CT Detection Timeline for Slow Brain Bleeds
CT should be performed ideally within 1 week of symptom onset to reliably demonstrate acute hemorrhage, though acute blood can be detected immediately on CT scan. 1
Immediate Detection (Hyperacute Phase)
- Acute blood is easily and accurately identified on CT immediately after bleeding begins, as CT is considered the gold standard for detecting acute hemorrhage 1
- The term "slow bleed" is somewhat misleading—even ongoing hemorrhages show up on CT as soon as blood accumulates in sufficient quantity to create density differences 1
Time-Dependent Detection Sensitivity
Within 3 Hours
- Hematoma expansion occurs in 38% of patients scanned within 3 hours of onset, indicating active bleeding is detectable but may progress 1
- 36% of patients scanned within 3 hours show subsequent enlargement on repeat imaging, demonstrating that early scans may capture evolving hemorrhages 2
3-6 Hours Window
- 16% of patients show hematoma expansion when initial CT is performed at 3-6 hours 2
- Active bleeding continues in a substantial minority during this timeframe 2
6-24 Hours Window
- CT performed within 1 week reliably demonstrates high density consistent with recent hemorrhage 1
- Between 6-12 hours: 15% show expansion 2
- Between 12-24 hours: 6% show expansion 2
- After 24 hours, enlargement is extremely rare (0%) 2
Critical Timing Considerations
Optimal Imaging Window
- Brain imaging should be performed as soon as possible after onset of clinical symptoms suspicious of hemorrhage 1
- To confirm recent hemorrhage, the high density on CT should have a Hounsfield value consistent with acute blood 1
Delayed Hemorrhage Risk (Special Populations)
- Anticoagulated patients can develop delayed intracranial hemorrhage up to 48-72 hours after trauma, even with initially negative CT 3
- These patients warrant 24-hour observation and repeat imaging, as delayed hemorrhage risk is 1.4-4.5% 4
- Elderly patients ≥65 years on aspirin showed 4% delayed ICH rate 4
Practical Clinical Algorithm
For Spontaneous Hemorrhage
- Perform initial CT immediately upon presentation 1
- Repeat CT at 6 and 24 hours after onset in neurologically stable patients to exclude hematoma expansion 4
- No routine imaging needed after 24 hours in stable patients, as expansion after this point is extremely rare 2
For Traumatic Brain Injury
- Single negative CT is sufficient for neurologically stable patients without anticoagulation 4
- Anticoagulated patients require 24-hour observation with repeat imaging even if initial CT is negative 4, 3
Key Clinical Pitfall
The critical error is assuming a "slow bleed" won't show on CT—any hemorrhage with sufficient volume to cause symptoms will be visible on CT. The real issue is that bleeding may be ongoing and expand over hours, which is why repeat imaging within 24 hours is recommended for at-risk patients, not because the initial bleed is invisible 1, 2