The Tobey Ayer test is for a block in the spinal canal.
Pressure is applied to the neck in order to compress the internal jugular veins; this reduces venous outflow from the cranium and raises the intracranial pressure. A spinal puncture will displace CSF into the spinal sac and cause the measured CSF pressure, e.g. by manometer, to rise rapidly. This is not seen if a spinal block to the flow of CSF is present, as in Froin's syndrome.
The test is very unreliable.
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