Intracranial Anatomy

Question 1

ICA segments

Answer 1

1. Cervical ICA. From carotid bifurcation to canal of petrous portion of temporal bone.
2. Petrous ICA. Through petrous portion. Cannot see with US.
3. Cavernous ICA aka Carotid Siphon. Consist of parasellar portion, genu portion (the bend), and supraclinoid portion.

Ophthalmic artery arises from cavernous portion of ICA.

ICA terminates into Middle cerebral artery and anterior cerebral artery.

Question 2

Middle cerebral artery

Answer 2

Courses laterally. Carries 75-80% of ICA flow. Larger than Anterior cerebral artery.

Question 3

Anterior cerebral artery

Answer 3

Courses medially. Gives rise to anterior communicating artery to connect RT and Lt anterior cerebral arteries.

Question 4

Vertebral - Basilar system

Answer 4

Vertebral arteries arise from subclavian. Course between transverse processes of spine. Enter skull at foramen magnum.

Basilar artery is form by confluence of 2 vertebral arteries. About 3 cm long. Basilar artery bifurcates into 2 posterior cerebral arteries.

Question 5

Posterior cerebral arteries

Answer 5

Perfuse posterior hemispheres

Give rise to posterior communicating arteries which connects anterior circulation.

Can arise from ICA in 20% of population.

Question 6

Circle of Willis

Answer 6

50% of population have intact circle of Willis

Only 25% have classic configuration.

Question 7

Transcranial Doppler access windows

Answer 7

1. Transorbital
2. Submandibular
3. Suboccipital / transforaminal
4. Transtemporal