A, Inferior view of the occipital condyles and foramen magnum. The occipital condyles are ovoid structures located along the lateral margin of the anterior half of the foramen magnum. The hypoglossal canal, through which the probe has been passed, is located above the middle third of the occipital condyle and is directed from posterior to anterior and from medial to lateral. The intracranial end of the hypoglossal canal is located approximately 5 mm above the junction of the posterior and middle third of the occipital condyle, and approximately 8 mm from the posterior edge of the condyle. The extracranial end of the canal is located approximately 5 mm above the junction of the anterior and middle third of the condyle. The far lateral approach is directed through the area behind the condyle, and the transcondylar approach involves removal of some of the condyle. The large arrow shows the direction of the transcondylar approach and the hatched area shows the portion of the occipital condyle that can be removed without exposing the hypoglossal nerve in the hypoglossal canal. B, Right side. A suboccipital craniectomy has been completed and the right half of the posterior arch and the posterior root of the transverse foramen of the atlas have been removed. The vertebral artery passes medially behind the atlanto-occipital joint. A posterior condylar vein passes through the occipital condyle. C, The drilling in the supracondylar area exposes the hypoglossal nerve in the hypoglossal canal and can be extended extradurally to the level of the jugular tubercle to increase access to the front of the brainstem. The dura has been opened. The dural incision completely encircles the vertebral artery, leaving a narrow dural cuff on the artery so that the artery can be mobilized. D, Comparison of the exposure with the far lateral and transcondylar approaches. On the right side, the far lateral exposure has been extended to the posterior margins of the atlantal and occipital condyles and the atlanto-occipital joint. The prominence of the condyles limits the exposure along the anterolateral margin of the foramen magnum. On the left side, a transcondylar exposure has been completed by removing the posterior part of the condyles. The dura can be reflected further laterally with the transcondylar approach than with the far lateral approach. The condylar drilling provides an increased angle of view and room for exposure and dissection. The dentate ligament and accessory nerve ascend from the region of the foramen magnum. (Images courtesy of AL Rhoton, Jr.)