4th cranial nerve

what is 4th nerve name?

trochlear nerve

supplies SO

incyclorotation, depression, abduction

inv

-          CT: HyperT – SO works at N

o    V pattern – bilat

o    Possible E in dev

-          OM: SO u/a

o    o/a of contralat IR and ipsilat I/O

o    Knapps classification

o    limited elevation/ depression in adduction

o    BHTT

-          AHP: chin depression

-          Conv – reduced – CI

-          Torsion: bilat – excyclo

-          Hess: field displaced upward to affected side

-          Vertical prism fusion range

-          Lateral gaze mx

-          Diplopia: vertical + uncrossed - subjective torsional

can be both, congenital longstanding decompensating 4th CNP common

-          Field of BSV

describe the course of the 4th nerve

nuclei in midbrain, nerves cross over as it leaves the brainstem, right 4th nuclei supplies left SO etc., wraps around back and side of brainstem and moves forward into subarachnoid space, enters cavernous sinus, supplies SO

where is the 4th nerve nuclei located?

in the dorsal midbrain, specifically at the level of the inferior colliculus

describe the location of the 4th in the cavernous sinus

located in the lateral wall, inferior to the 3rd nerve
superior to 5th nerve

list aetiologies of an acquired 4th NP in the subarachnoid space?

high ICP
ischaemia
intrinsic lesions e.g schwanomma
aneurysm
trauma
venous malformations
carotid-cavernous fistula
basal meningitis

list the aetiologies of an acquired 4th NP in the orbital

-          Ischemic – hypertension, diabetes

-          Compressive – tumour, aneurysm, stroke

-          Traumatic – head or orbit

-          Congenital

what would you observe in a pt with 4th CNP

facial asymmetry - cheekbones flatter on oneside in congential
headposture
FAT family album tomography scan - looking at old pics for congenital cases

what is the CHP?

eye is excyclo - headtilt AWAY from affected side
eye is HYPER - chin depression gets away from depression
face turn away from affected side

what muscle would you differentially diagnose from a SO?

SR vs SO

BHTT = differentiating 4th CNP from other vertical deviations

min 4 dioptre difference

what is the maximum position of action of the SO?

depression in adduction

describe 4 steps of muscle sequelae

1) primary u/a muscle
2) o/a of contralateral synergist
3) u/a or contracture of ipsilateral antagonist
4) o/a or secondary inhibition of contralateral antagonist

what would you expect to see on measurements at N and D for a 4th NP?

bigger at N>D

what is step 1 in the BHTT?

which is the higher eye?
reduces possible muscles to 4 muscles

pathway

origin

Ventral part of the periaqueductal grey of the midbrain.

• level of inferior colliculus

• Fibres emerge and pass dorsally around periaqueductal grey

• Fibers cross in the midline

• Fibres exit dorsal midbrain

• In sucharachnoid space

• Nerve passes around cerebral peduncle

• Passes between posterior cerebral and superior cerebellar arteries

• Pierces the dura at tentorium cerebelli.

• Enters cavernous sinus - lies in lateral wall

• Enters the orbit via Superior Ortbital Fissure

• supplies SO

location of lesion + cong/ acquired

• lesion in nucleus or fasicular lesion of midbrain

• susceptible to damage as exit midbrain & vulnerable to CS & orbital apex

• congenital or acquired

Congenital

• tendon is lax and long

acquired

• trauma - bilateral as 4th arise from dorsal aspect of midbrain - long route- susceptible to injury

• vascular - hypertension

• diabetes

• SOL

inv

CH

• congenital

  • bilateral

  • manifest strabismus without binocular function

  • binocular function - but AHP

  • symptoms of decompensation when pt was BV w AHP - but difficult to control dev - dip, headaches and asthenopia

  • older pts

  • facial asymmetry

• acquired

  • unilat

  • bilat - closed head trauma

  • symptoms - cyclovertical dip - worse in down gaze

  • AHP - long standing dev

• AHP

  • unilat - chin depression FT and head tilt away from affected side

  • bilat - chin depression - no FT or head tilt unless 1 side affected more than other

• CT

  • c & s AHP

  • c - latent

  • s - manifest

  • affected eye - HyperT - N>D

    • eso dev

• OM

• u/a in pp SO

  • o/a contralateral IR

  • o/a ipsilateral IO

  • u/a SR secondary

• bilateral

  • V pattern

• knapps

• poor elevation & depresssion in adduction of ipsilateral eye = injury to SO = muscle restriction & paresis

INV continue

convergence

• reduced due to CI or vertical dev

correct dev see if conv improves

BV

• C & S AHP

• no BSV in bilateral

• congenital - sm bsv

Hess chart

FOF

• area of bsv is displaced upward to affected side

Diplopia

• N test looking down

• dip is vertical and uncrossed

• if exo - H element of dip crossed

BHHT

• CT in pp - head straight - HYper in affected eye

• if positive - ↑ in affected side

• unaffected side ↓

Torsion

• excyclotorisoin in bilateral

Prism

• temporary correct angle and AHP

Difference in SO and SR

SO

CT

• Hyper dev if fixing w unaffected eye

• dev N>

AHP

• chin depression

OM

• ↑ angle on depression

Hess chart

• ↑ -ve displacement on depression

extorsion

• common

BHTT

• +VE

SR

CT

• Hypo if fixing w unaffected eye

• dev ↑ D>

AHP

• chin elevation

OM

• ↑ angle in elevation

Hess

• ↑-ve in elevation

extorsion

• rare

BHTT

• -ve

differences in bilat/unilat SO palsy

unilateral

CT - hyperT dev in pp - reflect extent of palsy

OM - no reversal of hyperT and dip on lateral versions

• slight V

AHP - chin depP = head tilt + turn

torsion - slight extorsion

BHTT - +ve to affected side

bilateral

CT - sl hyper dev in pp

OM

• reversal of hyperT and dip on lateral versions

• large V

AHP - chin depression

Extorsion - > 10^ - Mrkd Torsion

BHTT - +ve w head tilt to either shoulder

mx- congenital

Correct refractive error.

• Treat amblyopia if present.

Surgical Indications:

• Strabismus.

• Marked abnormal head posture.

• Decompensating cases with moderate/large-angle deviations.

Surgical Options:

• SO tuck (for abnormal superior oblique tendons).

• Weaken overacting muscles:

  • Inferior oblique.

  • Inferior rectus.

• adjustable sutures

mx - acquired

• Treat underlying cause (e.g. hypertension).

• Spontaneous recovery common within 3–6 months.

Non-surgical Options:

• Prisms - <10 - after 6m stab;e

• Occlusion:

  • Temporary relief from diplopia during observation period.

• Botulinum toxin:

  • inferior oblique to reduce hypertropia.

So myokomia

Definition & Features:

• Rare, benign, self-limiting disorder.

• Typically unilateral.

• May follow acquired superior oblique palsy.

• Visible under slit lamp or ophthalmoscope.

• Symptoms include:

  • Intermittent oscillopsia.

  • Torsional monocular diplopia.

Causes:

• Often idiopathic.

  • Nerve compression by blood vessels in posterior fossa.

• Rare associations: multiple sclerosis, space-occupying lesions, dural AV fistula.

• Neuroimaging recommended to rule out serious pathology.

Management:

• Carbamazepine (Tegretol) often effective:

• Alternatives: propranolol, gabapentin.

• Surgery (rarely curative, for severe cases):

  • Superior oblique intrasheath tenotomy / nasal tenectomy.

  • May combine with inferior oblique recession/myectomy.

  • Other options: Harada–Ito, trochlea resection after failed initial surgery.

Why does 4th cnp head tilt away from affected side

E.g RSO affected

Head tilt to left as SO incyclo and depresses

So not working its going to excyclo and hypert elevate

So moving to left its going to work on unaffected muscle e.g. L SR which 3rd action is to inclyclo to compensate for the excyclo of RSO

DD

DD

• TED

• ocular surgery

• skew deviation

  • incyclo in skew - suprine test resolves

  • excyclo in 4th

• 3rd CNP

• MG

• decompensated hyperphoria

• orbital fracture

• childhood strabismus

sx

Surgical Options (after ≥6 months of stability):

• If inferior oblique overacts → Recession.

• If superior rectus restricted → Recession.

• If superior oblique lax → Tuck.

• >15 prism dioptres deviation → Consider multiple muscle surgery:

  • Ipsilateral inferior oblique + superior rectus recession.

  • Ipsilateral superior oblique tuck.

  • Contralateral inferior rectus recession.

• Combined vertical + horizontal deviations:

  • Surgery on both planes if horizontal >8 prism dioptres.

• Use of adjustable sutures may improve outcomes.

Sx

-          Unilateral

o    SO tuck

o    IO weakening

-          Bilat

o    Bilateral SO tuck

o    Harada ito =torsion

longstanding or acquired

Longstanding or acquired

o    VFR

o    Mx torsion – congenital 4^ths no torsion due to retinal reorientation

o    AHP – LS

clinical presen

-          Diplopia: vertical + subjective torsion

o    Worse in downgaze

-          CHP

o    Eye: excyclo + HyperT

o    Head tilt: away from affected side

o    Chin: depressed

o   FT: away from affected side

Further tests

o    Blood test

o    Blood pressure

o    MRI