Hydranencephaly is the most severe form of destructive brain lesion, probably due to bilateral internal carotid artery occlusion as well as primary vascular malformations, and possibly intrauterine infection. It is characterized by a complete lack of cerebral tissue and there is covering calvarium, skin dura and leptomeninges.

Incidence: Sporadic occurrence with an incidence of 1-2.5 per 10,000 births.

Sonographic findings:

Fig 1, Fig 2

    Hydranencephaly:  Transverse scan of the skull: absent brain tissue, present falx cerebri (arrow), abnormal fused thalamus (*)

    Hydranencephaly:  Transverse scan of the skull: absent cerebral tissue, present falx cerebri (arrow), abnormal fused thalamus, and normal posterior fossa (*)

    Hydranencephaly:  Transthalamic view: totally destructive brain lesion (solid circle) but preserving thalamus (*) and posterior fossa

    • A fluid-filled cranium with a complete lack of cerebral tissue.
    • Presence of falx cerebri.
    • Macrocephaly.
    • Normal midbrain, brain stem, basal ganglia, and posterior fossa.
    • Polyhydramnios in most cases.
    • The main differential diagnosis is severe hydrocephalus, hydrolethalis and alobar holoprosencephaly, especially the pancake type (see holoprosencephaly).
    • Pitfalls:
      • The preserved dura and arachnoid can be confused with very severe hydrocephalus. Color Doppler proves useful for the differentiation. The presence of frontal cerebral cortex is indicative of severe hydrocephalus instead of hydranencephaly.
      • The initial diagnosis may be difficult when the infarction and hemorrhage is an evolving process. Recent hemorrhage is echogenic whereas an organizing clot has a more translucent texture. Layering of the debris may masquerade as cortical tissue.
    • Usually diagnosed between 20 and 30 weeks, although it may be detected as early as 11-13 weeks of gestation.

    Associations: Rare.

    Management: Termination of pregnancy should be offered.

    Prognosis: Uniformly fatal, though a case of survival of 20 years with a minimally conscious state was reported.

    Recurrence risk: Sporadic.