A novel technique to avoid cerebrospinal fluid leaks following middle fossa approaches: Identifying a new triangle in the middle fossa.

Background: Skull-based approaches involving the middle fossa (MF) can be complicated by postoperative cerebrospinal fluid (CSF) leaks. Most of these CSF leaks are due to inadvertent entry into the eustachian tube (ET) or incomplete packing of surrounding air cells. Air cells are routinely plugged with bone wax during surgery; however, CSF leaks due to entry into the ET are often not recognized. Our objective was to define a safe zone for drilling that would avoid entry into the ET during MF approaches. Methods: Ten cadaveric specimens were fixed in formalin and injected with latex. Twenty sides were dissected and examined under a microscope. We exposed and identified the petrous internal carotid artery (ICA), ET, and all surrounding anatomical landmarks. Results: We identified a triangle bordered by the lateral aspect of the third division of the trigeminal nerve (V3), the lateral aspect of the petrous ICA, and an imaginary line through the middle meningeal artery connecting V3 to the petrous ICA. This triangle was then bisected at the base, creating a medial and lateral sub-triangle. In all 20 cadaveric exposures, the ET was in the lateral sub-triangle and did not extend into the medial sub-triangle. Conclusion: Our findings demonstrate that entry into the ET while exposing the petrous ICA during MF approaches can be safely avoided by drilling in the medial sub-triangle. Drilling in the lateral sub-triangle will lead to entry into the ET, increasing the risk of a postoperative CSF leak.