Altered mental status / encephalopathy — imaging triage
Recommended: CT head without contrast is the preferred imaging study for altered mental status / encephalopathy — imaging triage. Non-contrast CT head first — excludes bleed, mass effect, hydrocephalus, large infarct.
Recommended study
CT head without contrast
Non-contrast CT head first — excludes bleed, mass effect, hydrocephalus, large infarct. If CT is unremarkable and AMS persists, MRI brain (DWI + FLAIR) covers acute infarct, encephalitis, PRES, autoimmune etiologies. MRA / CTA when vascular cause is considered.
If the default doesn't apply
Encephalitis / autoimmune suspected
MRI
MRI brain with and without contrast (see encephalitis, autoimmune-encephalitis)
IV contrast
Stroke-like presentation
CT
Stroke protocol — CT/CTA/CTP (see stroke-acute)
IV contrast
Seizure-related (post-ictal AMS)
MRI
MRI brain (see seizure-first, status-epilepticus)
IV contrast
Hypertensive emergency + AMS
MRI
MRI brain — look for PRES (see pres)
No contrast
Suspected hydrocephalus
CT
CT head; MRI for cause characterization (see acute-hydrocephalus, nph)
No contrast
Watch-outs
Metabolic / toxic encephalopathy
Imaging is typically unremarkable — don't keep scanning. Focus on labs; consider EEG.
Wernicke encephalopathy
MRI: symmetric T2/FLAIR hyperintensity in mammillary bodies, periaqueductal grey, medial thalami — treat with thiamine before confirming.
Pearls
- DWI is the highest-yield sequence in unexplained AMS — catches acute infarct and HSV encephalitis.
- Bilateral basal ganglia / thalamic signal change has a tight differential: CO poisoning, hypoxia, Wilson's, CJD, osmotic.
- PRES vs RCVS: PRES has parieto-occipital vasogenic edema; RCVS has segmental vasoconstriction on angiography.