Quantitative verification of the keyhole concept: A comparison of area of exposure in the parasellar region via supraorbital keyhole, frontotemporal pterional, and supraorbital approaches ; Laboratory investigation

Object. This study was designed to determine if the "keyhole concept," proposed by Perneczky's group, can be verified quantitatively. Methods. Fourteen (3 bilateral and 8 unilateral) sides of embalmed latex-injected cadaveric heads were dissected via 3 sequential craniotomy approaches: supraorbital keyhole, frontotemporal pterional, and supraorbital. Threedimensional cartesian coordinates were recorded using a stereotactic localizer. The orthocenter of the ipsilateral anterior clinoid process, the posterior clinoid process, and the contralateral anterior clinoid process are expressed as a center point (the apex). Seven vectors project from the apex to their corresponding target points in a radiating manner on the parasellar skull base. Each 2 neighboring vectors border what could be considered a triangle, and the total area of the 7 triangles sharing the same apex was geometrically expressed as the area of exposure in the parasellar region. Results. Values are expressed as the mean SD (mm2). The total area of exposure was as follows: supraorbital keyhole 1733.1 336.0, pterional 1699.3 361.9, and supraorbital 1691.4 342.4. The area of exposure on the contralateral side was as follows: supraorbital keyhole 602.2 194.7, pterional 595.2 228.0, and supraorbital 553.3 227.2. The supraorbital keyhole skull flap was 2.0 cm2, and the skull flap size ratio was 1:5:6.5 (supraorbital keyhole/ pterional/supraorbital). Conclusions. The area of exposure of the parasellar region through the smaller supraorbital keyhole approach is as adequate as the larger pterional and supraorbital approaches. The keyhole concept can be verified quantitatively as follows: 1) a wide area of exposure on the skull base can be obtained through a small keyhole skull opening, and 2) the side opposite the opening can also be visualized.