Carotid Arteries:  It is two large blood vessels that supply a majority of the brain with oxygenated blood from the heart. The carotid arteries course through the soft tissues of the neck and divide into the external and internal carotid arteries.  The 4 segments of the internal carotid artery (ICA) include the cervical (in the upper neck), petrous (in the skull base), cavernous (within the cavernous sinus alongside the pituitary gland) and supra-clinoid or cerebral segments.  The ICAs then bifurcate (divide) into the anterior and middle cerebral arteries and have connections through the Circle of Willis with the vertebro-basilar arterial complex (posterior circulation).  Being aware of the location of the cavernous carotid arteries is important during endonasal surgery given their close proximity to the pituitary gland.  Such localization is most easily done with the micro-doppler probe. Pituitary tumors and other skull base tumors such as meningiomas and chordomas can sometimes invade the cavernous sinus and surround the carotid arteries.