This most classical of all Neurointensive-care-topic is – in my eyes – not only very important, but also quite hard to understand. If you belive Plum/Posner, it alls seems quite simple, but the details are often wrong. This starts with the reason for pupil dilatation in tentorial herniation (there are at least 3 different ways to achieve it and sometimes more than one applies), it goes on with the role of midline shift, the horizontal and vertical displacement and so on.
Here are my core teaching messages:
- The third nerve runs between the SCA and PCA.
- Inspect your CT completely, thinking about pressure and tissue shifts. Look at the midline, the mesencephalon, the third nerve, the pyramidal tract, the ARAS, the thalami, the uncus, the falx etc. Look everywhere.
- Midline shift is (in stroke and ICH) irrelevant, if nothing else happens.
- Pupils and drowsiness need not happen together.
- Think about why the pupils dilate, the pt is drowsy, he vomits in each patient. The mechanism can be different each time.
- Operation only helps if it heals the pathological mechanism.