Far Lateral Suboccipital (Transcondylar) Approach
The far lateral suboccipital and its variants, including the supra-, para- and trans-condylar approaches, have been developed to expose pathologies at the ventral and ventrolateral craniovertebral junction. This region includes the space anterior to the brainstem and the spinal cord, extending from the jugular bulb to the upper cervical spine.
This ventral region is difficult to reach microsurgically, and modifications of the far lateral suboccipital pathway require varying degrees of bony resection so that the pathology can be reached without retraction on the medulla oblongata and upper spinal cord. Anterior routes, such as the transnasal endoscopic and transoral trajectories, are reserved primarily for extradural lesions; the lateral corridors are preferred for intradural pathologies.
The far-lateral transcondylar approach entails a suboccipital craniotomy posterior to the sigmoid sinus and C1 hemilaminectomy followed by partial or complete resection of the ipsilateral occipital condyle. I rarely extend the condylectomy only to the point of adequate exposure because excessive condylar resection (>30%) increases the risk of occipitocervical instability and a need for occipitocervical fusion. This arthrodesis greatly limits the patient’s neck mobility. The far lateral approach without violation of the condyle is all that is needed in almost all cases.
In addition to the far-lateral transcondylar approach, extreme-lateral transcondylar and transjugular procedures have been described for extensive extradural lesions in this area. These approaches involve a complete condylectomy and partial mastoidectomy, and they provide wide exposure of the anterior craniovertebral junction. Yet they are associated with a high risk of surgical morbidity, require occipitocervical fusion, and have few if any indications. Therefore, I describe only the far-lateral approach here.
Indications for Far Lateral Approach
The most common indications for far lateral approach are:
- Anterior craniocervical junction intradural tumors, such as meningiomas or lower cranial nerve schwannomas.
- Vascular lesions, such as ventral aneurysms of the distal vertebral arteries and anterior lower brainstem cavernous malformations.
- Extradural clival lesions, such as chordomas, chondrosarcomas, metastases, or glomus jugulare tumors (the former two tumors are best approached through the transnasal endoscopic corridor).
Magnetic resonance (MR) imaging demonstrates the rostral-caudal extent of the tumor and guides the size of the suboccipital craniotomy. In addition, the ventral-lateral location of the lesion dictates the necessary extent of condylectomy. Brainstem and spinal cord edema and tumor calcification indicate pial invasion and correlate with development of postoperative neurologic decline since some degree of pial manipulation is necessary to mobilize the tumor. In these cases, a subtotal resection, while leaving a thin sheet of the tumor on the pia and surrounding vessels to protect the perforators, is recommended. Encasement of vessels and infiltration of the tumor into the jugular foramen (encasement of cranial nerves) are other indications for subtotal resection.
Imaging studies should include computed tomography (CT) or catheter angiography to evaluate the relationship of the adjacent vasculature (vertebral artery, intradural versus extradural origin of the posterior inferior cerebellar artery) to the pathology and the laterality of vertebral artery’s dominance. This information affects the safety of sacrificing the ipsilateral vertebral artery proximal to the posterior inferior cerebellar artery. Highly calcified tumors can present daunting challenges in their resection and require decompressive surgery because they encase neurovascular structures.
The patient’s preoperative evaluation should include a thorough neurologic and otolaryngologic exam with particular attention to the lower cranial nerves. Detailed evaluations of the swallowing and vocal cord functions are necessary. If there is concern regarding preoperative lower cranial nerve palsy, the patient should be informed of the need for a tracheostomy and/or gastrostomy postoperatively. Malnourished patients affected by preoperative swallowing dysfunction should be treated first through nutritional consultation to minimize the risk of postoperative wound breakdown or overall recovery,
After these evaluations, the surgeon plans the expected extent of condylar resection based on a detailed study of the MR and CT images. As I mentioned above, the far lateral approach without violation of the condyle is all that is needed in almost all cases. In very rare cases, I believe the removal of less than 30% of the condyle may be needed to safely resect isolated ventral lesions. Almost always, the pathologic lesion itself has widened the required operative corridor toward the anterior brainstem and eliminates the need for more extensive condylar resection.
I do not advocate medial mobilization of the vertebral artery (extreme far lateral approach) to further the condylectomy. In fact, this maneuver is unnecessary and increases the risk of injury to the artery and hypoglossal nerve and portends biomechanical instability.
Intraoperative monitoring of brainstem auditory evoked responses (BAERs) and somatosensory evoked potentials (SSEPs) as well as electromyographic monitoring of cranial nerves VII, X, XI, and XII are recommended.
The following images from Dr. Albert Rhoton’s work further illustrate the relevant surgical anatomy described later in this chapter. A detailed understanding of the complex anatomy of the craniocervical junction is important for complication avoidance.
FAR LATERAL OSTEOTOMY
Patient positioning and the degree of head rotation can substantially affect the operative corridor during this approach.
I avoid significant neck rotation, but slightly turn the patient’s head toward the floor to maintain the relative normal anatomic course of the vertebral artery at the craniocervical junction for surgical orientation.
A number of different incisions, including the “lazy S” and “reserve U” incisions, have been described for transcondylar route. I use the traditional hockey-stick incision because it minimizes dissection through the neck muscles and mobilizes the myocutaneous flap laterally out of my working zone.
Once the myocutaneous flap is mobilized laterally, great care must be taken to identify the vertebral artery in its sulcus over the lateral arch of C1 and avoid its injury. Once subperiosteal dissection reaches the lateral half of the C1 lamina, electrocautery is abandoned in favor of meticulous sharp and blunt dissection to identify the artery and its encasing venous plexus.
The myocutaneous flap is then secured with fishhooks, and I use a fine curette to dissect the atlanto-occipital ligament away from the edge of the foramen magnum and the hemilamina of C1. The vertebral artery is then followed into the transverse foramen. The posterior arch of the atlas and its lateral mass are also exposed in a subperiosteal fashion. The ligaments around the artery are microsurgically dissected so that the artery can be mobilized laterally during reflection of the dura.
Venous bleeding from the periarterial plexus can be controlled using low-amplitude bipolar coagulation or thrombin-soaked Gelfoam packing and tamponade.
If a more extensive condylectomy is absolutely necessary, the surgeon must prevent injury to the hypoglossal nerve as it courses through the superior aspect of the anterior third of the condyle.
The superior articular process of the C1 lateral mass may also be partially removed. Resection of half or more of the occipital condyle results in biomechanical instability and necessitates occipitocervical arthrodesis.
The dural edges are tacked up using 4-0 sutures and kept moist throughout the operation to avoid their desiccation by the intense heat of the microscope, facilitating watertight closure. The tack-up stiches are placed along the bony edges (the most anterior aspect of the exposed dura) to maximize mobilization of the dural flaps away from the operative trajectory. This maneuver mobilizes the vertebral artery as it enters the dura, laterally and out of the working trajectory of the surgeon.
The cisterna magna may be opened to drain cerebrospinal fluid, relax the cerebellum, and improve exposure without the use of fixed retraction. At this point, the relevant pathology is addressed.
Once the pathology is surgically treated, absolute hemostasis is achieved in the operative site and the surgeon’s attention turns to closure. The subarachnoid space is copiously irrigated, and the dura is closed primarily, if possible, or via a dural graft. Every effort must be made to achieve a watertight closure. I do not routinely replace the bone flap or complete a cranioplasty because the bony defect is small. There is no concern regarding delayed instability in the craniospinal junction after the above approach. The soft tissues are then closed in the anatomic layers.
Pearls and Pitfalls
- Condylectomy rarely if ever is needed. A partial condylectomy (<30%) suffices to achieve adequate exposure of the anterior aspect of the brainstem in very rare cases.
- Preoperative studies should evaluate vertebral dominance and exclude the possibility of the ipsilateral vertebral artery ending only in the posterior inferior cerebellar artery. Any aberrant location of the dolichoectatic vertebral artery extending outside its sulcus arteriosus and hiding within the posterior muscle layers should be noted. In this variation, the artery is vulnerable to injury during dissection.
- Muscular branches of the vertebral artery tether the artery to the posterior soft tissues; these branches should be carefully coagulated and transected. Their avulsion injury may lead to parent vessel occlusion.
- To protect the vertebral artery, I avoid monopolar electrocautery on the lateral half of the C1 lamina as the posterior wall of the sulcus arteriosus may be incompetent. Aggressive coagulation of the vertebral venous plexus should be avoided to prevent arterial injury. Thrombin-soaked Gelfoam may be used to achieve hemostasis.
For additional illustrations of the far lateral approach to the foramen magnum, please refer to the Jackler Atlas by clicking on the image below:
For additional illustrations of infratemporal fossa approaches, please refer to the Jackler Atlas by clicking on the image below:
For additional illustrations of transjugular craniotomy, please refer to the Jackler Atlas by clicking on the image below:
Al-Mefty O. Operative Atlas of Meningiomas. Lippincott-Raven, Philadelphia, PA; 1998.
Cusimano M, Faress A, Chang Y, et al. Foramen magnum meningiomas. In DeMonte F, McDermott M, Al-Mefty O, eds, Al-Mefty’s Meningiomas, 2nd ed. Thieme Medical Publishers, New York, NY; 2011:297–306.
Sen C, Shrivastava R, Anwar S, et al. Lateral transcondylar approach for tumors at the anterior aspect of the craniovertebral junction. Neurosurgery 2010;66:A104–A112. doi.org/10.1227/01.NEU.0000365930.95389.60.
Sen C, Sekhar LN. Extreme lateral transcondylar and transjugular approaches. In Sekhar LN, Janecka IP, eds, Surgery of Cranial Base Tumors. Raven Press, New York, NY; 1993:389–411.
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