Neurological Deficits Warranting CT Head Scan
Any focal neurological deficit on examination mandates immediate CT head imaging, regardless of the clinical context. 1, 2
High-Risk Neurological Deficits Requiring CT Scan
The following neurological deficits meet criteria for emergent CT head imaging:
Focal Neurological Deficits
- Motor weakness (hemiparesis, monoparesis, or any focal weakness) 1, 2
- Sensory deficits (focal numbness, hemisensory loss) 1
- Cranial nerve palsies (facial droop, ophthalmoplegia, visual field defects) 1
- Speech disturbances (aphasia, dysarthria) 1
- Visual field defects (homonymous hemianopia) 1
- Gait ataxia with extracerebellar signs (somnolence, encephalopathy, focal motor weakness) 1
Altered Mental Status with Neurological Features
- Impaired consciousness or unresponsiveness beyond baseline 1, 2
- Deficits in short-term memory following head trauma 1
- Post-traumatic seizure 1
- Glasgow Coma Scale score <15 1
Signs of Elevated Intracranial Pressure
- Papilledema 2
- Cushing's triad (hypertension, bradycardia, irregular respirations) 2
- Progressive neurological deterioration 1
Clinical Context Modifying CT Indication
Head Trauma Scenarios
The 2021 ACR guidelines provide specific algorithms based on loss of consciousness (LOC) and post-traumatic amnesia (PTA): 1
With LOC or PTA - CT indicated if ANY of the following:
- Headache 1
- Vomiting 1
- Age >60 years 1
- Drug or alcohol intoxication 1
- Short-term memory deficits 1
- Physical trauma above clavicles 1
- Coagulopathy (including antiplatelet therapy) 1
Without LOC or PTA - CT should be considered if:
- Age ≥65 years 1
- Severe headache 1
- Physical signs of basilar skull fracture 1
- Dangerous mechanism (ejection from vehicle, pedestrian struck, fall >3 feet or 5 stairs) 1
Altered Mental Status Without Trauma
Risk factors associated with intracranial findings requiring CT: 1
- History of falls 1, 2
- Anticoagulation (warfarin, DOACs) or antiplatelet therapy 1, 2
- Hypertensive emergency 1
- Headache with nausea or vomiting 1
- History of malignancy 1, 2
- Older age with acute change 1, 2
Critical Diagnostic Pitfalls
Stroke can present as isolated altered mental status without classic focal deficits - 70% of missed ischemic stroke diagnoses presented with altered mental status rather than obvious focal signs. 1, 3, 2 This makes CT mandatory even when focal deficits are subtle or absent in high-risk patients.
Normal neurological examination does not exclude serious pathology - In mild head injury, 18.4% of patients had intracranial lesions on CT, with 5.5% requiring neurosurgical intervention despite minimal examination findings. 2
Postictal (Todd's) paralysis mimics stroke - Transient hemiparesis can persist hours to days after seizure, but tongue abrasion is pathognomonic for tonic-clonic activity and should prompt observation rather than reflexive stroke treatment. 3 However, CT is still warranted to exclude hemorrhage or mass lesions.
When MRI Supersedes CT as Initial Imaging
Subacute or chronic neurological deficits (>7 days) without acute deterioration favor MRI over CT as the initial study, as MRI is more sensitive for: 1
- Subtle cortical contusions 1
- Traumatic axonal injury 1
- Small ischemic infarcts 1
- Posterior fossa pathology 1
Persistent unexplained deficits after negative CT warrant MRI as second-line imaging, particularly if symptoms persist beyond 24-48 hours. 1, 3, 2
Low-Yield Scenarios (Clinical Judgment Required)
Elderly patients with new-onset delirium lacking high-risk features have very low diagnostic yield on CT, though medicolegal considerations often drive imaging decisions. 2 The ACR emphasizes that determination of imaging need "falls on the evaluating clinician's judgment" when risk factors are absent. 1