How can ct/x-ray determine blockage of a vp shunt in intracranial hypertension (not hydrocephalus ) there is no change in ventricle sizing in iih?

It can't: X-rays and ct can not determine shunt blockage. There are no perfect tests to detect that. The most reliable are shunt tap or nuclear shuntogram.

Swelling: Ct can look for increased edema (swelling) of the brain. The xray looks at the shuntitself to make sure nothing has come apart or kinked in the tubing.

They can't: A shunt blockage will not show on either ct or xrays. Useful methods to assess for blockage include 1. Radionucleotide shunt study 2. Shunt interrogation by your neurosurgeon, or 3. Dilated ophthalmological exam to check for papilledema. If in doubt circle back with your neurosurgeon.

Radiographs may be .: Taken to see if the shunt tubing is patent - ie, not broken or disconnected along its course. Also, head ct could show a change in ventricular size - generally bigger if the shunt is not working, compared to a prior ct. However, to "prove" sure the shunt is working, a radionuclide vp shunt study, or interrogating the shunt as directed by the manufacturer may be required. Please see the doc.