Subarachnoid hemorrhage (SAH)



  • MC traumatic hemorrhage (SAH > SDH)
  • Site of bleeding: Subarachnoid space (between arachnoid & pia)

  • MC cause of spontaneous (non-traumatic) SAH: Rupture of Berry’s aneurysm
  • The defect in berry aneurysm is: Degeneration of tunica media (Muscle layer).


  • MC site of Berry’s aneurysm: Between Anterior cerebral artery & Anterior communicating artery (absent internal elastic lamina and muscle)
  • LC site of Berry’s aneurysm/ Aneurysm most likely to rupture: Bifurcation of basilar artery (into Posterior cerebral artery)/ Vertebrobasilar junction
  • MC-ly involved cranial nerve in Berry’s aneurysm: CN-III

  • Special note: MCA does not take part in formation of Circle of Willis.

Clinical feature:

  • “Thunder clap headache”/ “Worst headache of life”
  • Neck rigidity.


  • IOC/ Screening investigation of acute SAH: NCCT

  • IOC for cerebral aneurysm in a patient with SAH: CT angiography

  • Best investigation for cerebral aneurysm: DSA (Digital subtraction angiography), as it gives bone free image
  • Lumbar puncture:
    Xanthochromia (Xanthos – Yellow; Chroma – Color) in CSF is highly suggestive of subarachnoid hemorrhage. The colour is due to the hemoglobin degradation products.


  • MC cause of death in SAH due to Berry aneurysm is: Vasospasm → Cerebral ischemia
  • Cerebral salt wasting syndrome (CSW): Hypovolemic hyponatremia caused by release of BNP (causing natriuresis) from brain in response to increased ICT.

Differentiating CSW from SIADH:

  • In both cases, hyponatremia and high urine osmolarity are present
  • But in CSW, clear evidence of volume depletion (i.e. hypotension, decreased skin turgor, elevated hematocrit) is evident
  • By comparison, extracellular fluid volume is normal or slightly increased with SIADH.


  • Medical management by Nimodipine (intracerebrally acting CCB) given for 21 days
  • Intervention to prevent rebleed: Endovascular coiling
  • Intervention in wide mouth aneurysm: Craniotomy + Clipping
  • Coiling is preferred over clipping
  • Platinum based coil is used.

Related topic: Normal MR angio landmarks of neck:

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