= liquefaction necrosis of cerebral hemispheres replaced by a thin membranous sac of leptomeninges in outer layer and remnants of cortex and white matter in inner layer, filled with CSF + necrotic debris

Incidence: 0.2% of infant autopsies

Etiology: absence of supraclinoid ICA system (? vascular occlusion / infection with toxoplasmosis or CMV) with intact posterior circulation

= extreme form of porencephaly

• seizures; respiratory failure; generalized flaccidity
• decerebrate state with vegetative existence
• normal skull size / macrocrania / microcrania
• complete filling of hemicranium with membranous sac
• absence of cortical mantle (inferomedial aspect of temporal lobe, inferior aspect of frontal lobe, occipital lobe may be identified in some patients)
• brainstem usually atrophic
• cerebellum almost always intact
• thalamic, hypothalamic, mesencephalic structures usually preserved projecting into cystic cavity
• central brain tissue can be asymmetric
• choroid plexus present
• falx cerebri + tentorium cerebelli usually intact, may be deviated in asymmetric involvement, may be incomplete / absent

Prognosis:NOT compatible with prolonged extrauterine life (NO intellectual improvement from shunting!)

DDx:

1. Severe hydrocephalus (some identifiable cortex present)
2. Alobar holoprosencephaly (facial midline anomalies)
3. Schizencephaly (some spared cortical mantle)