What is the presumed aetiology?
Five mechanisms have been described with some overlap: infarction; leukomalacia; diffuse hypoxic-ischemic brain necrosis; infection; thromboplastic material from a deceased co-twin.
The posterior fossa structures are inferiorly displaced and the fourth ventricle is not well seen. Higher cuts demonstrate marked cerebral destruction of both cerebral hemispheres predominately in the distribution mid cerebral arteries with minimal residual tissue identified both anteriorly and posteriorly. The anterior fontanelle is bulging.