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Anatomy of the Nervous System

Vertebral Artery!!navigator!!

originates from subclavian a. proximal to thyrocervical trunk; left vertebral a. usually greater than right cerebral a.; left vertebral a. may originate directly from aorta (5%)

  1. PREVERTEBRAL SEGMENT (V1)
    ascends posterosuperiorly between longus colli + anterior scalene muscle; enters transverse foramen at C6
    Branches: muscular branches
  2. MIDCERVICAL SEGMENT (V2)
    ascends through transverse foramina of C6 to C2 in close proximity to uncinate processes
    Branches:
    1. Anterior meningeal a.
  3. ATLANTIC SEGMENT = Atlas loop (V3)
    exits transverse foramen of atlas; passes posteriorly in a groove on superior surface of posterior arch of atlas; pierces atlanto-occipital membrane + dura mater to enter cranial cavity
    Branches:
    1. Posterior meningeal branch to posterior falx + tentorium
  4. INTRACRANIAL SEGMENT (V4)
    ascends anteriorly + laterally around medulla to reach midline at pontomedullary junction; anastomoses with contralateral side to form basilar artery at clivus
    Branches:
    1. Anterior + posterior spinal a.
    2. Posterior inferior cerebellar a. (PICA)
    3. Anterior inferior cerebellar a. (AICA)
    4. Internal auditory a.
    5. Superior cerebellar a.
    6. Posterior cerebral a. (PCA)
    7. Medullary + pontine perforating branches
    • May terminate in common AICA-PICA trunk

Anterior Inferior Cerebellar Artery!!navigator!!

= AICA = first branch of basilar artery

Supply: lateroinferior part of pons, middle cerebellar peduncle, floccular region, anterior petrosal surface of cerebellar hemisphere

  • Quite variable course + vascular supply with reciprocal relation between vascular territories of AICA + PICA!

Posterior Inferior Cerebellar Artery!!navigator!!

= PICA = last and largest branch of vertebral artery

Supply: inferoposterior surface of cerebellar hemisphere adjacent to occipital bone, ipsilateral part of inferior vermis, inferior portion of deep white matter only

Parts:

  1. Premedullar segment = caudal loop around medulla, may descend below level of foramen magnum
  2. Retromedullar segment = ascending portion up to the level of 4th ventricle and tonsils
  3. Supratonsillar segment = the most cranial point is the choroidal point

P1 segment = horizontal segment between origin of PICA + pCom

P2 segment = segment downstream from pCom take-off

Variations: commonly asymmetric; hypoplastic / absent in 20% [vascular supply then provided by anterior inferior cerebellar artery (AICA)]

Orthotopicchoroid pointestablished by:

  1. perpendicular line from choroid point onto Twining's line = TTT-line (Twining's Tuberculum-Torcular line) bisects TTT-line (length of anterior portion 52–60%)
  2. perpendicular line from choroid point cuts CT-line (Clivus-Torcular line) <1 mm anterior / <3 mm posterior to junction of anterior and middle thirds of CT-line

Superior Cerebellar Artery!!navigator!!

= SCA = last but one branch of basilar artery

Supply: superior aspect of cerebellar hemisphere (tentorial surface), ipsilateral superior vermis, largest part of deep white matter including dentate nucleus, pons

Outline