Overview
A variety of surgical approaches have been developed for lesions located at the craniovertebral junction (CVJ). Access to the CVJ can be achieved via anterior, anterolateral, lateral, posterolateral, and posterior approaches depending on the location of the lesion.
The transoral-transpalatopharyngeal approach is most frequently used for anterior midline CVJ lesions because the lower clivus, C1, and C2 will be accessible. Palatal or mandibular splitting may be utilized to achieve further rostral or caudal exposure. One significant disadvantage of the transoral route is its limited lateral visualization. Improved rostral-caudal and lateral visualization can be achieved with the use of angled endoscopes. Despite the use of endoscopes, the transoral approach is typically associated with several complications, including airway and swallowing difficulties, palatal dysfunction, and pharyngeal complications related to the posterior pharyngeal incision. Most of these complications can be avoided with an endoscopic transnasal approach, because the incision will be more rostral, thus avoiding soft palate and pharyngeal complications. If a lesion extends laterally or caudally, the high anterior cervical retropharyngeal approach may be preferable. Another advantage of the high anterior cervical approach is that anterior cervical fixation and fusion can be performed simultaneously from this approach, thus avoiding supplementary posterior fusion.
The far-lateral transcondylar approach (LTA) was first described by Heros. The LTA consists of 1) muscle dissection along the posterolateral CVJ, 2) suboccipital craniectomy or craniotomy with 3) partial removal of the occipital condyle, and 4) partial removal of the posterior arch of the atlas. The LTA is particularly suited to access lesions located in the lower third of the clivus, anterolateral foramen magnum, and anterolateral to the CVJ. The LTA provides a wide lateral exposure to the brainstem while minimizing risk of vascular injury and provides good access to both intradural and extradural lesions, better development of the lesion-brainstem interface, and good reconstruction options for the cranial base. The LTA provides significant advantages over alternative approaches to the anterior aspect of the CVJ. Unlike anterior transoral approaches, no contamination with oral flora occurs with the LTA. In comparison with traditional posterior approaches, the LTA provides better visualization of the vertebral arteries, its branches, and the lateral extent of the lesion with minimal retraction of the brainstem and cerebellum. However, there is a greater risk of lower cranial nerve (CN) deficits, increased incidence of aspiration pneumonia, and more difficulty with dural closure.
Anatomy Review
The CVJ consists of the lower clivus, foramen magnum, and C1–C2 with lateral borders extending to the jugular foramina, hypoglossal canals, and the occipital condyles.
Muscle Layers
Three layers of muscles must be resected to gain the relevant exposure. The most superficial level consists of the sternocleidomastoid (SCM) and trapezius muscles. The middle muscle layer consists of the splenius capitis, longissimus capitis, splenius cervicis, and the semispinalis capitis. The muscles of the deepest layer make up the suboccipital triangle: the rectus capitis is the superior and medial border, the superior oblique is the superior and lateral border, and the inferior oblique is the inferior and lateral border ( Fig. 6-1, D ). The floor of the suboccipital triangle is made up of the posterior arch of the atlas and the posterior atlantooccipital membrane.
Bony Anatomy
The occipital condyles are situated along the anterolateral border of the foramen magnum and project downward (see Fig. 6-1, A ). The longest axis of the condyles is in the anterior-posterior direction with an average length of 21 mm; the articular surfaces are ovoid and articulate inferolaterally with the C1 superior facets, which face superomedially. The hypoglossal canal is located directly above the middle of the occipital condyle, facing anterolaterally at a 45-degree angle from the midsagittal plane. The intracranial opening of the hypoglossal canal is approximately 5 mm above the junction of the posterior and middle third of the occipital condyle and 5 mm below the jugular tubercle. The extracranial opening of the hypoglossal canal is approximately 5 mm above the junction of the anterior and middle third of the condyle and medial to the jugular foramen.
The transverse process of C1 is an important landmark, because it projects farther laterally than other transverse processes and is the attachment point for several muscles that will be dissected in this exposure. The anterior portion attaches to the rectus capitis. The posterior portion of the superior surface attaches to the superior oblique muscle, and the inferior and lateral surfaces attach to the inferior oblique, levator scapulae, splenius cervicis, and scalenus medius muscles.
Vertebral Artery
The LTA provides excellent exposure to the vertebral artery as it courses from C2 superiorly to the foramen magnum. The vertebral artery ascends laterally between the transverse foramen of C2 to C1 (see Fig. 6-1, B and C ). The vertebral artery then makes a sharp medial turn as it advances along the upper surface of the posterior arch of the atlas, passing the C1 nerve root and surrounded by the vertebral venous plexus. The vertebral artery then bends anteromedially as it enters the dural layer just adjacent to the occipital condyle.
Several muscular arterial branches arise from the vertebral artery during its course from the C2 transverse foramen to the foramen magnum. The posterior meningeal artery branches from the posterior surface of the vertebral artery, typically before it penetrates the dura in the region of the foramen magnum, but it may also have an intradural origin.
The C1 transverse process is a significant landmark, because the internal jugular vein and the eleventh CN lie anterior to it, and the vertebral artery can be followed coursing through the transverse foramen when the transverse process is removed. The C2 nerve root is an important landmark, where it traverses over the vertebral artery. The ventral rami of the C1 and C2 nerve roots pass behind the vertebral artery.
Cranial Nerves
After entering the dura, the lower CNs can be seen coursing from the brainstem to their exiting foramina. The transcondylar exposure will allow the dura to be reflected further laterally, thus providing a larger viewing angle. The rootlets of CNs IX to XI arise just posterolateral to the olive, and they exit via the jugular foramen and descend behind the internal carotid artery. Of note, CN XI has two distinct components, with cranial rootlets arising from the medulla that join lower rootlets arising from the spine at the level of the foramen magnum. CN XI will be the first CN encountered through this approach. The rootlets of CN XII arise from the medulla and pass anterior to the vertebral artery and exit via the hypoglossal canal.
Indications
Intramedullary
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Hemangioblastomas
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Cavernous malformations
Extramedullary, Intradural
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Meningiomas
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Hemangiopericytomas
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Schwannomas
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Paragangliomas
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Dermoid/epidermoids
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Vertebrobasilar aneurysms
Extradural
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Chordomas
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Metastases
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Epidural abscesses
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Rheumatoid pannus
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Bony compression
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Thoracic Microdiskectomy: Lateral and Posterolateral Approaches
Lumbar Facet Screw Fixation Techniques
Surgical Management of Scheuermann Kyphosis
Primary Malignant and Benign Tumors of the Spine
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