Neuroimaging, Neuromonitoring, and Brain Death
Imaging and monitoring
Know when to use CT (hemorrhage, herniation, hydrocephalus), MRI (ischemia, infection, demyelination), and vascular imaging (CTA/MRA/DSA). Understand the significance of midline shift, herniation signs (effaced cisterns, uncal herniation), and the limitations of early CT in ischemia. Neuromonitoring includes ICP, EEG, transcranial Doppler, and near-infrared spectroscopy - each with strengths and pitfalls.
Brain death
Brain death is the irreversible cessation of all brain function, including the brainstem, with a known cause and exclusion of confounders (sedation, hypothermia, metabolic derangement, neuromuscular blockade). The clinical exam includes coma, absent brainstem reflexes, and apnea testing. Ancillary testing (EEG, cerebral angiography, radionuclide) is used when the clinical exam cannot be completed. Understand the apnea test procedure and its pitfalls (hypoxia, hypotension, false results).
Traps
- Declaring brain death without excluding confounders.
- Misinterpreting an apnea test done with inadequate preoxygenation or unstable hemodynamics.
- Relying on a single imaging modality when the clinical exam is definitive or vice versa.
Rule of thumb
Brain death requires: known cause + excluded confounders + clinical exam (or validated ancillary test).
Worked example
A comatose patient on propofol with absent reflexes - do not declare brain death until the drug is cleared and confounders excluded; repeat the exam after an appropriate interval.