Vascular malformations

Vascular malformations come in different flavours.

Types:

1. Arteriovenous malformation.
   • Most important clinically - highest risk of bleeding.
2. Varix.
   • One large (dilated) vein.
3. Venous angioma.
   • Many small veins.
4. Caverous malformation.
   • Vessels are back-to-back (no intervening parenchyma).

Also see: Sturge-Weber syndrome.

Arteriovenous malformation

General

• High risk for bleeding vis-a-vis other vascular malformations.

Gross

Features:

• Classically wedge-shaped - with base toward superficial aspect and apex toward deep aspect (like pulmonary infarcts).
• Usually middle cerebral artery distribution.

Microscopic

Features:

• Large vessels with eccentric wall thickening.
  • "Large" = ~ 0.5 mm (0.25-1.0 mm).
    • 0.25 mm = ~ 31 RBC diameters across.

Image: Cerebral AVM (WC).

Notes:

• There is usually one feeding artery.
  • The artery is often not seen.
• Arteries have a well-defined internal elastic lamina and an external elastic lamina (best seen on elastic trichrome).
  • Veins do not have an external elastic lamina and have a poorly developed/thin internal elastic lamina.

Cavernous angioma

General

• Usually diagnosed by radiology.

Microscopic

Features:

• Vessels back-to-back/little intervening parenchyma.
  • Muscle is absent in the vessel walls - key feature.