Neurosurgery notes/Vascular/Haemorrhagic diseases/SAH/SAH of unknown aetiology

SAH of unknown aetiology

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SAH

SAH of unknown aetiology (angiogram negative SAH)

Numbers:
  • 10% of SAH
Causes
  • Aneurysm present but not seen in the 1st angiography
    • Incomplete angio:
      • Not seeing PICA
      • No cross fill through the ACOM
    • Degradation of images due to
      • Poor patient cooperation
      • Poor quality equipment
      • Obliteration of aneurysm by the haemorrhage
      • Thrombosis of aneurysm after SAH
      • Microaneurysm: too small to be seen
      • Lack of filling of aneurysm due to vasospasm
    • Nonaneurysmal SAH from source that don’t show on angiography
      • Vascular malformation that are occult to DSA
      • Pretruncal non-aneurysmal SAH
Risk of rebleeding
  • 0.5%/yr
General measures
  • Are still at risk of complication of aneurysmal SAH (although risk might be lower): Vasospasm/hydrocephalus/hyponatremia/rebleeding
  • Repeat angiography
    • 10% positive rate second scan when 1st is negative
      • Repeat angio after 13 days to allow resolution of vasospasm and clot
        • Keep patients in to manage complication of aneurysmal SAH
        • Vasospams highest between day 3 -12, any surgery will exacerbate vasospams hence if you repeat angio at day 13 and then do surgery at day 14.
      • Pay particular attention to area of scan where the CT shows high blood load
    • Do not repeat angio for classical pretruncal SAH or if no blood on CT
  • Other studies
    • MRA
    • CTA
    • Spinal MRI: r/o spinal AVM a rare cause of intracerebral SAH
      • Spinal DSA risky and difficult so not used as first line
  • Surgical exploration
    • For classical blood distribution and load but negative DSA

Nonaneurysmal SAH

Blood distribution
  • Localized to perimesencephalic pattern:
    • Blood is confined mainly in the basal cisterns surrounding the midbrain and constrained by Liliequist’s membrane, but can include the proximal part of the Sylvian fissure.
  • Diffuse pattern
    • Where blood extends into the distal Sylvian or interhemispheric fissures.
Aka
  • Pretruncal nonaneurysmal SAH
  • Perimesencephalic nonaneurysmal SAH
General
  • Pretruncal: in front of the brain stem (truncus cerebri) and not around the mid brain (mesencephalon)
  • SAH extends into interpeduuncular and/or perimedullary cisterns
Number
  • 60% of angiogram neg SAH
  • 50 yrs Mean age
  • 60% male
  • 10% HTN pts
Aetiology of Nontraumatic, nonaneurysmal perimesencephalic hemorrhage (PMH),
  • Venous origin: 96%
  • Rupture of vertebrobasilar aneurysm: 4%
Anatomy
  • Post fossa cistern: perimesencephalic cisterns made up of
      1. Interpeduncular C.
      1. Crural C.
      1. Ambient C.
      1. Quadrigeminal C.
      Perimesencephalic cistern 1. Interpeduncular C. 2. Crural C. Ambient C. 3. Quadrigeminal C. 4. 1
  • Pre-pontine cistern lies immediately anterior to pons
  • Liliequist membrane
        • 3 . CA SCA Bas A Sphen.s,ntß Arach. Memb.
        THREE SEGMENTS OF THE LILIEQUIST MEMBRANE It is formed by either a single or double arachnoid layer and divided into three segments. Sellar, Diencephalic and Nlesencephalic segments
        Three segments of the Liliequist Membrane. It is formed by either a single or double arachnoid layer and divided into three segments. Sellar, Diencephalic and Mesencephalic segments.
    • Remnant of primitive tentorium
    • Forming of a competent barrier in only 20%
    • Form by 3 leaflets
      • Inferior leaflet (M):
        • Mesencephalic membrane
        • Separates interpeduncular cistern from prepontine cistern
      • Posterior leaflet (D):
        • Diencephalic membrane
        • Thicker and more competent
        • Isolates chiasmatic cistern
      • Anterior leaflet (S):
        • Sellar membrane
    • Separates the interpeduncular cistern from
      • Chiasmatic cistern medially
      • Carotid cistern laterally
    • There is a communication between carotid cistern <—> crural cistern <—> interpeduncular cistern
    • Bld in carotid or prepontine cistern: low pressure pretruncal source of bleed
    • Bld in chiasmatic cistern: high pressure aneurysmal bleed
Complication (Walcott et al., 2015).
  • While non-aneurysmal haemorrhage has typically been associated with a benign course,
  • Hydrocephalus
  • Rebleed very low (most studies have zero patients with rebleeds)
  • Spasm: low and might be due to angiographic(iatrogenic) vasospasm
  • Hyponatremia
  • Cardiac abnormalities
  • Unsure cause most likely rupture of a small perimesencephalic vein or capillary
Presentation
  • Severe sudden HA
  • Do not have Tearson or Sentinel h/a
  • Meningismus
  • Photophobia
  • Nausea
  • Rare for LOC and most pt are not critically ill (grade 1/2)
Investigate
  • Bloody LP
  • Negative CTA/DSA
Pretruncal nonaneurysmal SAH diagnostic criteria
  • CT/MRI criteria SCAN MUST BE DONE <2 days from ictus (too long then the aneurysmal SAH will washout)
    • Epicentre of haemorrhage immediately anterior to brain stem: in prepontine or interpeduncular cistern
    • There may be extension into anterior part of ambient cistern or basal part of the Sylvia’s fissure
    • Absence of complete filling of anterior interhemispheric fissure
    • No more than minute amounts of blood in lateral portion of Sylvia’s fissure
    • Absence of frank intraventricular haemorrhage
      • Acceptable to have small amounts of blood in occipital horns of lateral ventricles
  • Other criteria’s
    • Negative high quality 4 vessel angiography
      • Vasospasm does not exclude PTNSAH
    • Appropriate clinical picture
      • No LOC
      • No sentinel H/A
      • SAH grade 1/2
  • If meet criteria for PTNSAH no need for repeat DSA
    • DSA has 0.5% risk of permanent neurological deficit in patients with PTNSAH
Treatment
  • Analgesia
  • Cardiac monitoring
  • Electrolyte monitoring
  • Check fo hydrocephalus
    • Transient ventricular enlargement is common
    • Rare needing shunting
  • NO NEED
    • Hyperdynamic therapy
    • Nimodipine
      • As low incidence of spasm; but no studies done to validate this
    • Activity restrictions
    • Anticonvulsant
    • Reduction of BP
    • Surgical exploration
Nguyen et al 2022- https://doi.org/10.3174/ajnr.A7483
  • 20.8% patients with spontaneous SAH had negative initial DSA findings
  • The SAH CT pattern was
    • Nonperimesencephalic (41%)
    • Perimesencephalic (36%)
    • Sulcal (18%)
    • CT-negative (5%)
  • Repeat DSA in 7.4%:
    • 4 saccular aneurysms
    • 4 atypical aneurysms
    • 2 arteriovenous shunts
  • The overall yield of repeat DSA was
    • 11.3% with nonperimesencephalic
    • 2.2% for perimesencephalic patterns
  • The yield of the second and third DSAs with a nonperimesencephalic pattern was 7.7% and 12%, respectively.
  • Physiologically occult lesions accounted for 6/242 (2.5%) and operator-dependent errors accounted for 7/242 (2.9%) of all angiographically occult lesions on the first DSA.