Neurosurgery notes/Vascular/AV shunt/Arteriovenous malformations (AVM)/Surgical techniques in AVM surgery

Surgical techniques in AVM surgery

  • Aim:
    • Eliminate all arteriovenous shunting while minimizing the damage to normal functional brain
      • Avoiding the rupture from the abnormal vasculature during this process
  • Surgical techniques
      • Artery first, veins last
      • Controlling superficial feeding arteries early
        • Might use temporary clips until definitive division site is established
      • Controlling deep feeding arteries early
        • by a sulcal dissection and corticotomy
        • Deep arteries
          • lenticulostriate arteries
          • choroidal arteries
          • Superficial arteries that dive into the depths of the sulci before entering the AVM at a deep location.
      • controlling transdural arterial supply
        • Not always present
        • Incising the dura at a distance from the AVM, completing an island of dura on the AVM, to prevent tension placed upon these arteries
          • Like performing convexity meningioma excision
          • If falx is involved, approach from the opposite side of the involved dura
      • Controlling transosseous arterial supply
        • A polo mint craniotomy can be performed
        • This allows bleeding to be controlled at each surface of the craniotomy.
      • Small arterialized vessels connected to the AVM within the white matter are normally veins;
        • Differentiating white matter vessels: veins vs arteries
          • perivascular space is only large around small arteries (and not veins) the absence of CSF surrounding
        • The vast majority of these vessels do not require ligation but should be swept back onto the margin of the AVM with bipolar and sucker.
        • The cumulative effect of dividing small arterialized veins can compromise venous drainage in the AVM
      • Last major vein should be divided after the mass of the AVM is delivered on its venous umbilicus to ensure that all feeding arteries have been divided
      Minimize collateral brain damage with:
      • BP control: via MAP and pulsatile pressure
        • To
          • encouraging brain relaxation
          • protection from ischaemia;
      • Positioning to
        • Prevent venous outflow obs(x) —> optimize brain relaxation
        • Reduce retraction
      • Craniotomy
        • correctly positioned and sized for the AVM and proximal artery exposure (including access across the midline)
      • Retraction minimized on the brain
        • can lead to stroke due to
          • shunt induced ischaemia AND
          • GA induced low BP
        • Can retract the AVM if there is no associated venous outflow compromise);
      Careful ligation of vessel
      • Arterialized veins and remodelled arteries more difficult than normal due to
        • Thinner walls for arterial
        • Thicker walls for veins
      • Technique
        • Small vessel division within the sulci achieved with fine bipolar or microclips;
          • Bipolar
            • With absolutely clean mirror surfaced points and on low setting (to ensure that the vessel wall does not explode before thrombosis has arrested flow within the vessel).
            • Length of diathermy occlusion needs to be longer than would normally be considered when dealing with other pathologies.
          • Microclips
            • are a useful adjunct to bipolars, capable of arresting flow in very thin- walled vessels, diathermy of which might lead to bleeding rather than thrombosis (see earlier)
            • Pros
              • Cause reduce damage to endothelium than bipolar
        • Small vessel division within the corticotomy achieved with a broader, insulated bipolar utilizing adjacent tissue to assist the reinforcement of the wall to be included in the diathermy target.
      Suction (use 2)
      • Fine sucker (e.g. #3 or 4) at the lowest suction necessary to clear CSF and blood.
        • Reduces the accidental disruption of fine thin- walled vessels during the resection.
      • Larger suckers
        • Should be immediately available if problematic bleeding occurs.
      Haemostasis
      • AVM bed should be completely free of bleeding
      • Because of the thin-walled arteries of AVM, there will be minimal vasoconstriction
        • Other pathologies (tumour/cavernoma) have greater amounts of vasoconstriction
        • No bleeding point should be covered by material.
      • If the bleeding point cannot be easily arrested with bipolar or microclip, the source of the bleeding needs to be followed into the brain to achieve a point where the vessel can be secured.
        • This may be facilitated by utilizing two fine suckers by the surgeon, one for sucking the bleeding point and the second for dissecting around this point.