Vascular Complications in Cervical Spine Surgery (Anterior and Posterior Approach) STEPHANIE A. DECARVALHO, MUHAMMAD M. ABD-EL-BARR, MICHAEL W. GROFF
HIGHLIGHTS • Vertebral artery injury is the most common type of vascular complication in both anterior and posterior approaches to cervical spine surgery. Vertebral artery injury can occur during exposure, decompression, or instrumentation. • Vertebral artery injury can result in catastrophic bleeding, permanent neurologic damage, and death. • Direct tamponade is the most common method used in the management of vertebral artery injuries, but there are important immediate and delayed consequences of this type of management. Direct repair and endovascular techniques such as embolization and stenting are being used increasingly. • It is imperative that the surgeon studies the preoperative films to avoid these types of injuries, is able to quickly assess when such an injury has occurred, and is able to quickly manage these injuries intraoperatively and the sequelae postoperatively.
Introduction Cervical decompression and instrumentation are common in spinal surgery practice. Vascular complications can occur in both anterior and posterior approaches to cervical spine surgery. Vertebral artery injury (VAI) is the most common type of vascular complication in both approaches. Although rare, VAI can be a life-threatening complication. The incidence of VAI is reported to be 0.08% to 0.5%.1–4 VAI can occur during exposure, decompression, or instrumentation of the cervical spine. The highest reported rates are associated with posterior instrumentation of the high cervical spine (such as C1−2 fusion) and anterior corpectomies.1 As with other surgical complications, it is imperative that the surgeon studies the preoperative films to avoid these types of injuries, is able to quickly assess when such an injury has occurred, and is able to quickly manage these injuries intraoperatively and the consequences postoperatively.
Anatomic Insights Understanding the anatomy of the vertebral artery is critical for the surgeon to avoid VAI injuries and to manage these injuries if 314
they occur. It is critical to study the vertebral artery anatomy in all patients undergoing cervical spine surgeries. Traditional imaging for spine pathology such as magnetic resonance imaging (MRI) or computed tomography (CT) is usually sufficient, but dedicated vascular imaging in the form of MR, CT, or catheter angiography may be helpful in more complex procedures. Normally, the vertebral artery branches off of the first part of the subclavian artery and divides into four segments as it ascends to provide circulation to the posterior fossa and brainstem (Fig. 53.1).5 The first segment, known as V1, starts with the branching of the vertebral artery from the subclavian artery and travels anterior to the transverse foramen of C7 and enters the transverse foramen of C6. The V2 region determines a convergent course of the arteries as it passes through the transverse foramina from C6 to C1. The vertebral artery is typically at least 1.5 mm lateral to the uncovertebral joint.6,7 It is important to note that the vertebral artery may enter the transverse foramen at a level other than C6 in almost 10% of cases.8 The third segment, V3, includes the superior section of the arch of the atlas to the foramen magnum and can be encountered during posterior cervical approaches. It is important to note that as the vertebral artery exits the transverse foramen at C1, it runs medially on the vertebral artery groove (VAG), which is also known as the sulcus arteriosus, and then about 8 to 19 mm from midline and then turns abruptly upward toward the foramen magnum.9 This is especially important during posterior approaches; as such, one should refrain from monopolar cautery when dissecting the ring of C1 laterally, especially along its superior border. The last segment, V4, extends from the foramen magnum to unite with contralateral vertebral artery. The vertebral arteries on either side join to form the basilar artery. Understanding this anatomy should allow surgeons to avoid injuries to the vertebral arteries. In a multiinstitutional survey of spine surgeons, it was found that the most common procedures associated with VAIs are posterior instrumentation of the high (C1−2) spine (34%) and anterior corpectomies (23%), followed by posterior exposures more generally.1 The relatively high rates of vertebral injuries during high cervical instrumentation can be understood by the fact that the vertebral artery has a winding course between C1 and C2, the course through C2 is highly variable, and that much of the instrumentation placed here runs very close to the normal course of the vertebral artery.
CHAPTER 53 Vascular Complications in Cervical Spine Surgery (Anterior and Posterior Approach)
• Fig. 53.1 Gross dissection of the cervical spine demonstrating typical anatomy of the left vertebral artery, including passage anterior to the transverse foramen at C7. The artery subsequently enters the C6 foramen and passes through each successive foramen to C1. (From Grabowski G, Cornett CA, Kang JD. Esophageal and vertebral artery injuries during complex cervical spine surgery–avoidance and management. Orthop Clin North Am. 2012;43:63–74, viii with permission.)
Numerous methods are employed by surgeons for posterior C1−C2 fixation. The most common are Gallie-type fusion,10 transarticular screw placement,11 and C1 lateral mass with C2 pedicle screw (Harms fusion).12 In both transarticular screw placement and C2 pedicle screw placement, the vertebral artery is at risk (Fig. 53.2A and B). Two characteristics that appear to be important in stratifying the risk of VAI during the placement of these screws is the size of the pedicle and the presence of a “highriding” vertebral artery. The exact definition of a high-riding vertebral artery is somewhat vague but refers to the situation when the VAG is too medial and too high within the isthmus of the C2 pedicle to allow for the safe insertion of a C2 pedicle screw (Fig. 53.3).11 It is crucial that the surgeon studies the course of the vertebral artery as it passes through C2 preoperatively for each individual patient before attempting to place C2 pedicle screws. If there is not a good trajectory for placement of a pedicle screw, it is our practice to place a shorter pars screw in C2, which most often provides more than adequate fixation. Several studies have shown that the vertebral artery is less susceptible to injury with C2 pedicle screws compared with transarticular screws,11,13 and as such, we have limited our practice to only C2 pedicle or pars screws. A further benefit of C2 screws is that the trajectory can be modified to accommodate an aberrant course of the vertebral artery without the obligation to traverse the C1–2 joint. Anatomic anomalies increase the likelihood of injury, especially if not appreciated preoperatively. Anomalies can be intraforaminal, extraforaminal, or arterial. Intraforaminal anomalies, also known as vertebral artery tortuosities, occur when the vertebral artery is located medial to the uncovertebral joint. This can cause erosion into the vertebral body, making the vertebral artery susceptible to injury, especially in corpectomy cases.1,14 Extraforaminal anomalies are instances where the vertebral artery traverses anterior to the transverse foramen at levels between C6
B • Fig. 53.2
(A) The trajectory of the transarticular screw is shown. The entry point is set at 3 mm above the C2–C3 joint line and as medial as possible without penetrating the lateral wall of the spinal canal at C2. The screw is angulated as dorsally as possible without perforating the dorsal cortical surface of C2. The vertebral artery groove of C2 is located lateral (black arrowhead) and anteroinferior (white arrowhead) to the screw. (B) The trajectory for the pedicle screw is shown. The entry point is set at the level of the upper end of the C2 lamina. Mediolaterally, it is located at a point that minimizes C2 vertebral artery groove violation, usually at the midportion of the pars interarticularis of C2. Medial and upward angulations are set at an angle that minimizes the groove violation. (From Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013;13:775–785 with permission.)
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• Fig. 53.3
(A) A high-riding vertebral artery is defined by an isthmus height (black asterisk) of 5 mm or less and/or an internal height (white asterisk) of 2 mm or less. (B) A narrow pedicle width is defined by a pedicle width of 4 mm or less (white asterisk). (From Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD. Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J. 2013;13:775–785 with permission.)
and C1. Arterial anomalies include dual-lumen and triple-lumen arteries or a hypoplastic vertebral artery. It is important to note a hypoplastic vertebral artery in the case of VAI because if the injury occurs on the dominant side, neurologic consequences may ensue if sacrifice of the artery is the only method available for management. Carotid injuries during cervical spine surgery are extremely rare. Carotid injuries usually occur in anterior cervical spine surgery. In a retrospective, multicenter review of over 17,000 patients undergoing anterior cervical spine surgery in 21 centers, there were no cases of carotid artery injury (CAI) or cerebrovascular accidents (CVA).15 In a review of the literature, these same authors were able to find only a few cases of carotid injury during anterior cervical procedures. Risk factors for carotid injury appeared to be extensive retraction on the carotid and long operative times.15 Interestingly, in long anterior cervical procedures, it has been shown that the carotid artery may have up to an 80% decrease in its cross-sectional area,16 leading to the suggestion that during long anterior cases, the surgeon should release the retraction on the carotid intermittently.
RED FLAGS • Anomalous anatomy • Copious bright red bleeding • Drop in blood pressure/hemodynamically unstable
Risk Factors • Vertebral artery anomalies. In a large multicenter review of VAIs that involved looking at over 16,000 surgical operations, it was noted that in 50% of VAIs, an anomalous vertebral artery was noted on preoperative imaging.4 This underscores the importance of studying the vertebral artery anatomy preoperatively.
• Abnormal bony anatomy. Most surgeons use bony anatomy as landmarks during cervical spine surgery, and it is crucial to note cases where normal anatomy may be disrupted by degenerative processes, tumors, or other invasive properties.
Prevention Preoperative Prevention Identifying vertebral artery anomalies pre-operatively can reduce the likelihood of injury. Understanding vertebral artery anatomy with an awareness of potential anomalies allows surgeons to avoid injury. For posterior C1−2 fusions, it is critical to identify the presence of a high-riding vertebral artery. For anterior cortectomies a medial deviation of the vertebral artery needs to be accounted for.
Intraoperative Prevention Care should be taken intraoperatively to avoid injury to the vertebral artery. For anterior approaches, it is important to find the midpoint between the longus colli muscles as a landmark for midline as well as the uncovertebral joints bilaterally. This will inform an accurate sense of midline and avoid injury to the laterally positioned vertebral artery during decompression. During foraminal decompression, one should limit the exposure to the uncovertebral joint because this will avoid the vertebral artery in most cases.7 During corpectomies, one should limit the resection of the vertebral body to 16 mm because this will avoid injuring the vertebral artery.17 Particular care should be taken when using a microscope not to create an oblique trajectory and resulting corpectomy trough that would place the contralateral vertebral artery at risk.7 During posterior cervical fusions, especially at C1, C2, the vertebral artery is at risk during both the exposure and the placement of instrumentation. During exposure, care must be taken at the
CHAPTER 53 Vascular Complications in Cervical Spine Surgery (Anterior and Posterior Approach)
superior side of the C1 ring. The venous plexus at C1−2 is particularly challenging, and if great care is not used in this area, profuse venous bleeding may ensue, complicating the establishment of the appropriate starting points for C1, C2 screws and thereby increasing the risk of VAI. As a useful adjunct, we have also used a micro-Doppler to find the carotid and vertebral arteries, especially in cases where normal anatomy is disrupted by tumors intimate with the vasculature.
Management A VAI is usually detected at the time of injury due to bright, copious bleeding that is pressurized.14 Once the VAI is identified, it is crucial for the surgeon to make fast decisions, because patients may lose tremendous amounts of blood in a short period of time. Even so, the dictate primum non nocere is paramount to ensure that the problem is not exacerbated. The first maneuver is to tamponade the bleed and the source with a cottonoid and then to remove as much blood as possible from the surgical field to allow for better visualization. The next maneuver is to try to identify where the injury to the artery has occurred. Due to the extensive bony anatomy around the vertebral artery, this is very difficult and may entail drilling off more bone in the face of copious bleeding. If a distinct hole or tear is found in the vertebral artery, direct repair may be attempted. However, this is often not possible. The use of hemostatic agents such as thrombin mixed with surgical patties may be helpful. However, even if tamponade is successful in decreasing bleeding, there is a greater awareness that this does not constitute a permanent solution, because there are reports of delayed hemorrhages, pseudoaneurysms, and fistulas that can occur with simple tamponade.18–20 Before, during, or after local control has been established, it is important to communicate with the anesthesia members the graveness of the situation so that they may give fluids and blood products to resuscitate the patient. In a delayed fashion, arteriography can further define the injury. In a review of over 16,000 cervical spine cases, in which VAI occurred in only 0.08% of patients, only 23% of those patients required
a transfusion, although the mean blood loss was significant at 770 mL.4 Arterial ligation is also an option but should not be done on dominant vertebral arteries, because significant neurologic consequences have been reported, and an overall mortality of 12% has been documented.21 The canonical recommendation is to follow through with placement of the screw if the injury occurs during drilling of the screw trajectory or tapping. In this way the screw acts as a tamponading instrument. If this method is used, it is advisable not to instrument the contralateral side if it remains undone so as to avoid bilateral injuries to the vertebral arteries. Endovascular techniques should be employed to diagnose the sequelae of the hemostatic and tamponading maneuvers as well as to provide definitive treatment. Even if tamponade is successful in stopping the torrid bleeding of an injury to the vertebral artery, it is advisable that patients who have this type of injury have a vessel angiogram postoperatively. Vessel sacrifice through embolic coils may be attempted if vessel injury is noted,22,23 but again, this is not an option if this injury occurs to the dominant vertebral artery. It also should be noted that ligation or sacrifice of the artery should be done both proximally and distally to the injury site because delayed hemorrhages, fistulas, and pseudoaneurysms have been reported with only proximal ligation.5,18,24 The use of newer stenting technologies is promising,25,26 but these technologies require antiplatelet therapy, which has risks in the immediate perioperative period. Remarkably, despite the high volumes of blood loss that are associated with VAI and the vital structures that the vertebral arteries supply, patients that are managed properly often do well. In a retrospective survey of cervical spine surgeons, they reported that almost 90% of patients that had suffered a VAI had no sequelae or only a temporary neurologic deficit. Five percent had a cerebellar infarct, and 5% mortality was reported.1 In patients that have sustained a VAI, long-term follow-up is encouraged because delayed hemorrhages, pseudoaneurysms, and fistulas have been reported.18,24,27
My Worst Case A 50-year-old female was involved in a motor vehicle versus pedestrian accident. She suffered a traumatic subdural hematoma, pelvic fracture, right hip fracture, and a complicated C2 fracture. The C2 fracture was a combination of a Type III dens fracture, involving the body of C2 (Fig. 53.4A and B), and a hangman’s fracture. On presentation, she was intoxicated but moving all four extremities. She was placed in a cervical orthosis for 4 weeks. Patient continued to have intractable neck pain. Decision was made to undergo a posterior C1−C3 instrumented fusion. The C2 nerve roots were exposed and ligated bilaterally. During tapping of the right C2 pedicle screw, there was significant bleeding. This was tamponaded using Gelfoam (Pfizer Inc., New York, NY) and thrombin. Due to the small size of the right C2 pedicle, it was decided to place a shorter pars screw. Upon placement of the screw, bleeding subsided. Patient woke up neurologically intact. An immediate postoperative CT angiogram of the neck
revealed a pseudoaneurysm adjacent to the C2 pedicle (Fig. 53.4C). Due to patient’s good neurologic status, it was decided to start patient on aspirin (Bayer, Whippany, NJ). On postoperative day 3, patient complained of bilateral lower-extremity weakness and right arm weakness. STAT MRI revealed likely epidural hematoma with cord compression (Fig. 53.4D). Patient was taken to the operating room for evacuation of epidural hematoma and removal of rods. It was felt that some of the compression might be due to the persistent kyphotic deformity, so patient was placed in traction postoperatively. Her neurologic status improved, and a few days later she returned to the operating room for stabilization and replacement of the rods with an in situ fusion. Postoperative MRI revealed no residual cord compression (Fig. 53.4E). Patient was discharged a few days later.
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E • Fig. 53.4
(A and B) A 50-year-old female with complicated dens fracture, including a fracture through the body of the dens (white arrow). Patient underwent C1–3 posterior fusion. During tapping of right C2 pars, significant bleeding was noted that was treated with tamponade and placing of right C2 pars screw. (C) Postoperatively, patient underwent a computed tomography angiogram of the neck that revealed an outpouching of the right vertebral artery, likely representing a pseudoaneurysm (white arrow). Patient was started on aspirin. On postoperative day 3, patient was noted to be weak in the right arm and leg. (D) Magnetic resonance imaging (MRI) revealed cord compression due to kyphotic deformity and epidural hematoma. Patient was taken to the operating room for evacuation of epidural hematoma and removal of rods. Her neurologic status improved, and a few days later she returned to the operating room for replacement of the rods and in situ fusion. (E) Postoperative MRI revealed no residual cord compression (white arrow).
NEUROSURGICAL SELFIE MOMENT Vascular complications during anterior and posterior cervical spine surgery can have drastic consequences. The most common injury is to the vertebral artery, due to its variable course and proximity to areas where instrumentation is placed. It is crucial for the surgeon to prevent these injuries from occurring by studying the preoperative imaging precisely, quickly ascertaining that such an injury has occurred, and managing the injury intraoperatively and monitoring for immediate and delayed sequelae.
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