4th cranial nerve

what is 4th nerve name?

trochlear nerve

supplies SO

incyclorotation, depression, abduction

where is the 4th nerve nuclei located?

caudal end of 3rd nerve nucleus and dorsal aspect of midbrain

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

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

inflammation
ischaemia
infiltration
compression
trauma

describe the diplopia in a 4th CNP

vertical, may have subjective torsional

would diplopia be present in acquired or congenital cases?

can be both, congenital longstanding decompensating 4th CNP common

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

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 the Bielschowsky head tilt test (BHTT) used for?

differentiating 4th CNP from other vertical deviations

what happens in the BHTT when the patients head is tilted to the affected side?

increase in vertical deviations in a 4th CNP

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