[Anatomic study on the design of far-lateral transcondylar transtubercular keyhole approach assisted by neuro-navigation].
OBJECTIVE
To design a new far-lateral transcondylar transtubercular keyhole approach assisted by neuro-navigation system according to the keyhole idea, and to explore the possibility of removing the occipital condyle and jugular tubercle precisely.


METHODS
Navigation data were established on 8 cadaveric heads fixed by formalin and with their intracranial vessels perfused with colored silicone. Before the operation, circumscriptions of the occipital condyle and jugular tubercle were outlined with different colors in the navigation system in order to aid drilling them in operation. A 7 cm longitudinal "S" shaped skin incision was performed with its superior border 2 cm behind the middle point of mastoid and inferior margin at the level of C(2). After inverting the suboccipital muscles and exposing the far lateral part of the occipital bone, occipital condyle, hemilamina of C(1), vertebral artery and posterolateral portion of foramen magnum, a retro-condylar bone flap 3 cm in diameter was cut. Assisted by neuro-navigation, not only were the maximal angle of visual field measured before and after the 1/3 and 1/2 posteromedial occipital condyle removal respectively, but also the anatomic structures were observed and measured.


RESULTS
The incision of the retro-condylar keyhole approach fully met the needs of the far-lateral transcondylar transtubercular keyhole approach; partial occipital condyle and jugular tubercle could be precisely drilled with the aid of neuro-navigation, thus avoiding the bewilder in drilling process; the maximal angles of visual field were 39.2 degrees +/- 3.29 degrees (before condyle drilled), 51.5 degrees +/- 2.45 degrees (1/3 condyle drilled) and 57.5 degrees +/- 2.66 degrees (1/2 condyle drilled) respectively, and there were significant difference among them (P < 0.01).


CONCLUSIONS
It is feasible to perform the far-lateral trascondylar transtubercular keyhole approach; the maximal angle of visual field is obviously increased by drilling partial occipital condyle, and the middle clivus can be increasingly exposed through removal of jugular tubercle.
Zhang
Heng-zhu
HZ
Department of Neurosurgery, Second Affiliated Hospital, Soochow University, Suzhou 215004, China.
Lan
Qing
Q