Transcondylar Approach to the Craniocervical Junction

The far lateral approach and its variants consist of an inferior lateral suboccipital craniotomy, partial condyle resection, and C1 hemilaminectomy ( ▶ Fig. 3.1). The exposure provides an oblique and inferior trajectory that facilitates a lateral exposure of the lower clivus, anterior rim of the foramen magnum, odontoid process, anterolateral aspect of the medulla, and lower vertebral–basilar system without requiring retraction of the cerebellum, brainstem, or spinal cord.

Fig. 3.1 The far lateral approach consists of an inferior lateral suboccipital craniotomy, various degrees of condyle removal, and a C1 hemilaminectomy. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.)

3.2 Patient Selection

The appoach is applicable to a variety of conditions of the skull base, including both intradural and extradural neoplastic lesions, such as foramen magnum meningiomas, hypoglossal schwannomas, chordomas, and chondrosarcomas. The approach provides early proximal control of the vertebral artery and is optimal for aneurysms of the vertebral artery, posterior inferior cerebellar artery, and proximal vertebral–basilar system. Other vascular lesions, such as cavernous malformations of the medulla, are well suited for the approach. The far lateral approach is also useful for non-neoplastic inflammatory lesions of the odontoid, such as those found with rheumatoid arthritis, because it avoids the potential morbidity of the transoral approach.

The side of approach is typically dictated by the laterality of the lesion. For purely midline lesions, the local anatomy of the vertebral artery, venous sinuses, and jugular bulb aid in selecting the side of approach. The size and location of the pathology determine the necessary extent of bony removal. More extensive condylar resection increases the lateral exposure and provides access to more anteriorly located lesions.

Bone removal is catered to the lesion of interest, and thus multiple variations of the approach have been described. ¹^, ²^, ³^, ⁴^, ⁵^, ⁶^, ⁷^, ⁸^, ⁹ All versions of the approach include removal of the lateral aspect of the foramen magnum; however, the amount of removal of the occipital condyle needed varies from no resection as in the retrocondylar (without drilling the occipital condyle) variation of this approach to progressive removal of the condyle (transcondylar approach). In the extreme lateral infrajugular transcondylar approach, the exposure includes extradural resection of the jugular tubercle above the occipital condyle (supracondylar approach).

If a more superior target (vertebrobasilar junction) is to be approached, the jugular tubercle must be exposed, usually in an extradural fashion. Removal of this bony prominence improves lateral and superior visualization and allows access to the midclival region. Rarely, this exposure is required to access the vertebrobasilar artery or lower region of the basilar artery.

The hypoglossal canal runs obliquely along the superior aspect of the occipital condyle at a slightly upward trajectory (~ 45 degrees) with respect to the horizontal plane. The hypoglossal nerve, usually composed of multiple fascicles, is located within an osseous canal. As the drilling progresses during the transcondylar approach, the cortical bone, followed by cancellous bone, is thinned. As the nerve is approached, new cortical bone is reached. This osseous transition is important to preservation of the nerve. The hypoglossal nerve can be monitored electromyographically with electrodes placed on the tongue. Progressive drilling above the nerve proceeds to the jugular tubercle.

The vertebral artery is surrounded by a periosteal sheath. A venous plexus is adjacent to its second and third segment. Finally, the artery is encased in bone at the transverse foramen at C1. Appropriate venous coagulation and drilling of the transverse foramen at C1, and eventually at C2, permit medial mobilization of the vertebral artery to obtain the exposure needed to access the odontoid process from a posterior angle.

Progressive drilling of the occipital condyle widens the surgical exposure. Compared with a retrocondylar exposure, the angle of exposure increases by 30 and 40% if 25 or 50% of the occipital condyle is resected, respectively. ¹⁰ This maneuver minimizes retraction on the cerebellum and facilitates manipulation of surgical instruments.

The stability of the craniovertebral junction is based on the integrity of articular capsules (C1 facets and occipital condyle) and ligaments. The ligaments insert at the odontoid process and occipital condyle, especially the transverse and alar ligaments, respectively. Progressive removal of the condyle (> 50%) compromises the alar ligament, which causes instability and creates the need for occipitocervical fusion. Typically, we perform a fusion in patients when either surgical resection or the primary pathology compromises > 50% of the occipital condyle. ¹¹ Multiple techniques are available for that purpose.

3.3 Preoperative Preparation

Stereotactic image guidance is useful for surgery involving this region. Both magnetic resonance imaging and computed tomography are instructive for evaluation of soft tissue and bone. Evaluation of the venous drainage is necessary because neoplastic lesions in the region occasionally occlude the jugular bulb with collateral drainage through the condylar vein. Intraoperative electrophysiological monitoring is important. Somatosensory evoked potentials, brainstem auditory evoked responses, and specific cranial nerves (VII, XI, and XII) may be monitored, depending on the location of the lesion.

3.4 Operative Procedure

The patient is positioned laterally in a modified park-bench position with the head in rigid fixation ( ▶ Fig. 3.2). The head is flexed slightly and secured, rotated, and tilted. The dependent arm is supported under the Mayfield head-holder on a swing secured to the surgical table. The lower axilla is protected with a foam roll to prevent a brachial plexus injury.

Fig. 3.2 Head positioning is determined by the pathology that is being treated. The head is flexed and rotated or placed in a neutral position. In the modified park-bench position, the ipsilateral shoulder is pulled inferiorly to obtain an unobstructed field of view. (Reproduced with permission from Baldwin HZ, Miller CG, van Loveren HR, Keller JT, Daspit CP, Spetzler RF. The far lateral/combined supra- and infratentorial approach: a human cadaveric prosection model for routes of access to the petroclival region and ventral brain stem. J Neurosurg 1994;81:60–68.)

Multiple incisions have been proposed ( ▶ Fig. 3.3): a linear paramedian incision is useful for smaller lesions and likely diminshes the rate and size of pseudo-meningoceales, a C-shaped incision, and the inverted hockey stick and the large inverted U-shaped incision provide a wide exposure and are useful when bilateral occipital-cervical fusion is anticipated. The incision is catered to the condition being treated.

Fig. 3.3 Two different types of skin incisions. A straight-line incision (a) minimizes operative time but makes it harder to orient during the procedure. The horizontal portion of the vertebral artery is accessed quickly but is also threatened during dissection. Typically, a hockey-stick incision (b) is used. The short limb of the incision begins at the mastoid process and curves toward the superior nuchal line and the longer limb continues down to the level of the spinous process of C3 or C4. (Modified with permission from Baldwin HZ, Miller CG, van Loveren HR, Keller JT, Daspit CP, Spetzler RF. The far lateral/combined supra- and infratentorial approach: a human cadaveric prosection model for routes of access to the petroclival region and ventral brain stem. J Neurosurg 1994;81:60–68.)

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