Hit on the head question

[lsu1000]

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A man is hit on the back of the head with a 2 x 4 and injures his optic circuit. What defect will be seen?

A. bitemporal hemianopsia
B. down and out
C. up and out
D. blindness

 

[Wrigleyville]

A man is hit on the back of the head with a 2 x 4 and injures his optic circuit. What defect will be seen?

A. bitemporal hemianopsia
B. down and out
C. up and out
D. blindness

I'm not sure what you mean by an optic circuit. A circuit is a complete pathway, like the pupillary light reflex, w/ afferent and efferent limbs. Do you mean the visual cortex in the occipital lobe? Damage to that would cause visual field defects, or blindness if it was extensive.

 

[Idiopathic]

I think by down and out, etc. you are referring to the motion of the eye when the superior oblique, etc. are engaged? The only answer that makes sense here is d) blindness. The visual cortices are at the posterior brain, while bitemporal hemianopsia is seen when something compresses on the optic chiasm (i.e. pituitary tumor). The other two cases could be seen with injury to one of the crania nerves, cavernous sinous thrombus, etc.

 

[lsu1000]

The question I had, said he was hit on the back of the head and then the answers listed were those pictures that show the darkened areas of visual field defects. It listed several of them, but now remembering back I don't think it even listed the total blindness.

I thought maybe there was an obvious answer for someone hit in the back of the head and his immediate visual field defect...maybe not.

Sorry for the confusion on the original post 😉

 

[Idiopathic]

The question I had, said he was hit on the back of the head and then the answers listed were those pictures that show the darkened areas of visual field defects. It listed several of them, but now remembering back I don't think it even listed the total blindness.

I thought maybe there was an obvious answer for someone hit in the back of the head and his immediate visual field defect...maybe not.

Sorry for the confusion on the original post 😉

Maybe he was hit on the left or right side? Otherwise, remember that part of the visual field runs parietal->occipital while other other half (Meyer's loop) goes out into the temporal region. So a blow to the top of the head miight do different damage than a blow to the back. Also, if the visiual cortices are knocked off you can get some central vision sparing.

 

[InHoc]

Maybe he was hit on the left or right side? Otherwise, remember that part of the visual field runs parietal->occipital while other other half (Meyer's loop) goes out into the temporal region. So a blow to the top of the head miight do different damage than a blow to the back. Also, if the visiual cortices are knocked off you can get some central vision sparing.

on that note, i've never understood why there is central sparing - is the central visual field's message received or routed to somewhere unique?

 

[Radiohead]

I believe the answer would be "up and out", or the "pie in the sky" distribution. I believe the technical term is a bitemporal superior quadrantanopsia, due to a hit in the optic radiation. I don't think it is talking about EOM's.

 

[BlackNDecker]

on that note, i've never understood why there is central sparing - is the central visual field's message received or routed to somewhere unique?

Central sparing is the result of dual supply to the Primary Visual Cortex. Remember that the anterior bank of the calcarine sulcus contains everthing but the central 10-15% of the visual field, the central visual field is on the posterior portion(and comprises a much larger share of) the calcarine sulcus. I don't exactly recall the supply to the peripheral and central fields...P4 & P5 to peripheral fields...hmmm...I'll have to get back on this one.

 

[kreddy]

The MCA & PCA converge (watershed) on 17a. So 17a has dual supply, but primarily PCA(P4/P5). The concept of macular sparing is somewhat clinically irrelevant from what I gather from clinicians, because most people with lesions of the primary visual cortex also have some degree of "eye wander" and the central 10-15% of visual field is very hard to analyze in this situation. Additionally, central sparing may also result from incomplete infarction of 17a. That is, the smaller/deeper penetrating branches to the anterior(peripheral vision) portion of 17a, with patency of vessels supplying posterior(central visual field) portion of 17a.

This is how I learned the concept...please feel free to correct.

 

[Ramoray]

dude if a question as vague as that can be askedon step 1 id be pissed... " a guy gets hit on the back of the head" what happens.. come on, a multitude of **** could happen, he coudl have a hematoma compressing the right or left side, the upper or lower, he could have hit it on the left or right back head... god that just CANT be a good question

 

[Pox in a box]

dude if a question as vague as that can be askedon step 1 id be pissed... " a guy gets hit on the back of the head" what happens.. come on, a multitude of **** could happen, he coudl have a hematoma compressing the right or left side, the upper or lower, he could have hit it on the left or right back head... god that just CANT be a good question

I agree with your Ramoray. This question is ridiculously oversimplified.

 

[me454555]

Hit on the back of the head = hemianopia w/macular sparing

 

[BlackNDecker]

Hit on the back of the head = hemianopia w/macular sparing

That is not an answer option...see first post in thread.

 

[lsu1000]

Was on my May 26th exam.

 

[BlackNDecker]

Was on my May 26th exam.

Isu1000, are you responding to me? B/C ME454555's answer was not one that you listed....you didn't list macular sparing as a choice.

 

[lsu1000]

I was just letting people know that this was in fact a question. It had choices like A-J so I'm sure mac degeneration was on there. But I had no clue.

 

[Ramoray]

well than i guess i was wrong, and you do see vague questions. Just from all the nbme shelfs i took, i never saw a bad question once in any of the subjects and thought they were all high quality questions. This sounds like a question my prof would ask in our neuro class. If you had to c hoose from those i think if you hit a guy on the back of the center of the head which i think the question implies than no doubts its total blndness, your visual cortex is right there, you hit that, your sight is gone, no questions. I think for the other choices you would need to atleast hint at either a top or bottom of the head blow or right or left back blow but just back to me equals blindess. Why would you have macular sparing? when you hit the cortex directly it doesn tmatter how well supplied the macular region is with blood, .. if you hit the visual cortex with the macular area, your vision is gone inccluding macula. Macular sparing is more important with strokes of the PCA because you spare the macual due to its 2nd blood supply from MCA. It has no baring when you directly injure the cortex]

 

[Janders]

hemianopic paracentral scotoma:
-lesion at posterior segment of occipital lobe
-etiology blunt trauma or severe hypotension (watershed area)

 

[Pox in a box]

well than i guess i was wrong, and you do see vague questions. Just from all the nbme shelfs i took, i never saw a bad question once in any of the subjects and thought they were all high quality questions. This sounds like a question my prof would ask in our neuro class. If you had to c hoose from those i think if you hit a guy on the back of the center of the head which i think the question implies than no doubts its total blndness, your visual cortex is right there, you hit that, your sight is gone, no questions. I think for the other choices you would need to atleast hint at either a top or bottom of the head blow or right or left back blow but just back to me equals blindess. Why would you have macular sparing? when you hit the cortex directly it doesn tmatter how well supplied the macular region is with blood, .. if you hit the visual cortex with the macular area, your vision is gone inccluding macula. Macular sparing is more important with strokes of the PCA because you spare the macual due to its 2nd blood supply from MCA. It has no baring when you directly injure the cortex]

Ramoray, I respectfully want to give you some advice. Stop wasting time discussing stupid details that even you yourself would call stupid in retrospect. This type of question is not high yield for USMLE. It's too generic and there's just memory here. You have to be able to apply the information they give you and hone on the things you've learned. I don't want to see you on here right before your exam saying you ran out of time because you've spent hours typing up rebuttals to questions that most people who've taken the exam would regard as stupid.

 

[Ramoray]

Ramoray, I respectfully want to give you some advice. Stop wasting time discussing stupid details that even you yourself would call stupid in retrospect. This type of question is not high yield for USMLE. It's too generic and there's just memory here. You have to be able to apply the information they give you and hone on the things you've learned. I don't want to see you on here right before your exam saying you ran out of time because you've spent hours typing up rebuttals to questions that most people who've taken the exam would regard as stupid.

ha thanks pox your right im gonna write down these wise words fo yours and read them to remember not to waste time with small useless dumb questions. your a smart person, very wise! thanks for the kick in the butt

 

[Pox in a box]

ha thanks pox your right im gonna write down these wise words fo yours and read them to remember not to waste time with small useless dumb questions. your a smart person, very wise! thanks for the kick in the butt

No problem. Now get back in there and study. You can continue to add tools to your toolbox later.

 

[HiddenTruth]

No problem. Now get back in there and study. You can continue to add tools to your toolbox later.

well said! Ram's toolbox gets bigger each day!