What does a description of increased intracranial pressure on a computed tomography (CT) scan indicate?

CT Findings of Increased Intracranial Pressure

CT scan findings suggesting increased intracranial pressure include compression or obliteration of basal cisterns, sulcal effacement, ventricular compression (particularly the third ventricle), midline shift >5mm, and signs of herniation—however, CT imaging is unreliable for ruling out elevated ICP and should not replace clinical assessment or direct pressure monitoring when indicated. 1

Key CT Imaging Features

The most reliable CT indicators of elevated ICP include:

• Basal cistern compression or obliteration is the single best radiographic sign, associated with ICP >30 mmHg in over 70% of cases 1, 2
• Sulcal obliteration correlates significantly with measured ICP ≥20 mmHg 2
• Third ventricular compression shows significant association with elevated ICP measurements 2
• Midline shift >5mm suggests increased pressure, though interestingly this finding does not always correlate with actual ICP values 1, 3
• Lateral ventricle compression indicates mass effect and potential pressure elevation 2
• Traumatic subarachnoid hemorrhage is associated with risk of intracranial hypertension 1, 3

Critical Limitations of CT Imaging

A normal or near-normal CT scan does NOT exclude dangerously elevated intracranial pressure. This is a crucial clinical pitfall:

• In adults with suspected encephalitis, less than 5% show imaging changes suggestive of raised ICP, yet many still have elevated pressures 1
• In non-traumatic coma, 3 of 7 patients (43%) with completely normal CT scans had ICP ≥20 mmHg within the first 12 hours 4
• In pneumococcal meningitis, CT imaging can grossly underestimate true ICP values—even failing to detect cerebral herniation when ICP measurements showed values of 44-90 mmHg 5
• In fulminant hepatic failure, CT has little value in detecting cerebral edema despite elevated ICP 6

Clinical Decision-Making Algorithm

When to obtain CT before lumbar puncture (these are contraindications to immediate LP):

• Glasgow Coma Scale <13 or decline in GCS >2 points 1
• New onset seizures 1
• Focal neurological signs (excluding isolated cranial neuropathies) 1
• Papilledema—the only direct clinical indicator of raised ICP 1
• Abnormal posturing 1
• Relative bradycardia with hypertension 1
• Signs suggesting space-occupying lesion 1

After obtaining CT imaging:

• If CT shows significant brain shift, tight basal cisterns, or mass effect causing raised ICP, LP should be reconsidered on a case-by-case basis 1
• If CT is normal but clinical signs of elevated ICP persist, do not assume ICP is normal—consider direct ICP monitoring in appropriate settings 5, 4, 6
• In traumatic brain injury with abnormal CT, >50% of patients will have intracranial hypertension requiring monitoring 1

Specific Populations

In children with papilledema or suspected raised ICP:

• MRI head and orbits is superior to CT for initial evaluation, providing better soft tissue resolution 1
• CT head without contrast may serve as an alternative to detect space-occupying lesions or hydrocephalus 1
• Specific MRI findings for idiopathic intracranial hypertension include posterior globe flattening (56% sensitivity, 100% specificity), optic nerve protrusion (40% sensitivity, 100% specificity), and optic nerve tortuosity (68% sensitivity, 83% specificity) 1

In traumatic brain injury:

• Presence of all five CT signs of elevated ICP (sulcal obliteration, lateral ventricle compression, third ventricle compression, midline shift, herniation) predicts poor functional outcome (OR 4.44) 2
• Hemorrhage location matters: posterior fossa (OR 3.208) and basal ganglia (OR 3.079) hemorrhages are associated with increased mortality 2
• Hemorrhage volume >30cc significantly increases death risk (OR 3.702) 2

Common Pitfalls to Avoid

• Never rely solely on CT to exclude elevated ICP in comatose patients—clinical assessment and direct monitoring are essential when suspicion is high 1, 5, 4
• Do not delay treatment waiting for CT if clinical signs clearly indicate herniation 1
• In focal lesions (basal ganglia or hemispheric), local CSF space obliteration does not reliably predict generalized raised ICP 4
• CT is a tool for detecting structural causes and supporting clinical assessment, not a definitive measure of intracranial pressure 1, 5