Anatomical landmark of sixth cranial nerve (abducens nerve)

1. ABDUCENS NERVE
IZMAL UROOJ
M.PHIL (OPTOMETRY) 1ST Semester

2. CRANIAL NERVES

3. INTRODUCTION
6TH CRANIAL NERVE
ABDUCENS = TO MOVE
AWAY
General SOMATIC
EFFERENT fibers
SUPPLIES LATERAL
RECTUS MUSCLE
abducens
NERVE

4. CRANIAL NERVE VI OR ABDUCENS
NERVE.
• abducens nucleus → only a somatic motor (general somatic
efferent) component
• Motor neurones supplying the ipsilateral lateral rectus, and
interneurones that pass through the medial longitudinal
fasciculus to the contralateral medial rectus.
• The abducens nucleus is located in the between the pons
and medulla oblongata.
• The sixth cranial nerve has a long subarachnoid course
• Innervates only one extra ocular muscle → Lateral rectus
muscle.

6. Embryology:
• The human abducens nerve is derived
from the basal plate of
the embryonic pons.

7. COURSE
• Passes upwards & anterolaterally in
subarachnoid space of posterior cranial
fossa
• Pierces the arachnoid & dura lateral to
the dorsum sellae(part of the sphenoid
bone)

8. • Arises between the layers of dura on the
posterior surface of the petrous bone
near its apex.
• Turns anteriorly to traverse the cavernous
sinus

9. • Enters the orbit through the superior
orbital fissure within the annular tendon
to supply the lateral rectus muscle

12. NUCLEUS
• Situated near the
midline in the
tegmentum of the
pons ventral to the
colliculus facialis
• Colliculus facialis is
an elevation in the
floor of the 4th
ventricle , produced
by the genu of facial
nerve.

15. INTERNUCLEAR NEURON
• About 40% of its neurons project into the
ipsilateral MLF only to cross over to the
contralateral side and ascend to innervate
that contralateral medial rectus
subnucleus to participate in contralateral
eye adduction.

16. ANATOMICAL LANDMARKS
SUPERFICIAL
EMERGENCE
POSTERIOR CRANIAL FOSSA
MIDDLE CRANIAL FOSSA
CAVERNOUS SINUS
SUPERIOR ORBITAL FISSURE
ORBIT

17. SUPERFICIAL EMERGENCE
• Emerges between
lower border of the
pons & lateral part of
the pyramid
• Emerge as seven or
eight rootlets

18. • abducens nerves are
about 1 cm apart
• Between them is the
Basilary Artery at its
formation from the two
vertebral Artery
• Lateral to each
abducens is the
emergence of the facial
Nerve at the lateral
side of the olive

19. 2.POSTERIOR CRANIAL FOSSA
Just after its emergence , the nerve is
crossed by the ANTERIOR INFERIOR
CEREBELLAR Artery
• Usually the artery is ventral , but it may
be dorsal or pass between the abducens
rootlets.

20. • Sleeved by the
piamater , it ascends
anterolaterally in the
cisterna pontis of the
subarachnoid space
between pons &
occipital bone

21. • At the upper border of the bone, it turns forward
at a right – angle under the Petro sphenoidal
ligament ( Gruber’s ligament )
• Thus passing through a canal called the Dorello’s
canal, to enter the cavernous sinus with the
inferior petrosal sinus
• Often the nerve pierces the inferior sinus,
entering the cavernous sinus within the inferior
petrosal sinus

24. 3.CAVERNOUS SINUS
• Here the nerve lies within the
cavernous sinus

26. Nerve is inferolateral to the horizontal
portion of the internal carotid artery with
its sympathetic plexus , which may
communicate with the nerve

27. • In the lateral wall of the
sinus , in descending
order are
• Oculomotor Nerve
• Trochlear Nerve
• Ophthalmic Nerve
• Maxillary Nerve
 abducens nerve is
usually in the sinus,
with a separate sheath

28. 4.SUPERIOR ORBITAL FISSURE
• Traverses the fissure
within the annulus of
Zinn
• At 1st below the
division of
oculomotor Nerve
• Then between them
& lateral to
nasociliary nerve

30. 5.IN THE ORBIT
• Nerve divides into 3
or 4 filaments which
enter the ocular
surface of lateral
rectus muscle behind
its midpoint

32. Coordination of Lateral Rectus and
Medial Rectus Muscles
• For eye movements in the horizontal plane, the lateral rectus muscle of
one eye and the medial rectus muscle of the other eye must work
precisely together.
• The actions of these muscles is coordinated by the lateral gaze center
located in the pontine reticular formation.
• Inputs from higher centers of the brain synapse in the lateral gaze center,
which then sends simultaneous signals to the ipsilateral abducens nucleus
and to the contralateral occulomotor nucleus via the medial longitudinal
fasciculus.
• The abducens nucleus sends signals via CN VI to the lateral rectus muscle
of the ipsilateral orbit to command that eye to be abducted.
• Simultaneously, the occulomotor nucleus generates a command via CN III
to contract the medial rectus muscle of the contralateral orbit resulting in
adduction of that eye.

33. BLOOD SUPPLY:
• Anterior inferior cerebellar artery, the
posterior inferior cerebellar artery, the
internal auditory artery, the anterolateral
artery, the pontomedullary artery, the
inferolateral pontine artery, the
anterolateral artery
• The majority of the of the abducens
nerves were supplied by the anterolateral
arteries, and only some of them by the
AICA, or the pontomedullary artery.

34. CLINICAL ASPECTS
LESIONSAT NUCLEUS
AT
FASCICULUS
PONTOMEDULL
ARY
JUNCTION
BASILAR
COURSE
IN
CAVERNOUS
SINUS

35. 1. At the level of nucleus
• Ipsilateral weakness of
abduction
• Failure of horizontal
gaze towards the side of
lesion.
• Ipsilateral facial nerve
palsy (lower motor
neurone)→involvement of
facial fasciculus.

36. AN ISOLATED 6TH NERVE PALSY IS
THEREFORE NEVER NUCLEAR IN ORIGIN.
In adults, the most likely etiology of
isolated sixth nerve palsy is ischemic
mononeuropathy that may be due to
diabetes mellitus, arteriosclerosis,
hypertension, temporal arteritis or
anemia

37. 2.PONTINE SYNDROMES – AT THE LEVEL OF FASCICULUS
• MILLARD GUBLER
SYNDROMEM
• RAYMOND CESTON
SYNDROMER
• FOVILLE SYNDROME
F

38. A. Foville syndrome
 Involves fasciculus as it
passes through PPRF
 5th nerve – facial
anaesthesia
 6th nerve + gaze palsy
 7th nerve – facial
weakness
 8th nerve – deafness
 Central horner
syndrome

41. B. Millard – Gubler syndrome
 Involves fasciculus as
it passes through the
pyramidal tract
 Ipsilateral 6th nerve
palsy
 Contralateral
hemiplegia (paralysis)

42. C. Raymond – Ceston syndrome
Due to tumor of cerebral peduncles
Red nucleus – speech & gait disorder
Paralysis of lateral conjugate gaze
Ipsilateral 6th Nerve palsy
5th nerve – facial anaesthesia
Contralateral hemiparesis

44. 3. At the pontomedullary junction:
ACOUSTIC NEUROMA:
• May damage the 6th
nerve → pontomedullary
junction.
• 1ST symptom –
hearing loss
• 1st sign - ↓ corneal
sensitivity

45. It is very important to test
hearing & corneal sensation in all
patients with 6th nerve palsy

46. 4. In the basilar course
A. Raised intracranial
tension:
• Downward displacement
of brainstem
• Stretching of 6th nerve
over petrous tip
• Bilateral 6th nerve palsy –
false localizing sign

47. B. Nasopharyngeal
tumors→ invade skull
and its foreman
C. Base of skull
fractures: → both
unilateral and bilateral
palsy

48. D. GRADENIGO’S SYNDROME:
• Mastoiditis/acute
Petrositis
• - damage to 6th nerve at
the petrous tip.
• Facial weakness
• Pain
• Hearing difficulties

49. 5. INTRACAVERNOUS PART
• Situated close to the
internal carotid Artery
• More likely to
damage than other
cranial nerves
 Intra cavernous 6th
nerve palsy is
accompanied by a
postganglionic
Horner’s syndrome

50. CLINICAL PRESENTATION
• HISTORY:
– Esotropia
– Head-turn
– Binocular diplopia (worse at distance)
– Vision loss
– Pain
– Hearing loss
– Symptoms of vasculitis, particularly giant cell
arteritis
– Trauma

51. abducens nerve palsy.

53. BCQ’S:
1. True statements of the abducens nerve
except:
a) Arises from the medulla
b) Passes under the petrosphenoidal ligament
c) May cross two venous sinuses in its course
d) Enters the orbit between the two divisions of III
e) May be damaged by raised intracranial pressure

54. • The abducens nerve nucleus:
a) Lies ventral to the genu of VII
b) Communicates indirectly with the nucleus of III
c) Sends fibres through Dorello's canal
d) Innervates lateral rectus on its extraconal surface

55. THANK
YOU