Internal carotid artery (ICA)

Petrous (C2) segent

Contained within carotid canal of temporal bone

• Surrounded by extensive sympathetic plexus

• Two C2 subsegments joined at genu

  • Short vertical segment - anterior to internal jugular vein (lJV)

  • "Genu" (where petrous ICA turns anteromedially in front of cochlea)

  • Longer horizontal segment

    • Exits carotid canal at petrous apex

    • Branches

      • Vidian artery (artery of pterygoid canal) anastomoses with external carotid artery (ECA)

      • Caroticotympanic artery (supplies middle ear)

Lacerum (C3) segment

• Small segment that extends from petrous apex above foramen lacerum, curving upwards toward cavernous sinus

• Covered by trigeminal ganglion

• No branches

Cavernous (C4) segment

• Three subsegments joined by two genus (knees) -

  • Posterior vertical (ascending) portion

  • Posterior (more medial) genu

    • Meningohypophyseal trunk (arises from posterior genu, supplies pituitary, tentorium and clival dura)

  • Horizontal segment

    • Inferolateral trunk arises from horizontal segment, supplies cavernous sinus (CS) dura / cranial nerves; anastomoses with ECA branches through foramens rotundum, spinosum, ovale

  • Anterior (more lateral) genu

  • Anterior vertical (subclinoid) segment

• Covered by trigeminal ganglion posteriorly

• Abducens nerve (CN6) is inferolateral

Clinoid (C5) segment

• Between proximal, distal dural rings of cavernous sinus

• Ends as ICA enters subarachnoid space near anterior clinoid process

• No important branches unless ophthalmic arteries arises within C5