4th cranial nerve

ANATOMY & CLINICAL SIGNIFICANCE OF 4TH

CRANIAL NERVE

Dr.Ashok Kumar Valuroutu

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TROCHLEAR NERVE


FUNCTIONAL COMPONENTS

• SOMATIC EFFERENT-concerned with movement of eye ball through SO.

• GENERAL SOMATIC AFFERENT-carries proprioceptive impulses from SO which are relayed in the mesencephalic nucleus of 5 th nerve.


COURSE AND DISTRIBUTION

1)Fascicular part

2)Pre cavernous part

3)Intra cavernous part

4)Intra orbital part


• SITUATION: at the level of inferior colliculus in the ventromedial part of central gray metter of midbrain dorsal to medial longitudinal bundle.

• Caudal & continous with 3rd nucleus complex.


FASCICULAR PART:

• axons leave the nucleus

• curve posteriorly around the aquiduct in the central greymatter

• decussate in the anterior medullary velum.


PRECAVERNOUS PART: leaves the brainstem on the dorsal surface

just caudal to inferior colliculus winds around brainstem runs forwards beneath the free edge of

tentorium pierces the dura on the posterior corner of

the roof of cavernous sinus to enter in to it.


INTRACAVERNOUS PART:

Runs forwards in the lateral wall of the sinus,lying below 3rd nerve and above the 1st division of 5th nerve.

In the anterior part of the sinus, it rises,

crosses over the 3rd nerve

passes through the superior orbital fissure, above and lateral to annulus of zinn.


INTRA ORBITITAL PART:

• Enters the orbit through lateral part of SOF

• Frontal & lacrimal nerves laterally, ophthalmic vein inferiorly.

• Divides in to fan shaped manner into 3 or 4 branches

• Ends by supplying SO on its orbital surface near lateral border.


CONNECTIONS:

1)Cerebral cortex

Motor cortex - cortico nuclear tracts

Visual cortex - supeior colliculus & tactobulbar Frontal eye field. tracts.

2)Nuclei of 3rd ,6th&8th -MLF

3)Superior colliculi -descending predorsal bundle

4)Vertical & torsional gaze centres

5)Cerebellum - vestibular nuclei.


UNIQUE CHARACTERS

• Only cranial nerve to emerge from dorsal aspect of brain.

• Only crossed cranial nerve

• Longest Intra cranial course(about 75 mm)& thinnest of all cranial nerves


CLINICAL FEATURESSYMPTOMS:• Ac.onset of double vision,• Difficulty in going downstairs,• VertigoSIGNS: • Hyperdeviation ,limitation of depression in adduction,• Extorsion, vertical diplopia,• Hypertropia on opposite gaze• Charecteristic head posture- head tilted to opposite side face turned towards opposite side chin depressed


SPECIAL TESTS


PARK’S 3 STEP TEST:

STEP 1: Identify the HYPERTROPIC EYE in primary position.

depressors of hypertropic eye- SO,IR.

elevators of hypotropic eye-SR,IO.

STEP 2: Determine whether hypertropia is greater in Rt or Lt gaze.

on Lt gaze Lt SR, Rt.SO

on Rt gaze Rt IR, Lt IO


STEP 3: Tilt the head towards each shoulder, look for vertical sqint.

BEILSCHOWSKY HEAD TILT TEST: same principle as the 3rd step of PARK TEST Pt fixates, head tilted Rt &Lt of Lt hypertropia on Lt head tilt- Lt SO of Lt hypertropia on Rt head tilt- Lt IR


DOUBLE MADDOX ROD TEST :

For measuring the degree of cyclodeviation.

In unilateral palsy – cyclodeviation <10 deg

In bilateral palsy – cyclodeviation >10 deg


Differential Diagnosis of Vertical Binocular Diplopia• Superior Oblique Palsy• Thyroid Ophthalmopathy• Myasthenia Gravis• Brown Syndrome• Orbital fracture with entrapment• Cyclovertical paresis or overaction• Skew Deviation/Ocular Tilt• Dissociated Vertical Deviation


Isolated Superior Oblique Palsy

• Most common etiologies are congenital and traumatic

• Also vascular; less commonly tumor, demyelinating

• In absence of other neurological symptoms and presence of vascular risk factors, reasonable to observe


TREATMENT• CONGENITAL:large hypertropia in PP treated by

SO tucking• ACQUIRED:

SMALL- ipsilateral IO weakening.

MODERATE- ipsilateral IO weakening with ipsilateral SR weakening .

PURE EXCYCLOTROPIA: without hypertropia –HARADA- Ito procedure

Splitting & ALT OF lateral half of SO tendon.

4th cranial nerve

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