Introduction
Background
The word hydranencephaly is a fusion of hydrocephalus and anencephaly, but the condition actually represents a distinct disorder. The condition is characterized by near-total or total absence of the cerebral cortex and basal ganglia. The thalami, pons, cerebral peduncles, and cerebellum are usually present, as may be a small amount of tissue from the occipital, frontal, and temporal lobes.1
See also the following related eMedicine articles:
Anencephaly
Hydrocephalus [Neurology]
Hydrocephalus [Neurosurgery]
Pathophysiology
Although hydranencephaly is not a well-defined entity, it is considered to be the result of a destructive process or lesion in a previously normal brain. The changes resulting in hydranencephaly can occur at any time from the 11th or 12th week of gestation through the first postnatal year.
Hydranencephaly usually occurs sporadically, although Witters and colleagues reported that a rare, specific form of the disorder, Fowler-type hydranencephaly, appears to have an autosomal recessive inheritance.2 The most commonly suspected causes of the nongenetic form of hydranencephaly are in utero vascular accidents and infections, such as those caused by Toxoplasma gondii, cytomegalovirus, and herpes simplex, which can cause necrotizing vasculitis and encephalitis.3,4
Placental abnormalities, diffuse hypoxic-ischemic brain necrosis, the toxic effects of drugs, and thromboplastic material embolized from a deceased co-twin also have been implicated as causative factors.5,6,7 Moreover, the incidence of hydranencephaly is increased in the fetuses of mothers who smoke.
Knowledge about possible etiologies of hydranencephaly comes from various observations and experiments.8 Studies in sheep and monkeys have demonstrated that bilateral ligation of the carotid arteries results in destruction of the cerebral hemispheres, with relative preservation of the portions of the brain supplied by the posterior circulation, giving an appearance similar to that of hydranencephaly.9
See also the following related eMedicine topic:
Brain Death in Children
Toxoplasmosis, CNS
Frequency
United States
Hydranencephaly occurs in less than 1 in 10,000 births.
International
Hydranencephaly occurs in less than 1 in 10,000 births.
Mortality/Morbidity
Hydranencephaly is associated with a markedly reduced life expectancy, with the condition often resulting in stillbirth or a lifespan of less than 1 year. However, there are reports of prolonged survival. With aggressive care, patients can live into their third decade.12
- The variability of survival is probably related to the severity of involvement of brain structures as well as to the aggressiveness of nursing care.
- Prolonged survival has not proven to be associated with an improvement in responsiveness or awareness.13
Race
No known race predilection exists.
Sex
No known sex predilection exists.
Age
Hydranencephaly is primarily a disease of the fetus; encephaloclastic encephalomalacia can occur in cases of severe perinatal insult.14
Anatomy
Hydranencephaly is a loss of the cerebral tissues supplied by the anterior circulation (that is, the internal carotid arteries), with preservation of tissue supplied by the posterior circulation (specifically, the vertebrobasilar system). The portions of the brain supplied by the anterior and posterior circulations can be variable. However, the posterior circulation typically supplies the posterior fossa structures, occipital lobes, and thalami, whereas the anterior circulation supplies the temporal, parietal and frontal lobes. The thalami typically receive their blood supply from posterior circulation perforating vessels, which is why the thalami are preserved in cases of hydranencephaly.
The anterior or posterior circulation may supply the basal ganglia, and feeding vessels may originate from both circulations. In addition, portions of the posterior and medial parietal lobes can have a blood supply from the posterior circulation, although they are usually fed by the middle cerebral artery (MCA) and anterior cerebral artery (ACA), which are anterior branches.
Therefore, hydranencephaly is anatomically characterized by a loss of the cerebral mantle, with variable preservation of small remnants of the occipital and temporal lobes, as well as, at all times, small, basilar portions of the frontal lobes. The thalami and posterior fossa are preserved, as is the brainstem (although it is usually atrophic at histologic evaluation).
Presentation
At birth, children with hydranencephaly may appear healthy, but developmental delay becomes apparent within a few weeks. Common manifestations of the condition include irritability, abnormal muscle tone, seizures, and increasing head size (as a result of hydrocephalus). Swallowing difficulties lead to malnutrition, aspiration, and pneumonia.
Transillumination of the skull has been used to document the large fluid collection in these patients, but its importance and use have decreased because of the availability of cross-sectional imaging.
Preferred Examination
In utero, hydranencephaly is frequently diagnosed with ultrasonography. Magnetic resonance imaging (MRI) is probably the best modality for the overall evaluation of the anomaly and for the documentation of cortical remnants.15,16
Limitations of Techniques
Postnatally, cranial ultrasonography can detect the absence of cerebral tissue, differentiated from alobar holoprosencephaly by the cleaved thalami and the presence of the falx cerebri. Because the brain beneath the fontanelle is clearly visible, absence of any cortical remnant at this level is helpful in the important differentiation of hydranencephaly from severe hydrocephalus. However, if the fontanelle is small or if appropriate high-frequency transducers are not available, it is possible in severe hydrocephalus to overlook a thin rim of cortical mantle.
On computed tomography (CT) scans, cortical tissue below the parietal bony convexity may be overlooked. In these cases, thin sections and overlapped coronal reconstructions may be helpful. In severe hydrocephalus, MRI can reliably depict the remaining cerebral cortical rim.15,16
Differential Diagnoses
Other Problems to Be Considered
Anencephaly
Neonatal hydrocephalus
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References
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Witters I, Moerman P, Devriendt K, et al. Two siblings with early onset fetal akinesia deformation sequence and hydranencephaly: further evidence for autosomal recessive inheritance of hydranencephaly, fowler type. Am J Med Genet. Feb 15 2002;108(1):41-4. [Medline].
Kubo S, Kishino T, Satake N. A neonatal case of hydranencephaly caused by atheromatous plaque obstruction of aortic arch: possible association with a congenital cytomegalovirus infection?. J Perinatol. Nov-Dec 1994;14(6):483-6. [Medline].
Golkar M, Azadmanesh K, Khoshkholgh-Sima B, et al. Serodiagnosis of recently acquired Toxoplasma gondii infection in pregnant women using enzyme-linked immunosorbent assays with a recombinant dense granule GRA6 protein. Diagn Microbiol Infect Dis. Jan 30 2008;[Medline].
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Lubinsky MS, Adkins W, Kaveggia EG. Decreased maternal age with hydranencephaly. Am J Med Genet. Mar 31 1997;69(3):232-4. [Medline].
Watts P, Kumar N, Ganesh A, et al. Chorioretinal dysplasia, hydranencephaly, and intracranial calcifications: pseudo-TORCH or a new syndrome?. Eye. Dec 14 2007;[Medline].
Greene MF, Benacerraf B, Crawford JM. Hydranencephaly: US appearance during in utero evolution. Radiology. Sep 1985;156(3):779-80. [Medline]. [Full Text].
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To WW, Tang MH. The association between maternal smoking and fetal hydranencephaly. J Obstet Gynaecol Res. Feb 1999;25(1):39-42. [Medline].
Bae JS, Jang MU, Park SS. Prolonged survival to adulthood of an individual with hydranencephaly. Clin Neurol Neurosurg. Jan 25 2008;[Medline].
Werth R. Residual visual function after loss of both cerebral hemispheres in infancy. Invest Ophthalmol Vis Sci. Jul 2007;48(7):3098-106. [Medline].
Deshmukh CT, Nadkarni UB, Nair K, et al. Hydranencephaly/multicystic encephalomalacia: association with congenital rubella infection. Indian Pediatr. Feb 1993;30(2):253-7. [Medline].
Poe LB, Coleman L. MR of hydranencephaly. AJNR Am J Neuroradiol. Sep-Oct 1989;10(5 Suppl):S61. [Medline].
Poe LB, Coleman LL, Mahmud F. Congenital central nervous system anomalies. Radiographics. Sep 1989;9(5):801-26. [Medline]. [Full Text].
Lin YS, Chang FM, Liu CH. Antenatal detection of hydranencephaly at 12 weeks, menstrual age. J Clin Ultrasound. Jan 1992;20(1):62-4. [Medline].
Wintour EM, Lewitt M, McFarlane A, et al. Experimental hydranencephaly in the ovine fetus. Acta Neuropathol (Berl). 1996;91(5):537-44. [Medline].
Kim MS, Jeanty P, Turner C, et al. Three-dimensional sonographic evaluations of embryonic brain development. J Ultrasound Med. Jan 2008;27(1):119-24. [Medline].
Further Reading
Keywords
hydrocephalus, anencephaly, absent cerebral cortex, absent basal ganglia, Fowler-type hydranencephaly, macrocrania, microcrania, alobar holoprosencephaly
