How well can an intracranial (within the skull) bleed or hematoma be visualized on a computed tomography (CT) head scan with contrast?

Visualization of Intracranial Hemorrhage on CT with Contrast

Non-contrast CT is the gold standard for detecting acute intracranial hemorrhage, while contrast-enhanced CT may actually obscure hemorrhage and is not recommended as the initial imaging study for suspected intracranial bleeding. 1

Imaging Characteristics of Intracranial Hemorrhage

Non-contrast CT

• Considered the gold standard for detecting acute intracranial hemorrhage 1
• Highly sensitive for identifying acute hemorrhage 1
• Acute hemorrhage appears hyperdense (white) on non-contrast CT 2
  • Acute subdural hematomas: 50-100 Hounsfield units, typically seen within 72 hours of injury 2
  • Chronic subdural hematomas: hypodense (dark), similar to CSF density, generally seen >3 weeks after injury 2

Contrast-Enhanced CT

• Not recommended for initial evaluation of suspected intracranial hemorrhage 1
• May actually obscure subtle hemorrhages due to contrast enhancement 1
• The American Heart Association/American Stroke Association guidelines explicitly state that "initial head CT for acute trauma evaluation should be performed without intravenous contrast because the presence of contrast may obscure subtle hemorrhages" 1
• Only indicated in specific scenarios:
  • When underlying metastatic disease is suspected and MRI is not feasible 1
  • When isodense subdural hematoma is suspected, especially in anemic patients 2
  • For evaluating underlying structural lesions after hemorrhage has been identified on non-contrast CT 1

Diagnostic Algorithm for Suspected Intracranial Hemorrhage

1. First imaging study: Non-contrast head CT

   • Rapid acquisition
   • High sensitivity for acute hemorrhage
   • Can identify location, size, and mass effect 1

2. If hemorrhage is identified and underlying vascular abnormality is suspected:

   • CT angiography (CTA) should be performed 1
   • CTA has >90% sensitivity and specificity compared to catheter arteriography for identifying vascular lesions 1
   • The "CTA spot sign" may help predict hematoma expansion 1, 3

3. For follow-up or when non-contrast CT is negative but clinical suspicion remains high:

   • MRI with gradient echo (GRE) or T2* susceptibility-weighted imaging 1
   • More sensitive than CT for detection of prior hemorrhage and small bleeds, particularly in the posterior fossa or brainstem 1

Common Pitfalls and Limitations

• Contrast administration timing: Administering contrast before initial non-contrast CT can obscure hemorrhage and lead to missed diagnosis 1
• Isodense hematomas: Subacute hematomas may become isodense to brain tissue on non-contrast CT (typically 1-3 weeks after bleeding), making them difficult to detect 4
• Small hemorrhages: Tiny bleeds, especially in the posterior fossa, may be missed on non-contrast CT 1
• Anemia effect: In severely anemic patients, acute hemorrhage may appear isodense rather than hyperdense 2
• Tumor-associated hemorrhage: Bleeding tumors account for approximately 4.4% of intracerebral hematomas and may require contrast-enhanced imaging for proper characterization 5

Special Considerations

• For subarachnoid hemorrhage, non-contrast CT has a sensitivity of approximately 93% overall, decreasing with time from symptom onset 6
• In patients with suspected tumor-related hemorrhage, contrast-enhanced CT or MRI should be performed after initial non-contrast CT 5
• When cerebral venous thrombosis is suspected as a cause of hemorrhage, CT venography (CTV) or MR venography (MRV) is indicated 1

In conclusion, while contrast-enhanced CT has important applications in neuroimaging, it is not the appropriate initial study for detecting intracranial hemorrhage and may actually reduce diagnostic accuracy for this specific purpose.