USMLE Forums banner

1 - 10 of 10 Posts

·
Ex-USMLE Forums Staff
Joined
·
753 Posts
Discussion Starter #1
45 year old male presented with headache and double vision. On examination you noticed that the patient is unable to look to the left in both eyes. Some facial muscle weakness also noted. Which of the following labeled structures is the most likely site of the lesion.

brainstemlesion.JPG
 

·
Registered
Joined
·
37 Posts
45 year old male presented with headache and double vision. On examination you noticed that the patient is unable to look to the left in both eyes. Some facial muscle weakness also noted. Which of the following labeled structures is the most likely site of the lesion.

View attachment 374
is the lesion at D? bcs in the clinical vignette, pt exhibits c/f s/o 6th nv palsy (being unable to look to the left and c/o diplopia) and 7th nerve palsy (facial weakness). so the only answer i think is logical in this case, is at the facial colliculus namely D.
 

·
Ex-USMLE Forums Staff
Joined
·
753 Posts
Discussion Starter #5
Correct Answer

The correct answer is D.

The clue to the answer is that both eyes failed to go to the left. Which means paralysis of left lateral rectus and right medial rectus. So this cannot be lesion of the abducens nerve alone (labeled F in the diagram) as it supplies the lateral rectus only.

It must be paralysis of the conjugate gaze pathway.

Lesions of abducens nerve nucleus causes ipsilateral loss of abduction and contralateral (via medial longitudinal fasciculus MLF) loss of adduction. A lesion of the paramedian pontine reticular formation (PPRF) also causes similar gaze palsy.

Looking at the diagram above you can see the facial nerve root arches over the abducens nucleus (genu of facial nerve) before it exits from the lateral surface of the pons (labeled G in diagram). Therefore, a lesion of the abducens nerve nucleus frequently affects these fibers also, and may cause various degrees of facial muscle weakness.
 

·
Registered
Joined
·
281 Posts
BUT D in this diagram is the sixth nerve nuclei and then how can it be a MLF lesion????:notsure:
 

·
Registered
Joined
·
3,263 Posts
BUT D in this diagram is the sixth nerve nuclei and then how can it be a MLF lesion????:notsure:
The control of conjugate gaze is mediated in the brainstem by the medial longitudinal fasciculus (MLF), a nerve tract that connects the three extraocular motor nuclei (abducens, trochlear and oculomotor) into a single functional unit. Lesions of the abducens nucleus and the MLF produce observable sixth nerve problems, most notably internuclear ophthalmoplegia (INO).

-
 

·
Registered
Joined
·
281 Posts
The control of conjugate gaze is mediated in the brainstem by the medial longitudinal fasciculus (MLF), a nerve tract that connects the three extraocular motor nuclei (abducens, trochlear and oculomotor) into a single functional unit. Lesions of the abducens nucleus and the MLF produce observable sixth nerve problems, most notably internuclear ophthalmoplegia (INO).

-
Does that mean Abducens ,trochlea or oculomotor lesion will present same as a MLF lesion with internuclear ophthamoplegia?
 

·
Registered
Joined
·
13 Posts
Just clearing things up...

I suppose this question isn't supposed to be taken as a "textbook definition" of MLF syndrome/INO, because we'd be assuming that the lesion in the pt would be due to a lesion in the (right) MLF alone...

Instead we're considering the consequences of damaging the abducens nucleus (presumably on the left), in which case the left eye can't look left, and then via the right MLF, the right eye can't look left either.

Is this correct?
 
1 - 10 of 10 Posts
Top