotid artery or a suitable donor vessel to a more distal segment of the vertebral artery or basilar artery may be necessary.
Postoperative Care
Neurological Monitoring:
Close neurological observation is paramount
Any new or worsening neurological deficit requires immediate investigation
Serial neurological examinations are performed frequently.
Hemodynamic Management:
Maintaining adequate blood pressure is crucial to ensure perfusion to the brain and prevent thrombosis
Vasopressors may be needed to maintain mean arterial pressure (MAP) above 90 mmHg, especially if temporary occlusion was prolonged or flow is compromised.
Antithrombotic Therapy:
Anticoagulation (e.g., heparin) may be initiated postoperatively, followed by antiplatelet agents (e.g., aspirin, clopidogrel) depending on the surgical intervention and risk of thrombosis or embolization
Duration and type of therapy are individualized.
Wound Care And Pain Management:
Standard wound care, including dressing changes and monitoring for signs of infection, is essential
Pain management should be adequate to ensure patient comfort and facilitate mobilization
Management of potential CSF leaks also requires attention.
Complications
Vascular Complications:
Major complications include vertebral artery dissection, thrombosis, embolization leading to stroke (posterior circulation infarcts), pseudoaneurysm formation, arteriovenous fistula, and acute hemorrhage from the surgical site.
Neurological Complications:
Neurological deficits can range from cranial nerve palsies (e.g., hypoglossal, vagal, accessory) to brainstem or cerebellar stroke, resulting in motor weakness, sensory loss, ataxia, or dysphagia
Spinal cord injury is rare but possible with extensive dissection.
Other Complications:
Other complications include infection, CSF leak, phrenic nerve palsy, Horner's syndrome, and difficulties with swallowing or speech due to manipulation of surrounding structures
Delayed complications can include graft failure or late aneurysm formation.
Key Points
Exam Focus:
Understanding the anatomical landmarks of the V3 segment, especially its relationship with the C1 transverse foramen and the foramen magnum
Knowledge of potential pitfalls and complications during dissection and manipulation
Familiarity with indications for vertebral artery repair and reconstructive techniques.
Clinical Pearls:
Always obtain proximal and distal control before manipulating the vertebral artery
Gentle dissection is key to avoid intimal injury
Maintain adequate cerebral perfusion pressure postoperatively
Consider embolization of a damaged segment only if repair is not feasible and collateral flow is adequate.
Common Mistakes:
Failure to identify anatomical variations, aggressive dissection leading to intimal tear, inadequate proximal/distal control, misinterpreting intraoperative monitoring, and suboptimal postoperative anticoagulation strategies.