To observe the range of exposure, indications and feasibility of retromastoid keyhole approach through drilled petrous ridge to the middle fossa.

The eight adult cadareric heads in this study were provided by the anatomy laboratory of the second affiliated hospital of Soochow Univer sity. Simulated surgeries via retromastoid keyhole approach with assistance of neuroendoscope were performed on 8 adult cadaveric heads (16 sides) fixed by formalin and the maximal ranges of exposure were observed. The neuroendoscope was used to observe anatomical structures in the middle fossa and identify the limits of the Parkinson's triangle. The distances from the posterior border of junction of lateral sinus and sigmoid sinus to middle fossa and the length of all sides of Parkinson's triangle were measured.

Identified under endoscope, the exposure range of this approach included cerebellopontine angel (CPA), ventrolateral brainstem, tentorial incisure, petroclival region and lateral wall of cavernous sinus. The exposed anatomical structures in the middle fossa included trigeminal ganglion, cavernous segment of trochlear and abducent nerve, petroclinoid segment of oculomotor nerve, posterior curve segment of internal carotid artery (ICA) in cavernous sinus, communicating segment of ICA and posterior communicating artery (PCoA). Measurement results suggested that the distances from the midpoint of posterior border of sigmoid sinus to suprameatal tubercle, trigeminal ganglion, posterior curve segment of ICA were 34.4±2.1 mm, 54.5±2.9 mm and 65.2±3.1 mm, respectively. The lengths of all sides of Parkinson’s triangle were 19.0±2.9 mm, 16.2±2.0 mm and 8.0±2.3 mm, respectively.

The retromastoid keyhole approach via drilled petrous ridge leads to feasible exposure of the middle fossa under neuroendoscope, which could be applied in operations of most lesions in the posterior fossa such as tumors and aneurysms as well as those mainly in the posterior fossa and minorly affecting the middle fossa.

Mastoid; Anatomy; Neurosurgical procedures