Hello and thank you for your question.
If one had a direct blow to the head and had shunt due to hydrocephalus it can be dangerous.
One can get seizures, hemorrhage, CSF hypotensive headaches, cerebral infarct, shunt occlusion, catheter breakage and even infection.
if you have headaches, feel dizzy, nauseous, sleepy or lethargic than you should seek immediate medical attention.
You also need to consult your neurosurgeon to evaluate if you need shunt revision or not.
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One more question. Could a blow potentially be fatal? I am concerned for my son, who may soon be put in a very volatile situation