Circle of Willis and Vertebrobasilar

Question 1

Enumerate all the 10 components of the Circle of WIllis that create a nonagon.

Answer 1

Ten components
Internal carotid arteries (lCAs) (n = 2)
Posterior conununicating arteries (PCoAs) (n = 2)
Horizontal (AI) anterior conununicating artelies (ACoA) (n = 1)
Horizontal (AI) anterior cerebral arteries (ACAs) (n = 2)
Horizontal (Pt) posterior cerebral arteries (PCAs) (n = 2)
Basilar artery (BA) (n = I)

Question 2

What branches can be found in the circle of Willis?

Answer 2

Medial lenticulostriate arteries (from Al ACAs)
Recurrent artery of Heubner (usually from A2)
Thalamoperforating, thalamogeniculate arteries (from PCoAs, BA, PIs)

Question 3

What is the relationship of the PCoA to the optic tracts and oculomotor nerve?

Answer 3

It is below the tracts but above the oculomotor nerve

Question 4

How is the basilar bifurcation related to the brainastem structure?

Answer 4

The basilar bifurcation lies within the interpeduncular

fossa in front of the mid-brain.

Question 5

Remember the circle of willis is above the optic nerves and oculomotor nerve BUT bellow the _______. (part of a cranial nerve pathway)

Answer 5

Optic tracts

Question 6

What is the most common reason for failure of P1-PCA opacification with a vertebrobasilar injection?

Answer 6

Fetal PCA

Occurs in 20-30% of all injections

Question 7

How wide should an PCoA infundibulum be?

Answer 7

Less than 2mm, symmetric and wide at the BASE

Question 8

What is the most common circle of Willis variant?

Answer 8

Hypoplasia (right) or absence (left) of one or both posterior
communicating arteries (PCoAs) is the most common circle of Willis variant, seen in 25% to 33% of cases.

Question 9

By 5 weeks of development, what structures that will eventually become the vertebral arteries?

By the 4th week, what structures that will eventually become the basilar artery?

Answer 9

Cervical intersegmental arteries (C7 becomes the subclavian and from it arises the vertebral arteries0

Dorsal longitudinal arteries

Question 10

What are the four named segments of the vertebral artery?

Answer 10

l. The VI (extraosseous) segment
2. The V2 (foraminal) segment
3. The V3 (extraspinal) segment
4. The V 4 (inh’adural) segment

Question 11

Starting inferiorly what are the branches of the vertebral artery?

Answer 11

Cervical branches: spinal and muscular
Meningeal branches: Anterior and posterior meningeal
Intracranial: PICA and spinal arteries both anterior and posterior

Question 12

What transverse foramina . are traversed by the V2 segment?

Answer 12

C1-C6

Question 13

Where do the vertebral arteries unite to form the basilar artery?

Answer 13

At the pontomedullary junction

Question 14

What are the segments of the PICA?

How does it end?

Answer 14

Anterior medullary segment
Lateral medullary segment
Posterior medullary segment
Supratonsillar segment

The PICA then turns downward in the retrotonsillar fissure and terminates a short distance distal to the apex of the cranial loop by dividing into tonsillohemispheric (lateral) and vermian (medial) branches.

Question 15

What are the two meningeal branches of the extracranial vertebral artery?

Answer 15

Anterior and posterior meningeal arteries

Question 16

What is the usual dominant vertebral artery?

Answer 16

Left

The right is larger in only 25%

Question 17

How fenestration differ from duplication?

Answer 17

Fenestration (sometimes erroneously referred to as segmental duplication)
occurs when a vessel has a normal origin and position but has a double lumen for part of its course. Duplication implies that a
vessel has two origins that follow a more or less parallel course for a vmiable distance

Question 18

What is the most common anomaly of the vertebral artery?

Answer 18

Aortic origin of the VA.

Question 19

What are the embryonic precursors of the basilar artery?

Answer 19

Paired dorsal longitudinal arteries

Question 20

What are the normal measurements of the basilar artery?

Answer 20

3-4mm diameter by 32mm in length

Question 21

Where does the basilar artery bifurcate?

Answer 21

In 92% of cases, the terminal BA bifurcation is located in the interpeduncular cistern adjacent to the dorsum sellae

Question 22

How is the basilar artery related to the clivus?

Answer 22

It lies posterior to the clivus but anterior to the brainstem

Question 23

Where is the most common origin of the labyrinthine artery?

Answer 23

The anterior inferior cerebellar artery 45%

Question 24

Where does the labyrinthine artery go?

Answer 24

The artery goes to into the internal acoustic meati with CN8 and are distributed into the inner ears

Question 25

The superior cerebellar arteries contact what cranial nerve in half the anatomic dissections?

Answer 25

CN 5

Question 26

What part of the medulla can be supplied by the basilar artery?

Answer 26

Central

Peripheral usually by the PICA from the VA

Question 27

What supplies the ff cerebellar parts?

1. Superior cerebellum and upper vermis
2. Inferior and posterior cerebellum and inferior vermis
3. Petrosal surface

Answer 27

1. Superior cerebellum and upper vermis: SCA
2. Inferior and posterior cerebellum and inferior vermis: PICA
3. Petrosal surface: AICA

Question 28

What does the AICA look like on lateral view?

Answer 28

It has a double curve resembling an N or m on this view as the artery loops into the porus acusticus.

Question 29

When does the basilar artery appear to terminate by bifurcating into two SCAs?

Answer 29

When a fetal-type PCA is present in both sides and a vertebral artery injection is done.

Question 30

What is the incidence of a fenestrated basilar artery/

Answer 30

1.33% in anatomic dissections but is identified in only 0.12% of angiograms