teaching MBBS students

1. ABDUCENT NERVE
DNM

2. INTRODUCTION

4. NUCLEUS ORIGIN
• Abducens nucleus originates
from the tegmenum pontis at
the level of facial colliculus.
• The nucleus is located;
1. anterior to the 4th ventricle,
2. posterior to the medial
Leminiscus,
3. Lateral to the medial
longitudinal fasciculus,
4. Medial to facial nerve &
trigeminal spinal nucleus.
The facial colliculus is a focal bulge in the floor of the
fourth ventricle formed by looping fibers of the
facial nerve around the abducens nucleus.

6. CONNECTIONS
ABDUCENT
NERVE NUCLEUS
MEDIAL
LONGITUDINAL
BUNDLE
OCULOMOTOR
NUCLEUS
TROCHLEAR
NUCLEUS
VESTIBULAR
NUCLEUS

9. The abducens nucleus contains 3 types
of neurons:
1.Abducens motor neurons which innervate the
ipsilateral lateral rectus muscle.
2.Abducens internuclear neurons, which project
to the contralateral medial rectus subnucleus
of the oculomotor nucleus via the medial
longitudinal fasciculus.(MLF)
3.Neurons that project to the cerebellar
flocculus

10. PARA PONTINE RETICULAR
FORMATION (PPRF)
• The gaze motor command involves specialized
areas of the reticular formation of the brain
stem which receive a variety of supra nuclear
inputs.
The main region for horizontal gaze is the
paramedian pontine reticular formation
(PPRF)

12. PPRF
IPSILATERAL
ABDUCENT
NUCLEUS
MLF
CONTRALATERAL
OCULOMOTOR
NERVE

13. ANATOMICAL LANDMARKS

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

15. COURSE
• Passes upwards & anterolaterally in
subarachnoid space of posterior cranial fossa
• Pierces the arachnoid & dura lateral to the
dorsum sellae

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

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

18. COURSE
• The abducens nerve
fascicle course antero-
inferiorly through the
pontine tegmentum
adjacent to the facial
nerve and exit from the
brain stem at the
ponto-medullary
sulcus.

19. • Cisternal segment
• Petro-clival segment
• Cavernous segment
• Orbital segment
• Dorello's canal is an osteofibrous conduit
located at the level of the petrous apex
through which the abducens nerve courses to
reach the cavity of the cavernous sinus

20. Cisternal segement
• courses superiorly
through the prepontine
cistern, to pierce the
dura over medial most
aspect of the petrous
ridge.

21. Petro-clival segment
• Dorello's canal is an
osteofibrous conduit
located at the level of
the petrous apex
through which the
abducens nerve courses
to reach the cavity of
the cavernous sinus

22. Cavernous segment
• The cavernous segment
of the abducens nerve
lie within the body of
the sinus unlike the
oculomotor , trochlear
& V1 & V2 divisions of
the trigeminal nerve
which lie within the
lateral wall of the sinus.

23. Orbital segment
• The abducens
nerve enters
the orbit
through the
superior
orbital fissure
and passes
through the
annular ring
of Zinn.

28. • 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

30. • In the lateral wall of the
sinus , in descending
order are
• Oculomotor .N
• Trochlear . N
• Ophthalmic. N
• Maxillary. N
 Abducent .N is usually in
the sinus, with a separate
sheath

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

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

33. CLINICAL ASPECTS
LESIONSAT NUCLEUS
AT FASCICULUS
PONTOMEDULLARY
JUNCTION
BASILAR
COURSE
IN
CAVERNOUS
SINUS

34. 1. At the level of nucleus
• ipsilateral weakness of
abduction
• failure of horizontal
gaze towards the side of
lesion
• ipsilateral LMN palsy of
facial nerve

35. AN ISOLATED 6TH NERVE PALSY IS THEREFORE
NEVER NUCLEAR IN ORIGIN

36. 2.PONTINE SYNDROMES – AT THE
LEVEL OF FASCICULUS
M
•MILLARD GUBLER SYNDROME
R
•RAYMOND CESTON SYNDROME
F
•FOVILLE SYNDROME

37. 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

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

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

40. At the pontomedullary junction:
 ACOUSTIC NEUROMA:
• 1ST symptom – hearing
loss
• 1st sign - ↓ corneal
sensitivity
• It is very important to
test hearing & corneal
sensation in all patients
with 6th nerve palsy

41. In the basilar course
 A. ↑ intracranial
tension:
• - downward
displacement of
brainstem
• - stretching of 6th nerve
over petrous tip
• b/l 6th nerve palsy –
false localizing sign

42.  B. nasopharyngeal
tumors
 C. base of skull fractures

43. D. Gradenigo’s syndrome:
 D. Gradenigo’s
syndrome:
• Mastoiditis/Petrositis
• - damage to 6th nerve at
the Dorello’s canal
• Facial weakness
• Pain
• Hearing difficulties

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

45. PHYSICAL FINDINGS
• An eso deviation that ↑
on ipsilateral gaze
• An isolated abduction
deficit
• Slowed ipsilateral
saccades
• Papilloedema
• Nystagmus
• Otitis media
• Orbital wall fracture
• Tender , non pulsatile
temporal arteries

46. CAUSES OF 6TH NERVE PALSY
ELEVATED INTRACRANIAL
TENSION
NEOPLASM
SUBARACHNOID SPACE
LESIONS
CONGENITAL ABSENCE
VASCULAR TRAUMATIC
METABOLIC POST LUMBAR TAP
DEMYELINATING DISEASE INFECTIONS

47. DIFFERENTIAL DIAGNOSIS
1. myasthenia gravis
2. restrictive thyroid myopathy
3. medial orbital wall blow out fracture
4. orbital myositis
5. duane syndrome
6. convergence spasm
7. divergence paralysis
8. early onset esotropia

48. WORK UP
• LAB TESTS:
• CBC
• Glucose levels
• HbA1C
• ESR/C – reactive protein
• Rapid plasma reagin tests
• Fluorescent treponemal antibody – absorption test
• Lyme titre
• Anti nuclear antibody test
• IMAGING STUDIES

49. IMAGING STUDIES
• CT
• MRI
• CEREBRAL ANGIOGRAPHY

50. MANAGEMENT
• Medical Care
• Truly isolated cases often are benign.
• They can be followed with a serial
examination, at least every 6 weeks, over a 6-
month period to note decreasing symptoms
(diplopia) and resolution of the paretic lateral
rectus (increasing motility)

51. • Children : Amblyopia treatment
• Older patients in whom giant cell arteritis is a
consideration should start the standard
treatment with prednisone or intravenous
methylprednisolone as soon as possible.

52. SURGICAL CARE
• INDICATION:
• If after 6 months of follow up care the
remaining deviation is still unacceptable & is
too large to be corrected with prisms

53. residual function exists
graded recession/resection

54. little or no residual function
transposition procedure
( weakening of antagonist
ipsilateral medial rectus
in appropiate patients )