Brief Overview of Surgical Approaches to the Craniovertebral Junction
Section III of Surgery of the Craniovertebral Junction addresses the surgical approaches that are available for exposing lesions at the craniovertebral junction (CVJ). The next several chapters are devoted to these surgical approaches, attesting to their variety and the difficulty in selecting the optimal approach. This overview introduces the surgical approaches and provides a brief discussion of the surgical decision-making process. Approaches to lesions of the CVJ traverse anatomical regions that are the domains of several surgical subspecialties (neurosurgery, otolaryngology, and plastic/craniofacial surgery), and a multidisciplinary skull base team is therefore mandatory.
The surgical approach is selected to maximize operative exposure and to minimize the associated rate of morbidity. First, the surgeon must determine how much exposure is needed. The specific pathology and size of the lesion are important factors in this determination. For example, a small cavernous malformation in a cerebellar peduncle might be removed completely through the limited exposure of a retrolabyrinthine approach, but a large petroclival meningioma might require the extensive exposure of a combined supratentorial and infratentorial approach. Second, the surgeon must determine from which direction to approach a lesion ( Fig. 19.1 ). When the skull base is considered in the axial plane, the CVJ can be approached from three directions: anteriorly, laterally, and posteriorly. Similarly, when the skull base is considered in the sagittal plane, the CVJ can be approached from three directions: superiorly (transcranial), inferiorly (transcervical), and with a combination of both ( Fig. 19.2 ). The location of the lesion and the adjacent anatomy are critical factors in selecting the best angle of approach. In the past decade stereotactic methods of localization have been refined and are invaluable in minimizing surgical morbidity while pinpointing the location of a lesion. These methods are discussed in Chapter 20.
Anterosuperior approaches to the CVJ consist of the transoral (Chapter 21), transoral–transmaxillary (Chapter 22), transoral–translabiomandibular (Chapter 23), and transfacial approaches, which include the transpalatal and transfrontalnasal-orbital approaches (Chapter 24). Minimally invasive approaches include endoscopic approaches, which may diminish the need for high morbidity exposures (Chapters 25 and 26). The transoral and transfacial approaches are best suited for extradural midline lesions. Attacking intradural pathology through one of these approaches risks contamination with nasopharyngeal organisms, meningitis, and cerebrospinal fluid (CSF) leaks. Consequently, midline intradural lesions are better treated through a lateral approach (i.e., one of the transpetrosal approaches or a far lateral approach). For extradural pathology, the upward extension of a lesion from the CVJ determines which of these transoral or transfacial approaches to select. Lesions on the inferior clivus can be accessed with a transoral, transpalatal, or transmaxillary approach. Lesions with further upward extension might require a transnasomaxillary approach or, if the middle and anterior cranial fossae are involved, one of the transfrontalnasal orbital approaches. Midline lesions that extend inferiorly from the CVJ and that cannot be exposed fully with one of the transoral approaches may require the additional exposure provided by osteotomies of the mandibular rami bilaterally or by a midline exposure, splitting the tongue and mandible. Lesions that extend inferiorly from the CVJ and off midline might best be exposed through a retropharyngeal or mandibular swing approach.
The lateral approaches to the CVJ consist of the retrosigmoid approach (Chapter 33) and the presigmoid/transpetrosal approaches (Chapter 28). The extended transpetrosal approaches combine a petrosectomy with the standard neurosurgical approaches to increase exposure. For example, a petrosectomy combined with a subtemporal craniotomy adds a supratentorial exposure for lesions that extend superiorly. Similarly, a petrosectomy combined with a far-lateral craniotomy adds exposure of the foramen magnum for lesions that extend inferiorly. These approaches are most appropriate for laterally placed intradural lesions, but extensive bone removal through the transpetrosal approaches can provide access to midline lesions (e.g., aneurysms, chordomas, and meningiomas). These lateral approaches are preferred over anterior approaches for intradural lesions because they avoid the contaminated spaces in the nasopharynx and optimize dural repair, thus minimizing the risk of CSF leakage in the postoperative period.
Because some degree of petrosectomy is required for lateral approaches, the surgeon must estimate the amount of temporal bone resection needed to obtain adequate exposure. This evaluation is balanced with an assessment of the patient′s preoperative neurological function—specifically, the function of cranial nerves VII and VIII. When hearing preservation is a goal, temporal bone removal is limited to retrolabyrinthine drilling. However, the exposure is then limited to the cerebellopontine angle. When patients have poor hearing before surgery, translabyrinthine drilling increases exposure to the anterolateral brainstem at the expense of hearing. When large lesions compress the brainstem and produce hearing loss and facial nerve deficits before surgery, transcochlear drilling, which transposes the facial nerve at the expense of transient deficits, is ideal. However, the increase in surgical exposure of the cranial base is traded for increased surgical morbidity, leading to an emphasis on careful selection of aggressive transpetrosal approaches based on these factors. In particular when applied to the management of benign tumors, such as meningiomas, the addition of stereotactic radiosurgical management (Section II, Chapter 18) has affected our treatment algorithm, and the use of transcochlear exposures in such cases has declined significantly.1,2 With the development of endovascular techniques over the past decade (Chapter 30), treatment of vascular lesions has evolved. Nevertheless, such approaches remain necessary and helpful and should be part of the armamentarium of the experienced skull base surgeon. Examples of approach selection for upper cervical spine pathology are presented in Chapter 29, whereas those for upper cervical vertebral artery pathology are reviewed in Chapter 31.
Posterior approaches to the CVJ consist of the suboccipital approach (Chapter 33) and the far-lateral approach (Chapter 27). Determining which of these two approaches to use depends on whether an inferior exposure is needed below the level of the internal auditory canal and pontine structures to view the distal vertebral artery and inferior clivus. The far lateral approach provides such additional lateral and inferior exposure; the standard suboccipital approach is adequate for higher and more midline lesions. These two approaches are remarkably versatile and are used to treat a variety of posterior and posterolateral lesions at the CVJ that are discussed in Section II Chapters 12, 15, and 16, including Chiari malformations (Chapter 12), cerebellar and brainstem vascular malformations (Chapter 15), vertebral and vertebrobasilar artery aneurysms (Chapter 16), and jugular foramen tumors (Chapter 32).
References
1. Bambakidis NC, Kakarla UK, Kim LJ, et al. Evolution of surgical approaches in the treatment of petroclival meningiomas: a retrospective review. Neurosurgery 2007;61(5, Suppl 2):202–209, discussion 209–211 2. Bambakidis NC, Safavi-Abbasi S, Spetzler RF. Combined surgical approaches. In: Bambakidis NC, Megerian CA, Spetzler RF, eds. Surgery of the Cerebellopontine Angle. Shelton, CT: BC Decker/PMPH; 2009Related posts:
Posterior Neuroendoscopic Applications at the Craniovertebral Junction
Approaches to the Jugular Foramen
Transoral–Translabiomandibular Approach to the Craniovertebral Junction
Transfacial Approaches to the Craniovertebral Junction
Bypass Options for the Posterior Fossa
Suboccipital and Retrosigmoid Approaches
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