Neurosurgery notes/Vascular/Haemorrhagic diseases/SAH/Aneurysm type

Aneurysm type

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SAH

Saccular (berry)

  • A rounded aneurysm with a neck
  • Large vs small vessels
    • Major (named) arteries: occurs at apex of branch points --> site of maximal haemodynamic stress
    • Peripheral arteries: mycotic/trauma
  • Location
    • Carotid system: 90%
        • ACOM: 30%
        • Presentation
          • DI
          • Other hypothalamic dysf(x)
          • Frontal lobe ischaemia abulia and apathy
        • CT
          • SAH in anterior interhemispheric fissure
          • Associated with
            • ICH 60%
            • IVH 80%
            • Hydrocephalus: 25%
            • Infarct: 20%
        • Angiography
          • Compress ipsilateral side to see whether there is collateral filling
          • Determined if either ACA fills from ipsilateral carotid injection if so can be treated with trapping
          • Towne view to better visualize aneurysm as ap and lateral view not able to give 3D DSA view of the anuerysm
            • 25° away from injection side, centre beam 3-4 cm above lateral aspect of ipsilateral orbital rim,
              • Image result for Towne’s view.
        • Approaches
          • Pterional (most common approach)
            • Rt sided normally
            • Lt side used for the follow circumstances
              • Large ACOM pointing Rt: Going from left allows neck to be approached first than dome
              • Dominant Lt A1 feeder: Lt side allows proximal control
              • Multiple Lt side aneurysm
          • Sub frontal
            • For aneurysm pointing superiorly
          • Anterior interhemispheric approach
            • Not used in aneurysm that point superiorly
              • As interhemispheric approach will allow you to meet the dome first therefore you wont have proximal control
            • Has minimal brain retraction
          • Transcallosal
        PCOM: 25%
        • Can occur at two different j(x)
          • PCOM Jx carotid (more common)
          • PCOM Jx PCA
        • 3rd nerve palsy
        • Is still considered a anterior circulation because it occurs between ICA and PCOM
          • ISUIA paper classified these aneurysms as posterior circulation which they quite clearly are not.
        • Angiography:
          • Two pathologies seen with PCOM
            • Infundibulum PCOM: a wide diameter PCOM that narrows down to the normal diameter: its not a pathological PCOM
            • Fetal circulation:
              • Normally the PCA developes from the PCOM and then swap the PCOM for the basilar artery as it’s main supply
              • In fetal circulation this swapping do not occur: PCA supplied by PCOM.
                • If it is fetal circulation when clipping cannot sacrifice PCOM
                • Need to figure out whether there is a fetal circulation by determining whether aneurysm fills with VA injection
        MCA: 20%
        • More specifically between M1 and M2 J(x) aka trifurcation region (although not a true trifurcation region)
        • Approaches
          • Trans-Sylvia approach through a pterional craniotomy: most common
          • Superior temporal gyrus approach
            • Advantage
              • Minimize brain retraction
              • Possible reduced vasospasm from reduce manipulation of proximal vessels
            • Disadvantage
              • Proximal control difficult
              • Slightly larger bone flap
              • Possible inc. risk of seizure
        Others:
        • Carotid terminus bifurcation aneurysm (bifurcation of MCA and ACA) 5%
        • Distal anterior cerebral artery aneurysm (DACA)
          • Distal to ACOM usually at
            • Frontopolar artery
            • Bifurcation of pericallosal and callosomarginal arteries at genus of corpus callosum
          • Tends to be more
            • Postraumatic
            • Mycotic
          • Tend to form more: because the SAH is less here
            • ICH
            • Interhemispheric subdural haematoma
          • Fqly multiple aneurysm
          • Poor results with conservative tx. However, it also ruptures easily because it is fragile and adhere to brain
            • <1cm from ACOM : Pterional craniotomy with partial gyrus rectus resection
            • >1cm distal to ACOM: interhemispheric approach
        • Supraclinoid aneurysm (see anatomy) made of 3 segments
          • Ophthalmic segments
            • Ophthalmic artery aneurysm
              • Presentation
                • 45% SAH
                • 45% visual field defects
                  • Ipsilateral monocular superior nasal quadrantanopsia
                    • Aneurysm compress on lateral portion of optic nerve —> inferior temporal fibre compression
                  • Monocular inferior nasal quadrantanopsia
                    • If the above condition persist and further enlargement of aneurysm form —> upward displacement of nerve against falciform ligament —> superior temporal fibre compression —> both inferior and superior nasal quadrantanopsia forms —> monocular heminanopia
                  • Contralateral superior temporal quadrant defect (junction alone scoot a aka pie in the sky defect)
                    • Aneurysm causing compression at chiasm —> injury of anterior knee of wilbrand (nasal retinal fibres that course anteriorly for a short distance after they decussate in the contralateral optic nerve9i)
                • 10% as both
            • Superior hypophyseal artery aneurysm
              • Has two variant
                • Paraclinoid variant: does not produce visual symptoms
                • Suprasellar variant: when giant acts like a pituitary tumour on CT
          • Communicating segment
          • Choroidal segment
    • Posterior circulation: 10%
      • Basilar: 10%
        • Basilar tip > BA-SCA, BA-VA, AICA
      • Vertebral artery: 5%
        • VA-PICA
    • Multiple: 25% of patients with aneurysm have multiples aneurysm

Fusiform aneurysm: vertebrobasilar system

  • A dilatation of the arterial wall which involves at least 270° of the vessel wall.
  • Fusiform aneurysms are more commonly seen in the posterior circulation,
  • Number
    • > 60 years
    • Male predominance.
  • The pathophysiology is unknown,
    • Some may be related to prior dissections
    • It is therefore possible that the umbrella term of ‘fusiform’ aneurysms includes dilatations of the vessel wall of different aetiology.
  • Dolicoectactic aneurysm
    • A type of fusiform aneurysm
    • Characterized by the uniform pathological dilatation of an entire vessel segment often in association with tortuosity of the vessel itself
  • Classification
    • Incidental
      • Have often a fairly benign natural history
    • But they can also present with ischaemic symptoms, symptoms related to mass effect, and haemorrhage.

Traumatic aneurysm

  • Numbers
    • < 1% of all intracranial aneurysms
    • True incidence is unknown
      • Many may go undetected.
    • 2nd most common type of aneurysm encountered in children and adolescents
      • 5– 15% of all aneurysms in children
    • More prevalent in men
  • Most are pseudoaneurysm
  • Location
    • All major intracranial arteries can be involved
    • Depends on where the injury is
    • ICA (46%)
    • MCA (25%)
    • (ACA) (22%)
  • Subdivided into
    • ‘true’ TAs
      • Composed of all of the three layers of the vessel wall.
      • Due to
        • Direct blunt trauma OR
        • Indirect forces
      • Represent a ‘bulge’ in the vessel.
    • ‘False’ TAs
      • Due to
        • Direct interruption of the continuity of a vessel --> formation of a perivascular haematoma.
      • Composed only of fibrin tissue surrounding a partially organized haematoma.
  • Aetiology
    • Penetrating trauma
    • Blunt trauma: closed head injury
      • Peripheral
        • Impact on falcine edge: Distal anterior cerebral artery
        • Impact on the skull: distal cortical artery aneurysm
          • Associated with
            • Skull fracture
            • Growing skull fracture (post-traumatic leptomeningeal cyst)
              • In paeds: Mean age of injury <1 yr
              • 90% before 3 yrs
              • Skull fracture + dural tear (unsure mech) —> arachnoid invaginate into fracture + pulsation of CSF —> ball valve mech —> enlarging cyst that separates skull fracture
      • Skull base
        • ICA Petrous portion: ass. W/ skull base #
        • Cavernous portion: ass. W/ skull base #
          • Enlargement causes Cavernous sinus syndrome
          • Rupture causes CCF
        • Clinoid portion
      • Iatrogenic pseudoaneurysms
        • After
          • trans- sphenoidal surgery,
          • Craniotomy for tumours and vascular lesions,
          • ETV
          • EVD
  • Natural history of untreated TAs
    • Not well understood.
    • Risk of rupture can be high if progressive enlargement on serial imaging studies.
    • A low index of suspicion is important for adequate diagnosis and in high- risk cases, repeating another vascular imaging study after a negative first one may be indicated,
      • Since TAs may become visible a few days after the trauma.
  • Presentation
    • Delayed intracranial haemorrhage
    • Recurrent epistaxis
    • Progressive CN palsy
    • Enlarging skull fracture
    • Severe h/a
  • Treatment:
    • ICA at skull base: endovascular trapping/embolization
    • Peripheral: clipped or coiled

Dissecting aneurysms

      Fig. 47.3 Left vertebral artery angiography shows a dissecting aneurysm involving the proximal left posterior cerebral artery.
      Left vertebral artery angiography shows a dissecting aneurysm involving the proximal left posterior cerebral artery.
  • A potential, albeit less common, source of SAH.
  • They originate from a dissection: tear through the intima and internal elastic lamina in which blood accumulates between the different layers of the vessel wall.
  • Difference
        • Pseudoaneurysm
        Dissecting aneurysm
        Lack 3 layers of vessel wall
        Has basic components of vessel wall
  • Location
    • Extracranial vertebral
    • Carotid artery
    • Intracranial arteries.
      • Less common
      • V4 segment of the Vertebral artery
      • Location in the anterior circulation is more typical in children and young adults.
  • Clinical features
    • Extracranial dissection which do not cause haemorrhage and generally asymptomatic
    • Intracranial dissecting aneurysms
      • Asymptomatic OR
      • Ischaemic symptoms, headache, or frank haemorrhage

Mycotic aneurysm

  • Aetiology
    • From vascular source (IE)
      • Aneurysm
      • Eg
        • Infective endocarditis.
    • From external source
      • Aneurysm if more proximal
      • Eg
        • Meningitis
        • Severe sphenoidal sinus infections with osteomyelitis and cavernous sinus thrombophlebitis.
  • Numbers:
    • 4% of total intracranial aneurysm
    • 10% of patients with subacute bacterial endocarditis
    • 80% of patients with mycotic aneurysm will have bacterial endocarditis
    • 80% in distal MCA branch
    • 20% of mycotic aneurysm will be multiple
      • Due to multiple emboli
      • Esp in immunodeficient patients and those (partially) treated with inappropriate antibiotics or cytotoxic drugs.
  • Pathophysiology
    • Emboli get push into areas of high blood flow and places where it is easy to seed i.e. branch points
    • Mycotic aneurysms typically involve distal branches and can occur away from branch points.
    • Infectious inflammation starts from the Adventitia and spread inwards
    • Distal arteries do not have vasa vasorum
  • Presentation
    • SAH
    • ICH
  • Investigation
    • Blood and CSF cultures will show the suspected causative agent in two thirds of patients,
      • Last 1/3 will never have a + study
      • Microorganism
            • Streptococcus (S viridian)
            44%
            Staphylococcus (S aureus)
            18%
            Miscellaneous (pseudomonas, enterococcus, corynebacterium)
            6%
    • Radiology
          • A close-up of hair AI-generated content may be incorrect.
  • Treatment:
    • Abx
      • Targeting the offending agent is the main treatment of mycotic aneurysms
      • Abx do not prevent resolution of aneurysm but it reduces infection —> dec. inflammation —> allow fibrosis of aneurysmal wall —> stronger aneurysmal wall —> reduce risk of rupture
      • In some clinical situations, antibiotics can be initiated empirically based on the original infection and standard guidelines.
      • Monitoring of systemic infection should be made through serial blood cultures.
      • Therapy must be continued for 4– 6 weeks or until cultures become negative.
    • Endovascular or surgical treatment can be considered in specific situations (Kannoth and Thomas, 2009).
      • When it is infected, the aneurysm is stuck onto surrounding tissue hard to dissect and friable —> hard to tx surgically
      • Indications for delayed clipping
        • Patients with SAH
        • Inc. size of aneurysm while on abx
        • Failure of size to dec. after 6 wks of abx
      • Early endovascular management
        • Indicated for ruptured infectious arterial aneurysms responding poorly or not at all to treatment.
        • May require sacrifice of the involved arterial segment, even in eloquent areas, after assessing the leptomeningeal anastomotic circulation, because preservation of the artery is usually not possible.
  • Outcome
    • Mortality
      • 80% for ruptured aneurysms
      • 30% for unruptured aneurysms
    • New infectious aneurysms will appear in more than 10% of patients,
      • Important for repeated cerebral angiography at short intervals.

Blister- like aneurysms

  • General
    • Over time, the term blister- like aneurysms has been misused to indicate very small saccular aneurysms at branching sites of the circle of Willis.
    • Definition: small dilatations, hemispherical- shaped and bulging, from non- branching sites of the dorsal wall of the supraclinoid ICA opposite to the origin of the PCom and the anterior choroidal arteries
  • It is controversial whether all blister- like aneurysms represent focal dissections of the ICA or whether there are two distinct types:
    • True blisters which represent a hole in the wall of the vessel
    • Dissecting pseudoaneurysms of the ICA.
  • Numbers
    • 1% of all ruptured aneurysms
  • Characterized by a very fragile wall which makes treatment challenging.
  • Typically diagnosed after a bleed,
  • Difficult to identify on the first catheter angiogram and become more evident only at follow- up.
      vu Fig. 47.4 This 30-year-old woman presented with diffuse SAH. Catheter angiography shows a blister-like aneurysm (a) involving the supraclinoid portion of the right ICA (arrow). (B) The blister-like aneurysm was treated with a flow diverter (arrow).
      This 30-year-old woman presented with diffuse SAH. Catheter angiography shows a blister-like aneurysm (a) involving the supraclinoid portion of the right ICA (arrow). (B) The blister-like aneurysm was treated with a flow diverter (arrow).