Table 1

Caveats for interpreting ‘normal’ imaging

DiagnosisRisks of missing the diagnosis
Subarachnoid haemorrhage (SAH)Although only ∼2% of SAH patients SAH have a normal CT head scan initially, there are risks with a missed diagnosis: case fatality rate ∼50% and mean medicolegal cost of a claim for damages in SAH in the UK stands ∼£211 00022
Ischaemic strokePlain film CT scan can be normal in initial stages, posterior circulation strokes are difficult to visualise on CT
Idiopathic intracranial hypertensionImaging normal but potential for irreversible sight loss if not managed appropriately2
Neuromuscular disordersInitial presentation of both myasthenia gravis and Guillain–Barré syndrome may (in early phases) be misdiagnosed as a brain stem stroke or possible cord compression (mortality rate of 8.7 and 7.7% respectively in those patients requiring intensive care23)
Functional disordersRisk is from delayed diagnosis, over-investigation and iatrogenic harm24