1. Anterior choroidal artery {source: neuroangio.org}

2. Embryologically, the anterior choroidal artery is very prominent during "choroidal" phase of embryogenesis (week 5 or so). Early on, the vertebrobasillar artery system is underdeveloped and the ICA supplies the entire brain-- the AChA supplies the PCA distribution. As the vertebrobasilar artery system develops more, the PCA takes over. In some people, this transition is incomplete and the AChA will continue to supply the cortical PCA territory particularly temporal lobes-- you may see 2 large vessels coming off terminal ICA. This is not a "duplicated PCA"
3. Choroidal arteries: 

4. Anterior choroidal on angiogram: {source: neuroangio.org}

Red: anterior choroidal
Cyan: plexal point (where artery enters choroidal fissure)
Pink + purple: perforators off AChA (ascend through perforator substance and supply optic tract and hypothalamus... these vessels are compromised in moya moya)
Orange: PComm
Dark Blue: meningiohypophyseal trunk
Lime green: Inferolateral trunk
5. Anterior view of anterior choroidal on angiogram: {source: neuroangio.org}

6. The PComm almost always arises proximal to the AChA, with very rare exceptions. Do not confuse the two! If you have a Pcomm aneurysm you can sacrifice the Pcomm, but you cannot sacrifice the AChA!!!! See angiogram here {source: neuroangio.org}

Red: AChA, hemispheric branch of AChA
Purple: choroidal part of AChA
Orange: PComm
7. Anterior Choroidal Artery territory infarct: {Source: Derflinger et al, Int J Stroke}

8. Diagram of anterior choroidal distribution: {source}

9. Anterior Choroidal artery supplies:
Cisternal segment:
- Optic tract
- Lateral geniculate nucleus
- Posterior limb of internal capsule (some redundant supply from lenticulostriate arteries)
- Midbrain
Ventricular segment:
- Choroid plexus of lateral and third ventricles.
10. Infarcts in AChA can cause
- Contralateral hemiplegia
- Hemianesthesia
- Contralateral homonymous hemianopsia.