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Stabilization of the Craniocervical Junction Following Resection of Chordomas and Chondrosarcomas of the Skull Base and Spine
© 2018 Elsevier Inc. All rights reserved. Please note that the copyright for the original figures submitted by the contributors is owned by Contributors.
Introduction
Tumors involving the skull base demonstrate diverse histology and distinct clinical implications, including chordomas and chondrosarcomas. Advances in operative techniques enable resection of these tumors. The underlying pathology and tumor growth, as well as the extent of bony resection during surgery, may produce significant instability of the craniocervical junction (CCJ). The anatomic relationships that comprise the CCJ are unique. Bony resection may produce both acute and long-term implications for atlanto-occipital stability.
Biomechanical studies have demonstrated that the extent of condylar resection directly influences CCJ stability. The bony and ligamentous structures of the CCJ provide stability, and the articulations enable a broad range of motion, accounting for 25% of neck flexion–extension and 40 degrees of head rotation. This substantial amount of motion both explains the propensity of this spinal segment to develop pseudoarthrosis when a fusion attempt is made and illustrates the significant change in cervical range of motion produced in an occipitocervical fusion. Each of these factors should be weighed in operative decision making.
Instability of the CCJ can lead to marked pathological translation, longitudinal displacement, and/or basilar invagination. Occipitocervical stabilization may be required when pathological instability occurs secondary to tumor invasion or develops secondary to treatment. Clinical and cadaveric studies have established that more than 50% resection of the condyle promotes hypermobility at the occipitoatlantal junction.
The primary goals of stabilization include preservation of alignment, encouragement of arthrodesis, and an expedited return to daily activities with minimal postoperative immobilization. Instability of the CCJ is addressed primarily via posterior surgical approach and may include the placement of instrumentation, allograft/autograft, and other stabilization techniques.
Surgical Technique
Early approaches to posterior stabilization involved subperiosteal dissection, followed by the onlay of autograft to encourage fusion of the targeted spinal levels. Rates of pseudoarthrosis, especially at the CCJ, prompted improvement in operative techniques. A variety of techniques, such as the use of iliac crest struts, methylmethacrylate, or allograft rib, have been described. Instrumentation, such as plates, loops, and rods, may immediately stabilize the CCJ and may improve the rates of fusion at this highly mobile spinal segment.
Preoperative Decision Making
Stabilizing the CCJ is often accomplished through a posterior approach. Anterior approaches have been reported, but may pose higher complication rates. Next, we detail a posterior approach for stabilization of the CCJ.
The decision to perform CCJ fusion depends on the degree of junction stability, which is often determined by either the location and size of the surgical lesion or the extent of planned surgical resection. When the degree of bony destruction/resection of the occipital condyles or the degree of bony replacement at the skull base threatens the structural stability at the CCJ, operative stabilization may be necessary.
CCJ fusion may be performed prior, during, or after the surgical resection of a skull base tumor. If fusion is not performed prior to resection, patients are often placed in a halo for external immobilization, pending the stabilization stage of treatment.
Anesthesia Concerns
Patients with CCJ instability may require fiber-optic intubation. Similarly, previous operative approaches in the CCJ may complicate airway management. These concerns should be discussed with the anesthesia team. The operative technique will begin with the administration of a general anesthetic in the supine patient. We routinely use neuromonitoring in this patient population. From the time of anesthesia onward, somatosensory evoked potentials (SSEPs), brainstem auditory evoked potentials (BAEPs), and motor evoked potentials (MEPs) are collected. Preoperative baseline measurements of these parameters are used as a reference to compare the subsequent changes. Baseline neurophysiological recordings are obtained prior to patient positioning.
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