docswapna
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An 60-year-old man suffers from severe hypoxia with resulting severe brain edema. This edema leads to raised intracranial pressure. When the pressure exceeds 200 mmHg, the medial temporal lobe begins to be compressed against the tentorium cerebelli. What is typically the first sign of such compression?
A. Anisocoria contralateral to compression
B. Anisocoria ipsilateral to compression
C. Both pupils 5–6 mm and fixed
D. External oculomotor ophthalmoplegia
E. This condition has no effect on the eyes
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| hope99
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C uncal herniation ?
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| dranrop
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ya , the ans is c
fixed dilated pupils
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| dranrop
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sorry
i think d ans is anisocoria on ipsilateral side....fixed dilated pupil on ipsilateral side
Uncal herniation
In uncal or transtentorial herniation, the innermost part of the temporal lobe, the uncus, can be squeezed so much that it goes by the tentorium and puts pressure on the brainstem (Shepherd, 2004). The tentorium is a structure within the skull formed by the meningeal layer the dura mater. Tissue may be stripped from the cerebral cortex in a process called decortication (McCaffrey, 2001). The uncus can squeeze the third cranial nerve, which controls parasympathetic input to the eye on the side of the affected nerve. This interrupts the parasympathetic neural transmission, causing the pupil of the affected eye to dilate and fail to constrict in response to light as it should, so a dilated unresponsive pupil is an important sign of increased intracranial pressure (Cornell, 1998). Cranial arteries may be compressed during the herniation (Orlando Regional Healthcare, 2004). This type of herniation can also damage the brain stem, causing lethargy, slow heart rate, respiratory abnormalities, and pupil dilation (McCaffrey, 2001). Uncal herniation may advance to central herniation
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| IceAge
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as dranrop said ..... parasym fib are on the outside on CN 3. therefore the first sign of compression is ipsi dil of pupils .... followed by (f/b) ..... complete CN3 paralysis .... f/b .... contralat CN3 compression leading to bil dil pupils
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| docarchana
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i guess its B.
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| lam79m
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That would cause anisocoria, so b and d correct
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| sridevibandaru24
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B
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| Dr.Papez
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Anisocoria means unequal pupils...doesnt say which one is large or small.
So the options a and b are technically wrong.
Usually becos of uncal herniation, pupillomotor fibers get compressed first (they are the outermost in the 3rd nerve fasicle...leadin to transient ipsilateral pupillar constriction (due to irritation-usually un noticed and not emphasised often) later leading to pupillary paralysis-dilated non/less reactive pupil. rarely one can have contralateral pupil involvement earlier also, especially if a large lesion is very much away from uncus (say parieat or high frontal) shifting the whole hemisphere (and midbrain) to opp side and the opp 3rd nevre get compressed. (confusing?)
the Q stem says 200 mmg Hg intr cranial pressure-this will guarantee instant brain death as it is very much above usualy systolic pressure-probably it was meant to be just 20 mm Hg.
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| docsrinu
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thanku Dr.papez
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| docswapna
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so is ur ans C, drpapez..
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| Dr.Papez
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if the pressure is 200, damn sure... it will be dilated pupils both sides.
But such complicate stuff is usually not tested in USMLE. think simple but scientifically that is it.
I dont want to choose among the options in the stem. Let us learn the concept
In majority of cases with uncal herniation, ipsilateral pupillary dilatation is the usual sign.
Hope that helps.
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