Microsurgical anatomy for lateral approaches to the foramen magnum with special reference to transcondylar fossa (supracondylar transjugular tubercle) approach

Microsurgical anatomy for lateral approaches to the foramen magnum, especia lly for transcondylar fossa (supracondylar transjugular tubercle) approach, was studied using cadavers. The transcondylar fossa approach is an approac h in which extradural removal of the posterior position of the jugular tube rcle through the condylar fossa is added to the far lateral approach. Some differences between this approach and the transcondylar approach are demons trated. The atlanto-occipital joint and the jugular tubercle are obstacles for the lateral approaches. The condylar fossa forming the external occipit al surface of the jugular tubercle is located supero-posterior to the occip ital condyle. The fossa is limited laterally by the sigmoid sulcus and the jugular foramen, or the hypoglossal canal opens at the bottom of the fossa. The condyle is situated inferior to the posterior condylar and the hypoglo ssal canals, and the jugular tubercle id located superior to them. In the t ranscondylar fossa approach the posterior part of the jugular tubercle is e xtradurally removed, but the condyle and the atlanto-occipital joint are un touched. On the other hand, in the trans condylar approach the medial parts of the condyle and the lateral mass of Cl are removed. The latter approach offer a better visualization of the inferior part of the foramen magnum. T he essential of the two approaches is in the direction of looking and the e xtent of resection of the atlanto-occipital joint. Both approaches offer ex cellent view of the ventral dural space in the lower clivus and the foramen magnum, but the level of exposure differs somewhat between them. In the la teral approaches to the foramen magnum, the condylar fossa, the posterior c ondylar canal, and the posterior condylar emisary vein all play an importan t role as intraoperative anatomical landmarks.