99doc
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Cold caloric response in unconscious patient,
1)BRAIN STEM INTACT-eyes deviate towards irrigated side.
2)MLF(BILATERAL)LESION-only the eye tested deviates towards abducted side.
3)LOW BRAIN STEM LESION-no deviation.
can somebody explain all this?
I AM SORRY ABOUT POSTING IT IN THE WRONG FORUM BUT I HAVE ALREADY WRITTEN SO MUCH,SORRY FOR ANY INCONVENIENCE CAUSED.
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| Ms.Apara
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WHT IS THIS BOUT??????? COULD NOT UNDERSTAND
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| Ms.Apara
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it is a caloric test
see ENT book........ ear is irrigated with ice water for 60 sec first with 5 ml if no response than 10 , 20 , 40 ml ...no response dead labyrinth
COWS - nystagmus------ Cold -opposite warm ----same side
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| mesh
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introduction of cold water in the external ear mimics a lesion....cold caloric and warm caloric tests r done to check the integrity of the brain stem....
when u introduce cold water into one ear lets say right..the vestibular nuclei of the right will be inhibited and the nuclei of left side will be unopposed and act as if they r stimulated.so it will turn the eyes in right direction(which occurs due to pathology) and the cortex will move the eyes back to the left(fast component--nystagmus) which occurs as a response to the pathology.
in ur question as far as i can understand it should be option A.....the option is telling bout the slow component which is indeed in the direction of ear tested.....
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| ssrpk
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whta about 2 !
i am thinking VOR should be totally abolished as vestibular nucleus is linked to CNIII/VI via MLF!
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| mesh
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i think the secondary fibres from the vestibular nuclei they join with the MLF fibres and supply the motor nuclei of the respective cranial nerves....
the secondary fibres are responsible for the vestibulo ocular reflex...
even if it is....then how cold caloric test will deviate the tested eye towards abducted side.....in case of bilateral MLF lesion....
plzz xplain..thanks....
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| ssrpk
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first of all wht does tht mean "eyes deviated towards the abducted side"??????
well this is exactly wht i was thinking! there should'nt be any deviation incase of bilateral knockout of MLF!
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| 99doc
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THIS IS NOT A Q.
THIS INFO IS GIVEN IN HY NA.
I DIDNOT GET IT EARLIER BUT AFTER GOING THROUGH KAPLAN'S PATHWAY ON IT I GOT IT.
IT'S A BIT TOO LONG IF U DO'N' GET IT I WILL POST IT FOR U.
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| mesh
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wow... wrong way......
can u xplain the 2 one i didnt really get it....
thanx....
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| ssrpk
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yes please, explain no 2!
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| 99doc
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this info involves both caloric test & the horizontal conjugate gaze.
i guess u have got the others except 2.
so,when we have aBL MLF lesion,as in case of MS,neither eye will adduct as mlf is basically connected to 3rd neve so when a person attempts to look to right side,then right side abducen cause REye to abduct,but the left eye which was supposed to look medially(adduct) will not do so.implies we have only right eye abducted.
IN ATTEMPTED RIGHT GAZE IN NORMAL-
CONTRALATERAL FRONTAL CORTEX EYE FIELD sends to
IPSILATERAL PARAMEDIAN PONTINE RETICULAR FORMATION(PPRF)
IT SENDS TO CONTRALATERAL MLF TO REACH
CONTRALATERAL OCCULOMOTOR
ABDUCENS CAN ACTIVATE ON ITS OWN.
so BL MLF neither left nor right eye can adduct.only right eye on attempt to see to right can adduct so if we irrigate the right ear with cold water in person with this lesion,we end up getting the right eye abducted only.
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| ssrpk
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i think i am mixing things up a bit!
i agree with ur point!
thiung is wht i was asking, how is the vestibular nuclei connected to abducens nuclei?
PPRF is connected to ipsilateral abducens and contralateral oculomotor (via MLF)
sameway vestibular nuclei is connected to ipsilateral oculomotor(via MLF) and contralateral abducens (is'nt this connection provided via MLF?? if it were then bilateral MLF lesion may not affect conjagte gaze in terms of abduction but should totally abolish VOR)
can you clearify this point???
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| 99doc
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This is tough as u say.but this is my view of things-
the vestibular nuclei are indeed connected via MLF to the 3,4&6 nuclei.this is via secondary vestibular fibres which form the efferent limb of VOR.they are responsible for the compensatory eye movements.
wheras the primary fibres deal with vestibular nuclei,vestibular nerve,which innervate the semicircular duct,utricle,saccule.so,when we are irrigating our left ear with cold water then horizontal duct of the left side is inhibited &the body acts as if right side has been stimulated,so the eyes via the primary fibres move towards the left side(slow phase).
now actually there has been no movement of head,so cortex responds by moving eyes back to right side quickly(fast phase-direction of nystagmus).
now this is via the sec. fibres(MLF)there being a lesion of MLF on both sides the ssec fibres don't act but only primary do & we get only slow component to same side of irrigation.
is it ok or i screwed up things.i feel it's soooooo confusing too.but if u keep certain things in mind &go by them i suppose u will get it.
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| mesh
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wat i can get is that...that PPRF supplies with MLF to the contralateral III nerve nuclei only.
PPRF sends its axons to the VI nerve nuclei where it synapses and from here they give rise to the abducens nerve and MLF which goes to the contralateral III nerve nuclei.....
cause its written in kaplan that bilateral MLF lesion neither eye can adduct on attempted gaze and the abducting eye exhibits nystagmus...
hope i am making sense.....
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| ssrpk
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hey guys don't get confused, believe me u are makiong perfect sense of everything, thanks for the exlpanation 99doc 
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| 99doc
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u are welcome
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