Perhaps the more worrisome contraindication to lumbar puncture is the suspicion of increased intracranial pressure (ICP) due to a cerebral mass lesion. In the presence of a potential brain tumor, cerebral hemorrhage, cavernous sinus thrombosis, brain abscesses, epidural or subdural hematomas , patients are at increased risk of deteriorating neurologically with LP. As the space-occupying lesion grows, ICP rises. When lumbar puncture is performed in these patients, a low-pressure shunt is formed at the site of LP where CSF can escape. As the CSF pressure drops in the spinal column, CSF and brain mass may then shift towards the low-pressure outlet (the LP site). This may lead to either trans-tentorial or uncal herniation and acute neurological deterioration. Patients with increased ICP from mass lesions often display decreased levels of consciousness, focal neurological signs or papilledema on physical exam. Any of these findings make lumbar puncture contraindicated until further evaluation can be undertaken.
LP is contraindicated in cases where there is compartmentalized increased intracranial pressure. If there is a pressure gradient either between lumbar space and the posterior fossa; or between the lumbar space and the supratentorial compartment, withdrawal of CSF can lower the pressure in the lumbar space, increase the pressure gradient, and potentially lead to herniation and death.
If there is IIH it is not dangerous to perform because the pressure is all uniform.
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