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Key Points

  • Hydranencephaly is a rare condition in which the cerebral hemispheres are virtually absent.

  • The typical case is that of an isolated finding without additional abnormalities.

  • The diagnosis should be expected when a large cystic mass fills the cranial cavity and there is no recognizable cerebral cortex.

  • The antenatal natural history is not well known but appears to represent an evolving intrauterine process secondary to a vascular insult.

  • Correct diagnosis is important for the management of these cases. Vaginal delivery is optimal.

  • The long-term outcomes associated with complete hydranencephaly are extremely poor.

  • In most cases, there is no recurrence risk since hydranencephaly is most often associated with a destructive process rather than with a primary malformation.


Hydranencephaly describes a condition in which the cerebral hemispheres are virtually absent. The hemispheres are replaced by membranous sacs containing cerebrospinal fluid. The meninges and skull are intact. The cerebellum and brainstem are typically normal. The falx is usually present but may be partially or completely absent. Hydranencephaly is considered the most severe form of a spectrum of disorders that includes porencephalic cyst and schizencephaly. It is differentiated from extreme hydrocephalus by the lack of any identifiable cerebral cortex in hydranencephaly.

The most commonly accepted mechanism for the development of hydranencephaly is bilateral internal carotid artery occlusion resulting in cerebral infarction. Myers (1969) described the surgical ligation of the common carotid arteries and jugular veins of a rhesus monkey fetus at 84 to 86 days of gestation. On subsequent postmortem examination the fetal cranium was fully developed; however, the cerebral hemispheres were absent and replaced by thin membranous sacs filled with cerebrospinal fluid, while the brainstem and cerebellum were normal (Myers, 1969). Prenatal infections including toxoplasmosis (Altshuler, 1973; Plantaz et al., 1987), cytomegalovirus (Kubo et al., 1994), rubella (Deshmukh et al., 1993), and herpes simplex infections (Christie et al., 1986; Hutto et al., 1987) have also been associated with hydranencephaly. Hemorrhagic states such as familial factor XIII deficiency have also been reported (Takada et al., 1989).

The typical case of hydranencephaly is that of an isolated finding with no additional abnormalities. A variety of syndromes has been reported in association with hydranencephaly, including trisomy 13 (Dixon, 1988), agnathia malformation complex (Persutte et al., 1990), hypoplastic thumbs (Norman and Donnai, 1992), lethal multiple pterygium syndrome (Mbakop et al., 1986), and both renal aplastic dysplasia and polyvalvular developmental heart defect (Bendon et al., 1987). Four cases of hydranencephaly associated with severely dysplastic kidneys have also been reported (Gschwendtner et al., 1997). Hydranencephaly may occur in a surviving co-twin following single intrauterine fetal demise in a monochorionic pregnancy (Hahn et al., 2003). In addition, although this condition is usually sporadic, affected siblings (...

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