Subarachnoid Hemorrhage (SAH) — CT Brain (Non-contrast)

Core radiological features (concise):

1) Hyperdensity in subarachnoid spaces

• Acute blood appears hyperdense (bright)
• Typical locations:
  • Basal cisterns (suprasellar, interpeduncular, ambient)
  • Sylvian fissures
  • Interhemispheric fissure
  • Cortical sulci

2) “Star sign” (basal cistern pattern)

• Star-shaped hyperdensity in basal cisterns around Circle of Willis
• Classic for aneurysmal SAH

3) Sulcal effacement with hyperdense sulci

• Blood outlines sulci → prominent hyperdense cortical sulci
• May coexist with early cerebral edema → sulcal effacement

4) Intraventricular extension (common)

• Hyperdensity within ventricles (especially occipital horns)
• May show fluid–fluid levels

5) Hydrocephalus

• Acute obstructive or communicating hydrocephalus
• Findings:
  • Ventricular dilatation
  • Periventricular lucency (transependymal CSF seepage)

6) Loss of gray–white differentiation (severe cases)

• Due to global cerebral edema (esp. massive SAH)

7) Distribution clues to etiology

• Aneurysmal SAH → basal cistern dominant
• Traumatic SAH → cortical sulci over convexities
• Perimesencephalic SAH → localized around midbrain, limited spread

One-line mnemonic

“Bright blood in cisterns, sulci, fissures ± ventricles + hydrocephalus”