NASAH – Nonaneurysmal Subarachnoid Hemorrhage

Checklist of DDx for NASAH:

  • perimesencephalic NASAH
  • occult aneurysm
  • intracranial or spinal vascular malformations
  • intracranial arterial dissection
  • sickle cell disease – can cause aneurysms, or SAH may result from fragile collateral vessels; recent transfusion and corticosteroid therapy may be risk factors
  • pituitary apoplexy – p/w sudden onset of headache and vomiting; heralded by vision change and accompanied by extraocular nerve palsy; MRI will demonstrate tumor
  • cocaine abuse – associated with both aSAH and NASAH; mechanism of latter unknown bur prob related to acute BP surge or underlying hypertensive or toxic vasculopathy
  • cerebral venous thrombosis – less abrupt than aneurysmal rupture, bleeding is localized and superficial; check for thrombosis on venous phase of DSA or on MRI
  • bleeding disorders / anticoagulant therapy – rare, systemic bleeding usually accompanies SAh if this is the primary cause, otherwise, assume an underlying aneurysm; PNSAH can have more extensive hemorrhage in the setting of reduced antiplatelet activity
  • traumatic SAH – if no clinical history available, radiologic clues [localized bleeding in superficial sulci, adjacent skull fracture, cerebral contusion, external evidence of trauma] is present
  • amyloid angiopathy – in older adults; restricted bleed, often to a single sulcus; microbleeds and/or superficial siderosis on MRI
  • spinal aneurysms – prominent neck or back pain and myeloradicular symptoms
  • brain or cervical tumors
  • Moyamoya disease – usually associated with aneurysms, but SAH can occur rarely due to rupture of fragile transdural anastomotic vessels
  • Other causes: cerebral vasculitis, reversible vasoconstriction syndrome, cerebral hyperperfusion syndrome after carotid endarterectomy, reversible posterior leukoencephalopathy syndrome

Diagnostic work-up:

  • emergent CT head
  • lumbar puncture [if CT head negative and suspicion high]
  • basic labs: CBC, CMP, coagulation studies, tox screen
  • baseline echocardiogram
  • conventional digital subtraction cerebral angiography [DSA] on all patients unless CT/CTA adequately defines the pathogenesis
  • repeat DSA within 4-14 days after an initial negative study  NOTE:  False negative rate of initial DSA in NASAH is ~7.1% [2]
  • MRI with gadolinium contrast of brain and spinal cord if angiography negative
  • some patients will not have an etiologic diagnosis after #6 and #7 – if rebleeding occurs, then option to repeat angio of brain and/or surgical exploration and/or surgical exploration



  1. Initial DSA negative SAH ~15%
  2. Reasons for a negative DSA:
    1. a very small microaneurysm
    2. occult aneurysm concealed by hemorrhage or vasospasm
    3. hemorrhage from a venous system
    4. inadequate technique
  3. perimesencephalic NASAH (PN-SAH) – hemorrhage pattern restricted to perimesencephalic or prepontine cisterns, no aneurysms on DSA, low rates of rebleed and vasospasm, good recovery
    1. center hemorrhage located immediately in front of midbrain or within perimesencephalic, prepontine or medullary cisterns
    2. absence of IPH
    3. extension of blood into Sylvian fissure with no more than a minute amount of blood in the lateral Sylvian fissure
    4. absence of frank IVH
  4. Non-perimesencephalic SAH (NPN-SAH) – does not satisfy criteria above, but negative DSA
  5. As a general rule, in PNSAH, provided that the initial DSA was technically adequate and revealed no vasospasm, a repeat DSA might not be required.  However, in NPN-SAH, repeat DSA is necessary due to the possibility of aneurysmal SAH, even if the initial DSA is negative.
  6. DSA has high sensitivity and specificity for detection of cerebral aneurysms and is associated with some complications (SAH-specific mortality 0.17% of patients, neurological morbidity in 3.2% of patients, permanent disability in 0.04%)


[1] Uptodate. Nonaneurysmal subarachnoid hemorrhage, Farhan Siddiq, MD.  Accessed January 23, 2016.

[2] Yu, Dong-Woo et al. “Subarachnoid Hemorrhage With Negative Baseline Digital Subtraction Angiography: Is Repeat Digital Subtraction Angiography Necessary?”. Journal of Cerebrovascular and Endovascular Neurosurgery 14.3 (2012): 210. Web.

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