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NBME 24 Answers

nbme24/Block 4/Question#17 (42.7 difficulty score)
A 63-year-old woman undergoes operative ...
Decreased movement through the arachnoid villi🔍
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 +12  upvote downvote
submitted by happysingh(34),

so, the Key words that no one is mentioning : communicating hydrocephalus

the pathophys goes like this :

an inflammatory setting (i.e., subarachnoid hemorrhage) yield fibrosis / scarring of the arachnoid granulations => impaired CSF drainage

the key points / concepts they are trying to test here : 1. do you know what communicating hydrocephalus (without them telling you those words) 2. do you know what's the pathophysiology (of communicating hydrocephalus) is ?

potentialdoctor1  Exactly. To add to this, communicating hydrocephalus can be subdivided as follows: Normal-pressure hydrocephalus: Chronic/gradual decrease in CSF reabsorption at arachnoid granulations, usually due to calcification due to aging. CSF accumulates slowly, so ventricles are able to widen without causing an important increase in intracranial pressure. Symptoms occur due to compression of periventricular white matter tracts ---> Wacky, wobbly, wet High-pressure hydrocephalus: Acute decrease in CSF reabsorption at arachnoid granulations, usually due to inflammatory state in the subarachnoid space (eg, meningitis, sub-arachnoid hemorrhage). CSF accumulates suddenly, causing an acute-onset increase in intracranial pressure +6  
sunshinesweetheart  not to take away from your perfect explanations, but if it were a woman with neck stiffness and fever (rather than circle of willis rupture) that could lead to increased CSF production, right? I think that's the only case where CSF production would increase. Also I think decr absorption in arachnoid granulations in that situation as well so it'd be a shit question +  
peqmd  If anyone like me also got "decreased absorption in choroid plexus", as their wrong answer it's because the choroid plexus doesn't "absorb" it produces. +5  
alienfever  FA 19 p510 +1  
alienfever  If anyone chose F, communication hydrocephalus is caused by decreased absorption and not increased production. FA 19 p510. +  



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keycompany  Also take into account this patient had surgery that requires penetration into the subarachnoid space (hence through the arachnoid mater). This can lead to scarring of the arachnoid granulations and subsequent communicating hydrocephalus. +9  



 +2  upvote downvote
submitted by roygbiv(17),
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zbird  So this patient has a leaking berry aneurysm which undergone to surgery and repaired but in two days she developed widening of the SA space which could be explained by increased CSF production but a decreased in absorption, which is due to blockage of the arachinoid granulations by the leaked red and white cells therefore there is a decreased movement of the CSF via the arachinoid villi +1  



 +2  upvote downvote
submitted by krewfoo99(75),

Why would decreased movement through the cerebreal aquaduct be wrong? With all the build of blood in the CSF tract without absorption, wouldnt movement also be decreased through the aqueduct?

ergogenic22  this would cause a non-communicating hydrocephalus with enlarging of the lateral and 3rd ventricles but normal 4th ventricle and subarachnoid space +1  



 +2  upvote downvote
submitted by diabetes(15),

simply the blood inside the CSF become blocked through arachnoid granulations ==> decrease absorption of CSF==>communicating hydrocephalus.