Hydranencephaly is a rare encephalopathy that occurs in-utero. It is characterised by destruction of the cerebral hemispheres with transformation into a membranous sac containing cerebrospinal fluid and the remnants of cortex and white matter 1.
This is a rare disorder with an incidence of 0.2% in infant autopsies 5.
The condition may be diagnosed prenatally using ultrasound or foetal MRI. However, it may present in neonates with seizures, respiratory failure, flaccidity or decerebrate posturing with a vegetative existence 5.
- consequential arthrogryposis
- renal aplastic dysplasia
- poly-valvular developmental heart defect
- Fowler syndrome
- trisomy 13
There is complete absence of the cerebral hemispheres and often, the falx. They are replaced by a sac-like structure containing CSF surrounding the brainstem and basal ganglia 1.
The outer layer is composed of leptomeninges while the inner layer of cortex and white matter filled with CSF and necrotic material. It may be considered a gross polporencephaly.
Five aetiologies have been described.
- infarction - bilateral occlusion of the supra-clinoid segment of the internal carotid arteries or of the middle cerebral arteries 3
- leukomalacia - an extreme form of leukomalacia formed by confluence of multiple cystic cavities 4
- diffuse hypoxic-ischemic brain necrosis - fetal hypoxia due to maternal exposure to carbon monoxide or butane gas may result in massive tissue necrosis with cavitation and resorption of necrotized tissue 1
- infection - necrotizing vasculitis or local destruction of the brain tissue secondary to intrauterine infection, e.g. congenital toxoplasmosis, cytomegalovirus, and herpes simplex infections (HSV) 1,8
thromboplastic material from a deceased co-twin -
- monochorionic twins have presented with a variety of cerebral lesions.
- lesions in the recipient twin result from emboli or thromboplastic material originating from the macerated co-twin 4
All modalities able to image brain parenchyma can be used to identify the features of this hydranencephaly including ultrasound (ante and post natal), MRI (ante and post natal) and CT. In all cases, the anatomical features are the same, although they are demonstrated to a variable degree according to the abilities of each modality. MRI is, as is usually the case, the gold standard.
Typically there is essentially no remaining cortical tissue, with preserved thalami and posterior fossa. Often islands of residual tissue is seen typically at the occipital poles and orbitofrontal regions. The falx is usually present, and the hemicranium filled with fluid, in which choroid can often be identified.
Antenatal ultrasound, or vascular imaging will demonstrate absence of the middle cerebral arteries.
Treatment and prognosis
Hydranencephaly is not compatible with a prolonged life after birth, with the vast majority of live births dying prior to one year of age. Termination of pregnancy is usually considered justifiable due to this reason.
General imaging differential considerations include:
- severe obstructive hydrocephalus / fetal hydrocephalus 8
- cortex is identifiable albeit thinned
- middle cerebral arteries preserved
alobar holoprosencephaly +/- very large dorsal cyst of holoprosencephaly
- usually coexisting midline facial abnormalities
- no falx
- residual cortical tissue often has a cup or pancake morphology, fused across the mid-line anteriorly
- severe open lip schizencephaly
- focal cortical defect lined by polymicrogyic cortex
- 1. Article from : The fetus.net
- 2. Warkany J: Congenital malformation. Chicago Yearbook Medical Publishers pp 221-237, 1981.
- 3. Myers RE. Brain pathology following fetal vascular occlusion: an experimental study. Invest Ophthalmol. 1969;8 (1): 41-50. Invest Ophthalmol (link) - Pubmed citation
- 4. Larroche JC, Droullé P, Delezoide AL et-al. Brain damage in monozygous twins. Biol. Neonate. 1990;57 (5): 261-78. Pubmed citation
- 5. Dähnert W. Radiology review manual. Lippincott Williams & Wilkins. (2003) ISBN:0781738954. Read it at Google Books - Find it at Amazon
- 6. Callen PW, Hashimoto BE, Newton TH. Sonographic evaluation of cerebral cortical mantle thickness in the fetus and neonate with hydrocephalus. J Ultrasound Med. 1986;5 (5): 251-5. J Ultrasound Med (abstract) - Pubmed citation
- 7. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 8. Ketonen L, Hiwatashi A, Sidhu R. Pediatric brain and spine, an atlas of MRI and spectroscopy. Springer Verlag. (2005) ISBN:3540213406. Read it at Google Books - Find it at Amazon
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