Anatomy and imaging of cranial nerves 3,4 and 6

1. CRANIAL NERVES III,IV AND VI
Dr Parvathy S Nair

2. CRANIAL NERVE III(OCCULOMOTOR)

3. • Occulomotor nucleus (in front of cerebral aqueduct at level
of superior colliculus of midbrain and exits ventrally in
interpeduncular fossa)
• Four lateral paired subnuclei that innervate the superior,
inferior, and medial rectus, as well as the inferior oblique
muscles.
– Axons from one superior rectus (SR) nucleus cross and pass
through the opposite SR subnucleus; thus, a lesion of one SR
subnucleus results in bilateral superior rectus palsy.
– LPS has also bilateral supply
– All other EOM gets ipsilateral supply
• Edinger-Westphal (parasympathetic)nucleus, which
contains preganglionic, parasympathetic neurons whose
axons project to the ciliary ganglion and postganglionic
paraympathetic fibres supply sphincter pupillae and ciliaris
muscle

7. Course
• The oculomotor nerve exits the ventral midbrain
in the interpeuncular fossa-> pierces the dura
mater-> between PCA above and SCA below
• Through the lateral wall of the cavernous sinus,
enters orbit through superior orbital fissure.
• Within the orbit it branches into a superior
ramus (to the superior rectus and levator
muscles) and an inferior ramus (to the medial
and inferior rectus, the inferior oblique, and the
ciliary ganglion).
• Postganglionic fibres from the ciliary ganglion
innervate the sphincter pupillae muscle of the iris
as well as the ciliary muscle.

11. Functions
• EOM- all movements except lateral and downand-out movements
• Levator palpabrae superioris-same branch as
that of SR- elevation of lid
• Parasymp. innervation- miosis,accomodation
and light reflex

13. CRANIAL NERVE IV(Trochlear)
• Long course
• Emerges from trochlear nu at the level of
inferior colliculus
• Connections-same as CN3
• COURSE-After winding around the
periaqueductal grey matter and comes out
posteriorly through the opposite side
• Crosses the tentorium->enters middle cranial
fossa->lat wall of cavernous sinus->enters
SOF->supplies Sup. Oblique muscle.

17. Functions
• Down and out movement of eyeball
• “Reading muscle”
• Intorsion – axis of vision is kept parallel

18. CRANIAL NERVE VI(ABDUCENS)
• The abducens nucleus is located in the pons, on
the floor of the fourth ventricle, at the level of
the facial colliculus.
• Connections-same as CN3
– PPRF connections-lateral conjugate gaze
• Course- exits from pontomedullary jn->runs
between AICA and labrynthine artery->At the tip
of the petrous temporal bone it makes a sharp
turn forward to enter the cavernous sinus.
• In the cavernous sinus it runs alongside the ICA.
It then enters the orbit through the SOF and
innervates the lateral rectus.

21. • Abducent palsy is seen in increased ICT- due
to compression against the petrous apex
causing “false localization sign”
• FUNCTION– Lateral movement of eye
– Lat conjugate gaze

22. Examination
• 3,4,6 can be examined together
– Ask patient to look up, down, obliquely up and
down
– Each eye separately
• Parasympathetic function-only for CN 3
– Pupillary light reflex
– Accomodation reflex

23. MR Imaging of normal CN3,4,6
• Difficult to evaluate the cisternal segments of
the cranial nerves, which are small in diameter
and are located in close proximity to many
other anatomic structures.
• Thin T2WI(1mm thickness)
• SSFP/PSIF sequences depict these nerve
segments in greater detail
• Type of coherent GRE sequence
• 0.8mm thick-ideal

27. LESIONS

28. CN III
• Diabetic occulopathy
– External ophthalmoplegia
– Pupils are spared
• Compressive lesions
– Aneurysms –PCA,Pcom,SCA
– Tumors
– Outer fibres-pupillary paralysis
• Inflammation-CST, Tolosa Hunt
• Demyelination
• Infections-TB

29. • External ophthalmoplegia
– All EOM except LR and SO are affected
– Eye turned down and out
– Diplopia becoming better on looking to paralysed
side
• Ptosis- LPS
• Lateral gaze palsy – Medial longitudinal
fasciculus
• Parasympathetic loss– Mydriasis
– Cycloplegia

33. CN IV
• Aneurysm of internal carotid
• Cavernous sinus thrombosis
• Diplopia-on looking down
• Medial deviation of affected eye
• Head tilted towards the normal side

35. CN VI
• Medial deviation of eye
• Diplopia –becoming worse on looking to the
paralysed side

38. THANKYOU