Fig. 1 Fistulous pial arteriovenous malformation with a high-flow shunt. Although they typically present in early childhood when they classically lead to psychomotor developmental retardation or cardiac insufficiency, they can also present later in life; this typically happens with signs of venous congestion, i.e., epilepsy, or even a cognitive decline. Multiple shunts of this type are characteristic of HHT (hereditary haemorrhagic telangiectasia)