Localization of the Internal Maxillary Artery for Extracranial-to-Intracranial Bypass through the Middle Cranial Fossa: A Cadaveric Study.

The internal maxillary artery (IMAX) is a promising arterial pedicle to function as a donor vessel for extracranial-to-intracranial (EC-IC) bypass procedures. The access to the IMAX through the anterior portion of the middle cranial fossa floor allows a much shorter interposition graft to be used to create a bypass to the ipsilateral middle cerebral artery and prevents a second incision in the neck. One of the challenges of this technique, however, is the difficulty to find the IMAX through an intracranial approach. The purpose of this cadaveric study is to establish a reliable method to localize the IMAX through a middle fossa floor approach based on skull base bone landmarks. In this study 5 latex-injected fixated cadaveric specimens were dissected bilaterally (providing a total of 10 IMAX dissections) to determine the precise location of the IMAX in the pterygopalatine fossa in relationship to bone landmarks of the middle fossa floor as seen through an intracranial approach. Drilling of the middle fossa floor was undertaken through both the originally described "anteromedial" approach, and a new "anterolateral" approach. Measurements were taken correlating the position of the IMAX to ipsilateral foramen rotundum, ipsilateral foramen ovale, posterior wall of the maxillary sinus, and distal V2 branches. Median and standard deviation were calculated for each dataset. The IMAX was found, within the pterygopalatine fossa, by drilling the greater wing of the sphenoid bone on average 10 mm anteriorly and 5 mm laterally to foramen rotundum, at an average depth of 8 mm. The IMAX was also found inferiorly to the maxillary nerve and laterally to the pterygoid head of the lateral pterygoid muscle. A more laterally oriented approach, consisting of drilling the greater wing of the sphenoid bone from a point perpendicular to foramen rotundum posteriorly to the sphenotemporal suture anteriorly, allowed for a longer segment of the IMAX to be easily identified and exposed facilitating its use as a donor vessel in bypass procedures. This cadaveric study provides a reliable and reproducible set of measurements to localize the IMAX within the pterygopalatine fossa through an intracranial middle fossa approach. The ability to find the IMAX consistently is an important step in exploring the possibility of using the IMAX as a routine donor vessel for EC-IC bypass procedures.