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Intraoperative neuronavigation for transoral surgical approach: use of frameless stereotaxy with 3D rotational C-arm for image acquisition.

Introduction

Accessing the craniovertebral junction via the transoral approach was first described in 1935 by German and since then has been further refined by many surgeons. (1-4,6-8) Two main concerns with this approach center on the morbidity of a pharyngeal incision to access the central nervous system, and the danger to underlying structures such as the brainstem. Neuronavigation, the use of a computer-assisted spacial coordinate system to identify anatomy based upon radiographic imaging, is a standard adjunct to cranial surgery (5) and can improve safety in the transoral approach by minimizing the pharyngeal opening and by aiding to orient the surgeon; however, this technique generally depends upon fixation of the skull relative to known points, thus neuronavigation-assisted surgery in the cervical region remains difficult secondary to the mobility of the cervical spine in relation to the cranium. Previously described methods utilize preoperative application of a halo fixation device (10) or custom oral occlusal splints (11) for intraoperative navigation. The use of intraoperative MRI has also been advised to assess the degree of surgical decompression. We describe the use of BrainLab VectorVision neuronavigation with intraoperative 3D C-arm image acquisition to improve the safety of the transoral approach.

Patient 1

A 67 year old female presented with a chief complaint of neck pain, but upon further questioning also admitted to dysphagia, intermittent numbness and weakness in the hands bilaterally, and positional disequilibrium with multiple prior falls. She was noted to have bilateral clonus, 3+ muscle stretch reflexes throughout, and loss of gag reflex. On magnetic resonance imaging (MRI) of the cervical spine she was noted to have a large reactive lesion at the C1-C2 junction causing brainstem compression.

Surgical decompression was recommended because of her neurologic symptoms and brainstem compression. Surgical positioning was accomplished using a radiolucent Mayfield clamp with 3-point pin fixation. The Siemens Iso-3D rotational C-arm was used to obtain a stereotactic data set (Figure 1). A standard transoral approach for transodontoid resection of this lesion was then accomplished. We performed a partial resection of the dens with a high speed drill and removed the retro-odontoid reactive tissue with curettes and rongeurs to achieve excellent decompression of the brainstem. Neuronavigation was used throughout the surgery to plan the surgical approach and define margins of the resection. Postoperatively she had no new deficits, tolerated a diet, and was discharged to an acute rehab facility to maximize her rehabilitation from her pre-existing neurologic deficits. At six month follow-up she had no gait disturbance, resolution of clonus, normalization of reflexes, and complete resolution of her pain symptoms.

Patient 2

A 57 year old female with previous breast cancer presented with a one year history of progressive headaches, right-sided tongue deviation, and vague sensory complaints. MRI demonstrated a predominantly right-sided mass at C1 and C2, behind the odontoid, hyperintense on T2 weighted imaging, and compressing the upper cervical spinal cord. Physical examination confirmed a right hypoglossal nerve palsy but other cranial nerves were intact and there were no signs of myelopathy. The MRI characteristics were consistent with a synovial cyst. Decompression through a transoral approach was recommended due to her neurologic symptoms and as confirmation of a non-malignant process.

[FIGURE 1 OMITTED]

For the operative intervention, the patient was placed in a radiolucent Mayfield clamp with 3-point pin fixation to immobilize the craniovertebral junction. A Siemens Iso-3D C-arm coupled to a neuronavigation system was used to acquire a 3-dimensional dataset of the bony anatomy. The neuronavigation was then used in the surgical approach to identify the optimal area and size of the pharyngeal incision. A vertical 3 cm incision was made along the posterior pharyngeal wall and the periosteum of the dens was stripped in the direction of the lesion (Figure 2). Partial odontoid resection was then carried out, along with decompression of the cyst and resection of anterior portion of the cyst wall. The anterior arch of C1 as well as the contralateral two-thirds of the odontoid process were left intact to aid in postoperative stability. The dura was visible beneath the decompressed lesion. The patient remained neurologically intact after surgery except for her previous right 12th nerve palsy. Her diet was advanced and her post operative course was uneventful. Pathology confirmed synovial cyst, and follow-up MRI ten weeks after surgery demonstrated complete resection of the lesion.

[FIGURE 2 OMITTED]

Discussion

The transoral approach represents a direct route to extradural midline pathology from the mid-clivus to the C2/3 disc space; however, its use has been significantly limited by the severe morbidity and mortality of perioperative complications. Potential significant complications of the transoral approach include cerebrospinal fluid (CSF) leak or wound breakdown resulting in potentially fatal infections; spinal cord injury, vertebral artery injury, and post-operative bony instability. However, neuronavigation may mitigate the risk of some of these complications.

Wound breakdown after a transoral approach has a mortality rate approaching 100% in historical studies. The risk of incisional problems is likely related to the length of the pharyngeal incision and the ease of closure, both of which may be improved by neuronavigation, which allows a smaller incision to be placed in an optimal location rather than the classic "U" or "H" shaped pharyngeal incisions which provide a wider exposure but increase the risk of wound problems of the delicate pharyngeal mucosa. More recent studies have advocated the use of a midline vertical incision, which was used in both cases above. Previous publications describe an incision approximately 2 cm superior and 2.5 cm inferior to the anterior tubercle of C1. (1,4) In our experience we were able to limit incision size to approximately 3 cm, as compared to 4-5 cm. Furthermore, although the pharyngeal tubercle is the classic palpable landmark to verify the midline and the level of C1, intraoperative navigation aids in more exact localization of underlying pathology and may be especially helpful in cases where the anterior bony anatomy is altered by the disease process.

An accurate knowledge of the lateral and posterior extent of resection may additionally be accomplished through neuronavigation to aid in avoiding violation of the dura and preventing a CSF leak. This is of particular importance in cases such as chordoma, in which dural invasion may be present and is often unclear from preoperative imaging.

Dural repair through the transoral approach is difficult and CSF leak into the pharyngeal space is a significant complication with high morbidity and mortality, making these key issues in the ultimate success of the surgery. Similarly, injury to the brainstem, upper cervical spinal cord, vertebrobasilar system, eustachian tubes, and hypoglossal nerves may be avoided by accurate determination of the lateral and posterior extent of resection and identification of these critical landmarks.

Finally, the risk of instability requiring fusion after resection of the odontoid and anterior arch of C1 is a concern. The classical transoral approach to pathology behind the odontoid involves resecting the anterior arch of C1 as well as the entire odontoid. More localized removal of bony elements may allow more physiologic load bearing and movement, which may decrease the need for future stabilization. We were able to preserve the anterior arch of C1 as well as approximately half to two-thirds of the uninvolved odontoid. Although we will continue to follow and assess our patients for signs of instability, neither of our patients has required stabilization.

The use of BrainLab VectorVision neuronavigation to aid in surgery at the craniovertebral junction has only been described in basilar invagination, and previously required a preoperative computed tomography scan prior to surgical positioning as image acquisition. (11) This was performed with good reported accuracy of 0.9 and 1.3mm on these respective cases, (11) but neglects the effects of cervical spine rotation or flexion on the bony relationships. Although maintenance of a neutral position in the CT scanner and in the operating room can be attempted, it lacks the precision required for neuronavigation. Previous endeavors to eliminate cervical motion have been described with preoperative halo brace application with good result, but at the cost of both invasiveness and additional operative time. Furthermore, neutral head and neck positioning may not be optimal for the surgical approach, which can be facilitated by extension and lateral translation/ rotation towards the surgeon. Use of an intraoperative 3D C-arm for registration after the patient has been positioned and fixed in place prevents movement of the upper cervical spine without the additional invasiveness of halo application, while allowing optimal positioning rather than being limited to a neutral position. Its use also limits intraoperative radiation after initial data set acquisition, adds minimal time to the operation, and confers valuable intraoperative information.

Conclusion

Neuronavigation in transoral approaches to the anterior craniovertebral junction can improve the safety profile of the procedure. We propose a simple, non-invasive, cost-effective, and accurate method for neuronavigation image acquisition using a 3D rotational C-arm which accounts for motion in the cervical spine and allows the surgeon to optimize positioning.

References

(1.) Apuzzo MLJ, Weiss MH, Heiden, JS, Transoral exposure of the atlantoaxial region, Neurosurgery, 1978; 3, 201-207.

(2.) Blazier CJ, Hadley MN, Spetzler RF, The transoral surgical approach to craniovertebral pathology, J Neuroscience Nursing, 1986; 18, 57-62.

(3.) Delgado TE, Bucheit WA, Surgical management of tumors in and around the clivus via the transoral approach, Contemp Neurosurg, 1982; 4, Lesson 10.

(4.) Greenberg AD, Scoville WB, Davey LM, Transoral decompression of atlantoaxial dislocation due to odontoid hypoplasia: Report of two cases, J Neurosurg, 1968 28, 266-269.

(5.) Gumprecht HK, Widenka DC, Lumenta CP, BrainLab VectorVision Neuronavigation System: technology and clinical experiences in 131 cases, Neurosurgery, 1999; 44, 97-104.

(6.) Hadley MN, Spetzler RF, Sonntag VKH, The transoral approach to the superior cervical spine: A review of 53 cases of extradural cervico-medullary compression, J Neurosurg, 1989; 71, 16-23.

(7.) Menezes AH, Van Gilder JC, Transoraltranspharyngeal approach to the anterior craniocervical junction: Ten years experience with 72 patients, J Neurosurg, 1988; 69, 895-903.

(8.) Spetzler RF, Selman WR, Nash CL Brown, RH, Transoral microsurgical odontoid resection and spinal cord monitoring, Spine, 1979; 4, 506-510.

(9.) Ugur HC, Kahilogullari G, Attar A, Caglar S, Savas A, Egemen N, Neuronavigation assisted transoral-transpharyngeal approach for basilar invagination, Neurol Med Chir, 2006; 46, 306-308.

(10.) Veres R, Bago A, Fedorcsak I, Early experiences with image-guided transoral surgery for the pathologies of the upper cervical spine, Spine, 2001; 26, 1385-1388.

(11.) Vougioukas VI, Hubbe U, Schipper J, Spetzger U, Navigated transoral approach to the cranial base and the craniocervical junction: technical note, Neurosurgery, 2003; 52, 247-250.

Garrett J. Jackson, MD

Department of Neurosurgery, West Virginia University School of Medicine, Morgantown

Cara L. Sedney, MD, MA

Department of Neurosurgery, West Virginia University School of Medicine, Morgantown

Tanya Fancy, MBBS

Department of Otolaryngology, West Virginia University School of Medicine, Morgantown

Charles L. Rosen, MD, PhD

Department of Neurosurgery, West Virginia University School of Medicine, Morgantown

Corresponding Author: Cara L. Sedney, MD, Dept. of Neurosurgery, RCBHSC, PO Box 9183, Morgantown, WV 26506-9183. Email: csedney@hsc.wvu.edu
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Article Details
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Title Annotation:Case Series
Author:Jackson, Garrett J.; Sedney, Cara L.; Fancy, Tanya; Rosen, Charles L.
Publication:West Virginia Medical Journal
Article Type:Clinical report
Geographic Code:1U5WV
Date:May 1, 2015
Words:1820
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