Microanatomical studies of the subtemporal anterior transpetrous keyhole approach

Objective To investigate the extent of the anterior petrous bone removal, the upper and middle clivus exposure, and operational techniques in the subtemporal keyhole approach, which can be regard as the base of this approach in clinical use. Methods The subtemporal keyhole approach was imitated in ten adult cadaveric heads fixed in 10% formalin and perfused intracranial vessels with colored silicone. Under operative microscope, the anatomic structures were observed and important structures were measured after the anterior petrous bone removal. Results The area of Kawase rhomboid construct and the rhomboid-shaped construct was 248.2±12.4 mm2 and 318.4±36.2 mm2 , respectively. They have significant variability. After opening the posterior fossa dura, the window offerred an access to the upper clivus, the middle basilar artery the midclivus inferior to the internal acoustic canal, the middle basilar artery, the inferior portion of pons, pontomedullary junction, the upper portion of medullary pyramid,the vertebrobasilar junction, the upper segment of vertebral artery, the anterior pontine and lateral pontine segment of the anterior inferior cerebellar artery. Abducens nerve, Dorello′canal, the origin of the anterior inferior cerebellar artery will be exposed after the removal of the petrous apex below the trigeminal impression. Conclusions It is feasible to maximally remove the anterior petrous bone and expose the upper and middle clivus through a craniecomy about 2 to 2.5 cm.