The V1 and V2 Segment of the Vertebral Artery: Surgery Around the Cervical Vertebral Bodies Bernard George, MD, Oscar Alves, MD, and Alexandre Carpentier, MD Surgical exposure and control of the first (V1) and second (V2) segments of the vertebral artery (VA) permit lesions in the vicinity of the VA, causing compression, to be treated. Surgical exposure also improves access to the posterolateral corner of the vertebral bodies and to the anterior part of the spinal canal. Tumoral and nontumoral lesions may compress the VA. Tu- moral lesions usually cause permanent compression of the VA and need to be removed surgically regardless of the severity of the compression. Nontumoral lesions cause intermittent com- pression and require surgery only if they are symptomatic and markedly reduce the VA diameter. The surgical technique in- volves gaining proximal and distal control of the VA before proceeding with decompression. An oblique corpectomy provides access to the posterolateral corner of the cervical spine and to the anterior part of the spinal canal. The VA is exposed before the lateral aspect of the verte- bral bodies is drilled to reach the posterior ligament, dural sac, or both while preserving most of the vertebral bodies. This tech- nique is primarily used to decompress the anterior aspect of the spine in spondylotic myelopathy. It is also used to enlarge the intervertebral foramen to resect intra- and extraspinal tumors (neurinomas). Copyright 2002, Elsevier Science (USA). All rights reserved. S urgical exposure and control of the first (V1) and second (V2) segments of the vertebral artery (VA) permit lesions near the VA causing compression to be treated and improve access to the posterolateral corner of the cervical vertebral bod- ies and consequently to the anterior part of the cervical spinal canal (oblique corporectomy). External Compression of the V2 The VA can be compressed by different external factors (Table 1), among which intermittent and permanent factors must be differentiated, t-5 From the Department of Neurosurgery, H6pital Lariboisi6re, Paris, France. Address reprint requests to Bernard George, Department of Neurosur- gery, H6pital Lariboisiere,2 rue Ambroise Pare, 75010 Paris, France, Tel: 33 1-49-95-81-46, Fax: 33 1-49-95-81-55, E-mail: bernard.george@lrb. ap-hop-paris.fr Copyright 2002, Elsevier Science (USA). All rights reserved. 1092-440X/02/0501-0002535.00/0 doi:l 0.1053/otns.2002.0000 TABLE 1. Extrinsic Factors Compressing Vl and V2 in 118 Casest Cause Decompression Revascularization Tumors 103 2 Osteophytes 5 Fibrous bands 4 1 Nerve 1 Trauma 2 1-Authors' personal series. Intermittent Factors Intermittent factors tend to be nontumoral lesions that cause transitory compression during a specific movement of the head, neck, or both. 6-12 On imaging (typically angiography) the movement that produces the VA compression must be the same as the one that produces the patient's symptoms (Fig 1). Be- cause symptoms are subjective (ie, dizziness, blurred vision, vertigo), this criterion is mandatory to determine the need for surgical resection of compressive elements. The most common intermittent cause of VA compression is osteophytic spurs that compress the VA during contralateral rotation of the head. 9,~3-17 Fibrous bands are another cause of VA compression, typically during extension of the neck (Fig 2). ls-22 Fibrous bands are fibrous thickening of the longus colli tendon, which crosses the anterior aspect of the VA when it enters the transverse canal at an abnormal level. During neck extension, the transverse pro- cesses project the VA anteriorly while the fibrous bands hinder its displacement, producing a cigar cut effect on it. A similar pathology is observed at C1-C2. It is common in Japan where it has been described as "bow hunter's syndrome". 8,23,24 Other lesions have also been reported: disc herniation, 25 head or spine injury, 26-3~ sympathetic nerve at the level of V17 (Fig 3), C2 nerve root at CI-C2, 7 bone malformation of the craniocervical junction, 7 and even tumor as reported in the case of an aneu- rysmal cyst at C4. 31 Permanent Factors Permanent compression displaces the VA but seldom reduces its diameter significantly; therefore, it seldom affects vertebro- basilar flow and produces no symptoms. Most factors causing permanent VA compression are tumors. The more or less slow growth of tumors provides sufficient time for collateral blood flow to develop even in cases of complete occlusion. 32 Many types of tumors develop in the vicinity of the VA. The most common are neurinomas with an hourglass form (Fig 4).33-36 These neurinomas originate in the foramina and extend along the nerve in two directions: medially into the foramen Operative Techniques in Neurosurgery, Vol 5, No 1 (March), 2002: pp 25-49 25
Transcript
The V1 and V2 Segment of the Vertebral Artery: Surgery Around the Cervical Vertebral Bodies
Bernard George, MD, Oscar Alves, MD, and Alexandre Carpentier, MD
Surgical exposure and control of the first (V1) and second (V2) segments of the vertebral artery (VA) permit lesions in the vicinity of the VA, causing compression, to be treated. Surgical exposure also improves access to the posterolateral corner of the vertebral bodies and to the anterior part of the spinal canal.
Tumoral and nontumoral lesions may compress the VA. Tu- moral lesions usually cause permanent compression of the VA and need to be removed surgically regardless of the severity of the compression. Nontumoral lesions cause intermittent com- pression and require surgery only if they are symptomatic and markedly reduce the VA diameter. The surgical technique in- volves gaining proximal and distal control of the VA before proceeding with decompression.
An oblique corpectomy provides access to the posterolateral corner of the cervical spine and to the anterior part of the spinal canal. The VA is exposed before the lateral aspect of the verte- bral bodies is drilled to reach the posterior ligament, dural sac, or both while preserving most of the vertebral bodies. This tech- nique is primarily used to decompress the anterior aspect of the spine in spondylotic myelopathy. It is also used to enlarge the intervertebral foramen to resect intra- and extraspinal tumors (neurinomas). Copyright 2002, Elsevier Science (USA). All rights reserved.
S urgical exposure and control of the first (V1) and second (V2) segments of the vertebral artery (VA) permit lesions
near the VA causing compression to be treated and improve access to the posterolateral corner of the cervical vertebral bod- ies and consequently to the anterior part of the cervical spinal canal (oblique corporectomy).
External Compression of the V2
The VA can be compressed by different external factors (Table 1), among which intermittent and permanent factors must be differentiated, t-5
From the Department of Neurosurgery, H6pital Lariboisi6re, Paris, France.
Address reprint requests to Bernard George, Department of Neurosur- gery, H6pital Lariboisiere, 2 rue Ambroise Pare, 75010 Paris, France, Tel: 33 1-49-95-81-46, Fax: 33 1-49-95-81-55, E-mail: bernard.george@lrb. ap-hop-paris.fr
Copyright 2002, Elsevier Science (USA). All rights reserved. 1092-440X/02/0501-0002535.00/0 doi:l 0.1053/otns.2002.0000
TABLE 1. Extrinsic Factors Compressing Vl and V2 in 118 Casest
Intermittent factors tend to be nontumoral lesions that cause transitory compression during a specific movement of the head, neck, or both. 6-12 On imaging (typically angiography) the movement that produces the VA compression must be the same as the one that produces the patient's symptoms (Fig 1). Be- cause symptoms are subjective (ie, dizziness, blurred vision, vertigo), this criterion is mandatory to determine the need for surgical resection of compressive elements. The most common intermittent cause of VA compression is osteophytic spurs that compress the VA during contralateral rotation of the head. 9,~3-17 Fibrous bands are another cause of VA compression, typically during extension of the neck (Fig 2). ls-22 Fibrous bands are fibrous thickening of the longus colli tendon, which crosses the anterior aspect of the VA when it enters the transverse canal at an abnormal level. During neck extension, the transverse pro- cesses project the VA anteriorly while the fibrous bands hinder its displacement, producing a cigar cut effect on it. A similar pathology is observed at C1-C2. It is common in Japan where it has been described as "bow hunter's syndrome". 8,23,24 Other lesions have also been reported: disc herniation, 25 head or spine injury, 26-3~ sympathetic nerve at the level of V17 (Fig 3), C2 nerve root at CI-C2, 7 bone malformation of the craniocervical junction, 7 and even tumor as reported in the case of an aneu- rysmal cyst at C4. 31
Permanent Factors
Permanent compression displaces the VA but seldom reduces its diameter significantly; therefore, it seldom affects vertebro- basilar flow and produces no symptoms. Most factors causing permanent VA compression are tumors. The more or less slow growth of tumors provides sufficient time for collateral blood flow to develop even in cases of complete occlusion. 32
Many types of tumors develop in the vicinity of the VA. The most common are neurinomas with an hourglass form (Fig 4).33-36 These neurinomas originate in the foramina and extend along the nerve in two directions: medially into the foramen
Operative Techniques in Neurosurgery, Vol 5, No 1 (March), 2002: pp 25-49 2 5
Fig 1. Extrinsic intermittent compression of the left VA. Os- teophytic spurs (arrow heads) compress the VA during head rotation to the right,
Fig 2. (A) Lateral and (B) anterposterior angiographic views showing extrinsic intermittent compression of the left VA by fibrous bands (arrows) during extension of the head and neck. The VA enters the transverse canal at C5. (C) Operative view showing the C5 transverse process (between the for- ceps and the number 5) has been resected. Notice the bay- onet-shaped course of the VA (asterisks),
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i~ A
Fig 3. (A) Early and (B) late phase anteroposterior angiograms showing extrinsic compression of the origin of the left VA by a sympathetic element crossing its anterior aspect. In the late phase, the contrast media stagnates in the first few centimeters of the VA. The arrows indicate the VA just beyond compression. (C) Operative photograph of the same case before the sympathetic element (black star) compressing the anterior aspect of the VA (open star) is divided. (D) Operative photograph after release of the compression. Subclavian artery (black circle). (Reproduced with permission from: The Vertebral Artery: Pathology and Surgery. B. George, C. Laurian. Springer-Verlag. Wien and New York. 1987. p 258)
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 2 7
Fig 4. Schematic diagram in the axial plane showing the possible extensions of a foraminal neurinoma. A, Intradural and extramedullary (M = Spinal cord); B, Intraspinal and extradural; and C, Extraspinal. (Reproduced with permission from: The Vertebral Artery: Pathology and Surgery. B. George, C. Laurian. Springer-Verlag. Wien and New York. 1987. p 258)
toward the dura or even into the intradural space and laterally toward the soft tissues of the neck. Hourglass neurinomas therefore may have an extraspinal component, an intraforami- nal component, and an intradural component. Depending on the origin of the neurinoma, the VA is most often displaced anteriorly and medially (Figs 5 and 6). Sometimes, however, the VA is pushed medially inside the foramen (Fig 7).
Other types of neuromeningeal tumors may have an intrafo- raminal component, but they are much less common than neurinomas: meningiomas, paragangliomas, and hemangio- blastomas (Fig 8). The features of hemangioblastomas and paragangliomas are similar to those of neurinomas except the vascularization of the former is greater. Like any extradural meningiomas, foraminal meningiomas harbor invasive features toward the sheaths of the nerves and vessels. Accordingly, the periosteal sheath of the VA is often invaded by these meningi- omas but not the arterial wall itself.
Different tumors originating from the bone or from the soft tissues (Table 2) also can contact or encase the VA 7 (Fig 9). Chordomas, osteoid osteomas, plasmocytomas, sarcomas, and aneurysmal cysts are among the most common.
Surgical Technique:
V2 Segment. The general principle underlying surgical re- section of a VA compressive lesion is to gain exposure and control the VA proximal and distal to the lesion. 34 The trans- verse foramen superior and inferior to the lesion are opened, and the VA inside the foramen is controlled while preserving the periosteal sheath (Fig 10). Dissection proceeds both inferi- orly and superiorly toward the lesion. At the level of the lesion, the periosteal sheath may be opened by the tumor or creating part of the compression but control of the venous plexus at this stage is not a problem. Packing with surgicel or bipolar coagu- lation easily stops the venous bleeding.
Next, the compressive entity must be resected. The ease of
decompression depends on the lesion. When the compression is intermittent, the goal is to decompress the VA rather than to resect the lesion. Therefore, mobilizing the VA is sufficient. To do so separates the compressive element from the VA and most often requires partial resection (Fig 3). Separating the compres- sive element from the VA can be easy task in case of fibrous bands. Conversely, it is often difficult if osteophytic spurs are the cause of compression because the periosteal sheath typi- cally is involved in the degenerative bony process.
In case of permanent compression, which usually implies a tumor, the goal is to resect the lesion as radically as possible. The VA is controlled to divide the vascular supply of the tumor and to separate the VA from it. Afterward, the tumor can be resected safely (Figs 11 and 12). In the case of neuromeningeal tumors, the nerve root is involved and must be exposed distal to the tumor (ie, lateral to the VA, Fig 10).
The nerve root runs an oblique course from superiorly and medially to inferiorly and laterally. It crosses the posterior as- pect of the VA between two transverse processes and the tip of the lower transverse process. The best place to expose a nerve root is at the tip of the transverse process. The longus capitis muscle that covers the lateral part of the transverse process is divided. The tip of the transverse process is controlled by iden- tifying the attached tendons of the scalenus muscle. The nerve root runs between two digits of the scalenus muscle (Fig 19D). A tendon of the scalenus muscle must not be confused with a nerve root: they took similar and course in the same oblique direction.
Dissection proceeds along the nerve root, progressing medi- ally toward the VA (Fig 10B). It is possible but not always easy to separate the periosteal sheath of the VA from the nerve root sheath because they usually adhere to each other, especially in the case of tumor. Consequently, attempting such separation may tear the VA periosteal sheath.
Dissection progresses behind and medial to the VA into the intervertebral foramen. If the tumor extends further medially into the spinal canal, it can be followed to the dura mater by taking advantage of the enlargement of the foramen by the tumor (Fig 10C). The foramen can be enlarged further, as required, by drilling the posterolateral corner of the adjacent vertebral bodies. The intraspinal and even an intradural exten- sion of the tumor can be resected. In the latter case, the extra- dural part is debulked first. Next, the dura mater is incised a few millimeters on both sides of the nerve root, and the intradural portion of the tumor is extracted (Figs 10, 13-15).
Tumors located at the upper part of V2 (at C2-C3) raise particular problems (Fig 13). Proximal control is gained at C3-C4 without technical difficulties. Conversely, distal control of the VA must be obtained at V3 between the C1 and C2 transverse processes. At this level the accessory nerve crosses the surgical field and must be identified and controlled (see The Surgical Exposure of the VA). Between C3 and C2, the course of the VA is complex and turns a corner at the lateral base of the C2 vertebral body. From this corner, the VA runs horizontally toward the C2 transverse process, which is longer and more oblique than the lower (C3, C4, C5 and C6) transverse pro- cesses (Fig 13). Therefore, this portion of C2-C3 must be ex- posed carefully, working alternatively superiorly (at C1-C2) and inferiorly (at C3-C4).
VI Segment. Intermittent compression at V1 is exceptional. We have treated only one such case in which a sympathetic
28 GEORGE, ALVES, AND CARPENTIER
Fig 5. (A) Axial CT scan of an hourglass neurinoma (arrow heads) with a small intraspinal-extradural extension displacing the VA anteriorly and medially as shown in B and C. (B) Lateral angiographic view showing anterior displacement with compression of the VA (arrow head). (C) Anteroposterior angiographic view showing medial displacement with compression of the VA (arrow head).
Fig 6. Anteroposterior angiography view showing lateral dis- placement and severe compression of the VA (arrows) by a chordoma surrounding the vessel at C3-C4 level.
mor from extending to the VA wall. When the VA is encased by a tumor, it is prudent to perform a balloon occlusion test (Fig 16). If the- patient fails to tolerate the balloon occlusion, a bypass must be considered. 37-4o Of 114 lesions involving V1 and V2, we have had to occlude the VA in only two cases. A bypass with a venous graft was necessary between the common carotid artery and the distal VA. In a &year-old boy, both VAs were encased by an osteoblastoma. Both VAs had to be oc- cluded and revascularization was necessary to embolize the tumor bilaterally before surgical resection. In the other patient, a chordoma surrounded the dominant VA (Fig 17). In the same stage, a carotid artery-to-vertebral artery bypass was performed before the tumor, including the VA, was resected. A third by- pass between the common carotid artery and the distal VA was performed in a patient with a fibrous band that almost com- pletely occluded the VA and could not be reopened by simple decompression.
In two patients with neurinomas, the VA was inadvertently torn during separation of the VA from the tumor. The tears were small and might have corresponded to rupture of the origin of a VA branch. The tears were repaired by stitches with temporary clipping of the VA.
Another issue that must be assessed carefully before surgery at V2 is the absence of an anterior radiculomedullary artery arising from the ipsilateral VA at or near the tumor (Fig 16). In such cases, the VA must be left in the transverse canal to avoid stretching the vessel. If the radiculomedullary artery originates exactly at the level of the tumor, which has never happened in our experience, every attempt must be made to save the vessel. It is probably best to leave the capsule or a thin layer of tumor on the vessel side.
element compressed the VA a few millimeters from its origin (Fig 3).
Permanent compression is also unusual because the VA runs freely in the soft tissues. Therefore, the VA may be displaced markedly but is rarely stenosed by a compressive factor. If V1 is stenosed by compression, it will be at the entrance of VA into the C6 transverse foramen where the artery is fixed to the per iosteum (Fig 14A). Causes of perma- nent compression at V1 are the same as those observed at V2. Tumors, especially neurinomas, are the most common (Figs 14 and 15).
As at V2, gaining proximal and distal control is the underly- ing surgical principle. Distal control often requires exposing and opening the C6 transverse process. Proximal control may require exposure of the subcalvian artery. Separating the VA from the tumor seldom is difficult because there is no periosteal sheath at this level and no contact between the VA and the nerve roots or bone. Consequently, the tumor capsule rarely adheres to the VA wall. Compared to the surgical exposure at V2, however, the operative field at V1 is deeper and more narrow.
Problems With the VA
There are seldom problems with the VA. Even if a malignant tumor encases the VA, the adventitia is almost never invaded. The periosteal sheath is resistant barrier that prevents the tu-
Fig 7. Axial CT view of an hourglass neurinoma displacing the VA medially inside the foramen. The VA is indicated by a balloon (arrow) placed inside the VA to perform an occlusion test,
30 GEORGE, ALVES, AND CARPENTIER
Fig 8. (A) Axial MRI and (B) anteroposterior angiogram showing an hourglass hemangioblastoma at C5-C6.
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 31
Fig 9. (A) Preoperative axial CT showing an osteochondroma at C4-C5. (B) Postoperative axial CT shows that minimal bone was resected.
32 GEORGE, ALVES, AND CARPENTIER
13
r
Fig 10. Schematic drawings showing the principles underlying surgical resection of an hourglass neurinoma at V2. (A) Surgical exposure of the lateral aspect of the vertebral bodies and transverse processes (P). The VA (V) is controlled proximal and distal to the tumor (T) by opening the transverse foramen. The distal nerve root (N) is exposed between the tendon of the scalenus muscles (S) at the t ip of the transverse processes. (B) The distal nerve root (N) has been divided and the tumor (T) lateral to the VA (V) has been resected. (C) The medial part of the tumor, including the intradural portion has been resected after the posterolateral corner of the vertebral bodies is dril led and the dura mater (D) is incised. V = VA. N --- Cervical nerve root.
Fig 11. Operative photographs of a foraminal neurinoma before (A) and after (B) its removal. T = Tumor. Black star = VA. S = Sympathetic chain. The numbers 4, 5 and 6 indicate the lateral aspect of the C4, C5 and C6 vertebral bodies.
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Fig 12. (A) Preoperative and (B) postoperative axial CT scans of an aneurysmal cyst involving the lateral part of the C4 and C5 vertebrae (cont'd).
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 3 5
Fig 12. (Cont'd). Corresponding (C) preoperative and (D) postoperative surgical views. T = Tumor. Black star = VA. N = Nerve root.
3 6 GEORGE, ALVES, AND CARPENTIER
Fig 13. Hourglass neurinoma at C2-C3 with extraspinal, intraforaminal, intraspinal-extradural, and intradural-ex- tramedullary components. (A) Axial, (B) coronal (at the spinal cord level), and (C) coronal (at the vertebral bodies level) MRIs before surgical resection. T = Tumor. Arrows = VA. (D) Coronal CT scans showing the extent that the vertebral bodies have been drilled. Arrow heads = VA.
t
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 3 7
Fig 13. (Continued). (E) IntraoperaUve view (left side) after tumoral resection. 1,2, 3 indicate the VA at C l -C2, C2-C3 and C3-C4, respectively. The tip of the spatula is at the t ip of the transverse process of C2. D -- Opened dura mater.
TABLE 2. Types of Tumors Causing Permanent Compression of V l and V2 in 114 Casest
Fig 14. Hourglass neurinoma at C6-C7 level wi th extraspinal, intraforaminal, intraspinal-extradural, and intradural-ex- tramedul lary components. (A) Sagittal and (B) axial MRIs before surgical resection. T = Tumor. Ar row heads = VA. (C) Axial CT scan after surgical resection. Intraoperative views (right side) (D) before and (E) after the tumor has been resected. In E, the blade is no longer retracting the jugular vein and the VA cannot be seen. Black star = VA. N = Nerve roots. P = Phrenic nerve. Black circle = Internal jugular vein. Open circle = Subclavian artery.
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 3 9
Fig 15. Extradural meningioma developed from the C8 nerve root. Axial CT scans (A) before and (B) after surgical resection. T = Tumor. Intraoperative views (left side) showing the different steps of surgical resection. (C): The tumor (T) is exposed by opening the field between the internal jugular vein (black circle) and the sterno-mastoid muscle (M) detached from the clavicle and the sternum. The sympathetic chain (S) and two nerve roots (5 and 6) are visible. (D) The lateral part of the tumor (T) has been debulked and is pushed down to expose the VA (black star). (E) The VA (black star) has been controlled after the C6 transverse process is opened. The C5, C6, C7 and C8 nerve roots (5, 6, 7, and 8) are visible. The C8 nerve root is thickened by tumoral infiltration. (F) The tumor, including the foraminal part has been removed completely after limited drilling of the posterolateral corner of the vertebral body and division of the C8 nerve root distal and proximal to the tumor.
4 0 GEORGE, ALVES, AND CARPENTIER
Fig 16, Undifferentiated sarcoma at C5-C6-C7, Axial CT scans at C5 (top left) and C7 (bottom left). Angiograms before (middle) and during a balloon (delineated by dots) occlusion test (far right). Notice the stenosis of the VA, the small tumoral injection from the C5 radicular branch, and the anterior radiculomedullary artery arising from the C6 radicular branch (arrow heads),
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 41
Fig 17. (A) Sagittal and (B) Coronal MRIs showing a chor- doma involving the C2-C3 and C4 vertebrae. (C) Postopera- tive angiogram showing a saphenous vein graft by-pass (arrows) between the common carotid artery and the distal VA, From C2 to C5 has been fixated with bone grafting and plating.
42 GEORGE, ALVES, AND CARPENTIER
Problems With the Nerve Root
It is always possible to dissect the nerve root, separating it from the VA along its course into the foramen and down to its junction with the dural sac (Fig 19D). Troublesome venous bleeding can occur from the foramen venous plexus when the tumor is debulked. Coagulation is better than packing with surgicel. If the tumor involves the nerve root (eg, neurinoma, meningioma), preservation of the nerve root is questionable. 34 In about 90% of neurinomas, the nerve root can be divided without adverse consequences. To assess the feasability of this option, the nerve root is stimulated distal to the tumor. If no motor response is obtained, the nerve root can be sacrificed. Otherwise, it must be preserved either by resecting the tumor if it can be separated from the nerve fascicles or by performing a subtotal resection.
Other Causes of Morbidity
Causes of morbidity are limited to problems with the sympa- thetic chain and lymphatic vessels. The sympathetic chain must be indentified under the aponeurosis of the longus colli muscle and gently retracted with the aponeurosis. Typically, this re- traction is best achieved laterally, which preserves the rami communicantes connecting the sympathetic chain with the nerve roots. In some cases, however, medial retraction is the best choice because of the natural position of the sympathetic chain and the absence of rami communicantes. With hourglass tumors extending laterally beyond the tip of the transverse processes, lateral retraction would place the sympathetic chain at risk of injury. Preservation of the main trunk of the sympa- thetic chain avoids Horner's syndrome. However, even very gentle manipulation and division of the rami communicantes
\
Fig 18. General principle of the oblique corpectomy tech- nique. The VA is controlled in the transverse canal but left in place, The posterolateral corner of the vertebral bodies is drilled off (dotted lines),
can lead to a transient Horner's syndrome that lasts from a few days to 2 months. Overall in our series the rate of definitive Horner's syndrome for any type of surgery around the VA is 3%.
Regardless of their size, the lymphatic vessels at V1 must be identified and ligated. Slight oozing without visible damage to the lymphatic vessels can be treated by packing the area with Surgicel stuck with fibrin glue. Lack of control of the lymphatic vessels can cause lymph to ooze through the skin incision and requires reopening the wound.
Oblique Corpectomy for Anterior and Lateral Lesions of The Cervical Spine
In an oblique corpectomy, the posterolateral corner of the cer- vical vertebral bodies is drilled obliquely to reach the anterior part of the spinal canal (Figs 18-20). The bone drilling starts from the lateral side of the vertebral bodies just above the transverse canal, which therefore must be exposed. This tech- nique permits access to small bone lesions in the vertebral bodies or pedicles, lesions in the extradural space anterior to the dural sac, intradural lesions, and even intramedullary le- sions. Its main advantage compared to other techniques is less bone drilling, which eliminates the need for reconstruction or osteosynthesis in many cases. 41,42 Moreover, it provides wide access to the intervertebral foramen, which permits exposure of the cervical nerve root from its junction with the dural sac to the brachial plexus (Figs 19 C and D).
Surgical technique
An oblique corpectomy may be applied to any part of the cer- vical spine but is most often used at V2. The first step is to expose the VA in the transverse canal through an anterolateral approach (see Surgical Exposure of the VA). The VA is left in place, but its anterior and medial aspects must be controlled. Therefore, the drilling starts as close as possible to the VA but a piece of bone is left between the VA and the drill to protect the artery (Fig 19 A). The bone drilling starts on the lateral side of the vertebral bodies just above the VA and the transverse pro- cesses. The drilling must be directed as vertically as possible toward the cortical bone of the posterior aspect of the vertebral bodies. Once the cortical bone is reached, the drilling is ex- tended contralaterally following the cortical bone to minimize the extent of bone resection.
There is no perfect method to determine the extent of drilling
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 4 3
, . , r
Fig 19. Cadaveric views of an oblique corpectomy. (A). The VA (black star) has been control led by opening a transverse process. The Iongus colli muscle (C) has been cut. The internal jugular vein (black circle) is retracted by the blade. The lateral aspect of the vertebral body has been drilled down to the cortical bone (astericks), The bony wall (open star) medial to the VA has been preserved to protect the VA during drilling. (B) The drilling has been completed and the posterior longitudinal l igament held by the forceps has been resected showing the dura mater ([3). Black star = VA. (C) The bony wall medial to the VA has been removed so that the cervical nerve root (astericks) can be shown, The VA (black star) has been separated from the cervical nerve root and is retracted by a spatula. (D) The Iongus capitis muscle (C) has been divided to expose the cervical nerve roots (asterick). The tendon of the scalenus muscle (T) is between the nerve roots. Notice the VA (black star). (E) Intraoperative view corresponding to the view shown in A. Black star = VA. C = Longus colli muscle. Black circle = Internal jugular vein. Asterisk = Posterior longitudinal ligament,
4 4 GEORGE, ALVES, AND CARPENTIER
tion. This situation is typical of spondylotic myelopathy for which the spinal cord may need to be decompressed at as many as 5 levels. Similarly, when an oblique corpectomy involves only one intact disc and two adjacent vertebral bodies, the stability is uncompromised. If, however, the drilling includes the opening of the intervertebral foramen, it is safe to place a bone graft. When an oblique corpectomy involves several levels with intact discs, bone grafting and osteosynthesis are neces- sary to prevent postoperative kyphosis.
An iliac bone graft, impacted between the vertebral bodies, is used in most cases. The bone graft must be placed approxi- mately horizontal with a plane of cortical bone parallel to the posterior ligament (Figs 17 and 23).
Fig 20. Coronal CT scan after an oblique corpectomy at C3-C4 and C4-C5 showing the bone window through which the vertebral bodies have been drilled (arrows).
on the posterior aspect of the vertebral bodies and therefore to ascertain that the planned point has been reached. Neuronavi- gation can be used to check the position of an instrument tip. The simplest method is to measure the distance between the medial aspect of the VA and the target point on the posterior aspect of the vertebral body on preoperative CT. Intraopera- tively, the same measurement is repeated using a needle with a millimetric scale. The cortical bone should be kept intact until the desired point is reached to avoid the dural sac from bulging into the field and impairing visibility of the distal part of the bone yet to be drilled.
Once the target point is reached, the cortical bone is re- sected with a d iamond drill from the distal to the proximal part. The posterior longitudinal l igament covering the dural sac becomes visible (Fig 19B). On the ipsilateral side of the approach bone remains between the drilled port ion and the VA. If the drilling was proceeded obliquely, the remaining corner of bone may be rather large. The oblique corpectomy can be extended as far as the opposite pedicle. On the side of the surgical approach, the bone medial to the VA can be ,resected down to the pedicle to open the intervertebral fora- meh completely. (Fig 19C).
Stability
In general the spine remains stable as long as it was stable before surgery and the discs were collapsed on preoperative examina-
Indications
Spondylotic myelopathy and radiculopathy 43. The most fre- quent and the best indication for an oblique corpectomy is spondylotic myelopathy (Figs 21 and 22, Table 3). The criteria for this technique are similar to those of the anterior corpec- tomy technique: a predominance of anterior compressive ele- ments and a straight or kyphotic cervical axis. An oblique cor- pectomy has two advantages. In almost all cases, it avoids the need for stabilization. If radiculopathy is present, it offers the best lateral decompression at the intervertebral foramen. De- compression can be performed on as many levels as necessary (as many as five levels). If radiculopathy is caused by foraminal stenosis, decompression can be restricted to the intervertebral foramen with limited bone drilling. This technique of foraminal enlargement is similar to the one used for hourglass tumors.
Hourglass tumors. If hourglass tumors extend through the intervertebral foramen into the spinal canal and even into the intradural space, 34,3~ the intervertebral foramen can be en- larged by drilling the posterolateral corner of the vertebral bodies. After the extradural part of the tumor is debulked, the dura mater is incised a few millimeters on both sides of the nerve root and the intradural portion of tumor extracted (Figs. 10, 13-15). 34
Bone tumors. Small bone tumors like osteoid osteomas may be located in the posterolateral corner of the vertebral body or in the pedicle adjacent to the transverse canal. A limited oblique corpectomy provides direct access to the lesion without exten- sive bone drilling or destruction of the facet joint. Conse- quently, a fusion procedure can be avoided.
In large tumors the lateral approach permits any part of the tumor, including the lateral aspect near the transverse canal, to be reached (Figs 12 and 23).
Intramedullary lesion. An intramedullary lesion is excep- tional indication for spinal cord lesions located and protruding anteriorly. In this case, a standard posterior approach is inade- quate because it would be necessary to go through the entire spinal cord. If the lesion reaches the anterior surface, an ante- rior route is preferable. In our series one anterior cavernous angioma was removed through an oblique corpectomy that involved one disc space and most of the two adjacent vertebral bodies. An iliac bone graft was placed at the end of surgery. The cruciform incision of the dura mater could be closed tightly, and the prepared flap of the posterior longitudinal ligament was replaced over the dura.
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 4 5
Fig 21. Spondylotic myelopathy treated by oblique corpectomy at C4-C5 and C5-C6. Axial CT scans (A) before and (B) after surgical decompression. Sagittal MRIs (C) before and (D) after surgical decompression. The numbers 4, 5 and 6 indicate the C4, C5, and C6 vertebral bodies, respectively. (Reproduced with permission from: B. George. My(Hopathie cervicarthrosique. Encycl Med Chir, 1998)
4 6 GEORGE, ALVES, AND CARPENTIER
Fig 22. (A) Sagittal MRIs showing an oblique corpectomy decompression at 4 levels (C3 to C7) performed for the treatment of spondylotic myelopathy. (B) Axial CT scans showing the extent of bone resection. Notice the VA in the transverse foramen (arrow),
UPPER CERVICAL VERTEBRAL ARTERY SURGERY 4 7
L ~
Fig 23. (A) Coronal and (B) axial MRIs showing a chordoma (T) at C4-C5 encasing the VA (arrows). (C) Postoperative axial CT scan after surgical resection of the tumor, Notice the iliac bone graft and the plate (asterick). (D) Intraoperative photograph showing that the tumor medial to the VA has been removed through an oblique corpectomy. (E) The VA is mobil ized laterally, and the lateral part of the tumor involving the nerve root has been resected down the to sPinal cord. Notice the dural opening (arrow heads). Black star = VA. Asterisks = Nerve roots.
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