Cervical angiogram in the lateral projection. The internal carotid artery is divided into cervical and intra-cranial portions. The cervical portion of the internal carotid artery enters the carotid foramen of the skull and becomes the intra-cranial portion of the internal carotid artery. The intra-cranial portion is divided into 1) petrous, 2) cavernous, and 3)supra-clinoid portions.
The carotid canal is in the petrous portion of the temporal bone. There is a short (approx 1 cm) vertical portion and a longer horizontal portion. The artery exits the carotid canal, turns vertical once again and enters the cavervous sinus. Upon exiting the cavernous sinus it becomes the supra-clinoid portion.
 
Image on the left is a cervico-cerebral injection of the common carotid in an oblique projection. Image on the right is an injection into the internal carotid artery in the oblique projection centered on the bifurcation of the internal carotid artery. The supra-clinoid portion bifurcates into the anterior and middle cerebral arteries. From the bifurcation of the ICA to the anterior communicating artery is termed the A1 segment of the anterior communicating artery. From the bifurcation of the ICA to the first branching of the the middle cerebral artery is termed the M1 segment.
 
Both images from an injection into the internal carotid artery in the trans-orbital projection centered on the bifurcation of the internal carotid artery. Branches of the right middle and anterior cerebral arteries fill across a patent anterior communicating artery (ACOM). Branches of the anterior cerebral artery distal to the ACOM are A2 branches. Branches of the MCA from the first bifurcation are M2 segmental branches (supplying the insular cortex). The M3 segment are branches beyond the Sylvian fissure.
 
Both images from an injection into the internal carotid artery in the lateral projection. The first branch of the supra-clinoid portion of the ICA is the ophthalmic artery. The anterior cerebral artery is clearly seen above it in the lateral projection. The ACA divides into pericallosal and callosomarginal branches.
Normal Cerebral Arterial Anatomy |
