What is the appearance of a bleed on a non-contrast computed tomography (CT) scan?

Appearance of Bleeding on Non-Contrast CT

Acute bleeding appears as hyperdense (bright/white) areas on non-contrast CT, with attenuation values typically ranging from 50-90 Hounsfield Units (HU), though acute hemorrhage can reach higher values. 1

Acute Hemorrhage Characteristics

Hyperdensity is the hallmark finding:

• Acute blood appears as homogenous hyperdensity that is brighter than surrounding brain tissue 1
• The high attenuation reflects clot formation and increased protein concentration from hemoglobin 2
• Hyperdense basilar artery (when measuring vessel density) has optimal cut-off of 40-42 HU for detecting thrombosis 1
• In cerebral venous thrombosis, acutely thrombosed veins and sinuses appear as homogenous hyperdensity, best visualized when CT slices are perpendicular to the vessel 1

Location-specific patterns:

• Intracerebral hemorrhage appears as focal hyperdense mass within brain parenchyma 1
• Subarachnoid hemorrhage appears as hyperdensity in the subarachnoid spaces 1
• Subdural and epidural hematomas appear as extra-axial hyperdense collections 2
• Retroperitoneal bleeding shows high attenuation in the retroperitoneal space 1

Evolution Over Time

The appearance changes as blood ages:

• Acute phase (hours to days): High attenuation/hyperdensity due to clot formation and retraction 1, 2
• Subacute phase (days to weeks): Mixed attenuation as clot begins to lyse; may become isodense to brain tissue 1
• Chronic phase (weeks to months): Low attenuation/hypodensity as tissue breakdown occurs and hemosiderin deposits form 1, 2

Important Diagnostic Considerations

Sensitivity limitations:

• Non-contrast CT can be normal in early or small hemorrhages 1
• Only 30% of cerebral venous thrombosis cases show abnormalities on initial non-contrast CT 1
• Beam hardening artifact in the posterior fossa can limit detection of posterior circulation hemorrhages 1

Distinguishing features for hemorrhage acuity:

• High and mixed attenuation indicates acute to subacute bleeding and possible rebleeding 1
• Low attenuation suggests subacute to chronic blood products 1
• Sentinel clot sign can suggest bleeding site even without active extravasation 1

Common Pitfalls

False positives and confounders:

• Contrast extravasation after interventional procedures can mimic hemorrhage, appearing hyperdense immediately post-procedure 3, 4
• Metallic hyperdensity (>150 HU) after intra-arterial procedures more reliably indicates true hemorrhage 4
• Cortical hyperdensity patterns may resolve spontaneously without representing true hemorrhage 4
• Calcifications can appear hyperdense and be mistaken for acute blood 2

When to pursue additional imaging:

• If clinical suspicion remains high despite normal non-contrast CT, proceed to CT angiography or MRI 1
• MRI with gradient echo sequences is more sensitive than CT for detecting chronic hemorrhage and microbleeds 5
• CT angiography detects active bleeding at rates as low as 0.3 mL/min 1