Illumination of mastoid air cell for suboccipital craniotomy: technical note.

The mastoid air cell was illuminated to estimate the location of the sigmoid sinus in 12 cases of a retrosigmoid suboccipital craniotomy for cerebellopontine angle tumors. A special illuminator system was designed, and the tip of the illuminator was placed inside the external auditory canal. The posterior margin of the illuminated air cell was delineated on the outer surface of the skull after the skin flap was turned and the position of the sigmoid sinus was estimated with reference to the preoperative computed tomographic scan. The posterior margin of the mastoid air cell in an axial slice, including the internal auditory canal, usually exists within the breadth of the sigmoid sinus. A gap between the posterior margin of the mastoid air cell and the position of the sigmoid sinus was easily corrected by the computed tomographic finding. This method was found to be simple and reliable in performing the suboccipital craniotomy with safety and exactness.