When should a repeat head computed tomography (CT) scan be performed in patients with head injury and subarachnoid hemorrhage (SAH)?

Repeat Head CT After Head Injury and SAH

In patients with traumatic subarachnoid hemorrhage (SAH), a repeat head CT scan should be performed at 6 and 24 hours after onset to exclude hemorrhage expansion and document final hemorrhage volume, even in neurologically stable patients. 1

Timing of Repeat Head CT in SAH

Evidence-Based Recommendations:

• First 24 hours:
  • Initial repeat CT at approximately 6 hours after onset 1
  • Second repeat CT at approximately 24 hours after onset 1
  • This timing protocol is adequate to exclude hemorrhage expansion (HE) and document final hemorrhage volume in most cases 1

Rationale for Early Repeat Imaging:

• Hemorrhage expansion (HE) occurs early after SAH and is an independent predictor of mortality and poor functional outcome 1
• Prospective data shows substantial HE occurs in:
  • 26% of patients at 1 hour after baseline scan
  • Additional 12% of patients at 20 hours after baseline scan 1
• The frequency of HE decreases over time:
  • 15% between 6-12 hours
  • 6% between 12-24 hours
  • Extremely rare (0%) after 24 hours 1

Special Considerations

Neurological Status:

• Repeat head CT is particularly important when:
  • Neurological status deteriorates 1, 2
  • Patient has impaired level of consciousness limiting clinical examination 1
  • GCS score <15 after 24 hours 1

Intraventricular Hemorrhage (IVH):

• Delayed IVH has been reported in 21% of patients with no initial IVH 1
• Delayed IVH is associated with:
  • Delayed hemorrhage expansion
  • Increased mortality and poor outcomes
  • Potential need for emergency surgical intervention 1

Anticoagulation/Antiplatelet Therapy:

• Patients on anticoagulant or antiplatelet therapy may warrant closer monitoring, though evidence suggests delayed ICH is still rare in these patients 1

Beyond 24 Hours

After the first 24 hours, the need for additional imaging should be guided by the clinical picture of the patient rather than routine protocol 1. Hemorrhage expansion after 24 hours is extremely rare (0%) 1.

Utility of Repeat CT in Mild TBI with SAH

For patients with mild TBI (GCS 13-15) and isolated SAH:

• Recent studies question the need for routine repeat CT in neurologically stable patients with mild TBI 3, 4
• A single-institution study found radiological progression in only 1.89% of patients with isolated SAH in mild TBI, with no neurological deterioration observed 4
• Another study found that less than 10% of patients with mild TBI and isolated SAH had worsening on repeat CT scanning 3

Important Caveats

1. CT-Occult Injuries: Isolated SAH on CT may not be truly isolated. Up to 45.6% of patients with apparent isolated traumatic SAH on CT have additional intracranial injuries detected on MRI, including axonal injury (65.4%), subdural hematoma (42.3%), and intracerebral contusion (23.1%) 5

2. Specific SAH Patterns: Subfrontal/temporal intraparenchymal contusions have a significantly higher rate of progression (53%) compared to other types of intracranial hemorrhage 6

3. Predictors of Progression: Significant predictors of progression on head CT include:

   • Use of anticoagulation
   • Age over 65 years
   • Volume of intracranial hemorrhage >10 ml 6

4. Neurological Examination: Changes in neurological examination are strongly associated with the need for neurosurgical intervention (odds ratio 3.98) 7

Bottom Line

While some recent studies question the need for routine repeat imaging in mild TBI with isolated SAH, the 2022 American Heart Association/American Stroke Association guidelines still recommend follow-up CT scans at approximately 6 and 24 hours after onset in patients with SAH to exclude hemorrhage expansion and document final hemorrhage volume 1. This approach is particularly important given that hemorrhage expansion is an independent predictor of mortality and poor functional outcome.