Pathology
They are caused by occlusion of one of the small penetrating end-arteries at the base of the brain, thought to result primarily from in situ microatheroma formation, or lipohyalinosis 2 (c.f. cortical infarcts where embolisation of distal thrombus is the primary aetiology).
Pathologically, they are small holes of encephalomalacia and are traversed by a cob-web-like mesh of fibrous strands.