hydranencephaly

hydranencephaly the transducer is moved anteriorly and posteriorly in a coronal plane to demonstrate the virtually empty cranial cavity. note the presence of the falx cerebri ruling out holoprosencephaly.

description

the cerebral hemispheres are virtually absent in hydranencephaly and are replaced by fluid-filled sacs lined by leptomeninges. the precise aetiology of hydranencephaly is still unknown, although the anomaly is thought to be the result of bilateral internal carotid artery occlusion. thrombosis and vasculitis is commonly found affecting smaller cerebral vessels in these infants, and other types of vascular disruption such as ileal atresia and renal agenesis can coexist. other reported associations include x-ray exposure, toxoplasmosis, rubella, herpes simplex infection, ingestion of estrogen during pregnancy, and butane gas intoxication.

diagnosis

a large cystic mass fills the entire intracranial cavity. macrocephaly is frequently noted. the falx may or may not be visualised. absence of the cerebral cortex together with the characteristic appearance of the brain stem protruding into the cystic cavity leads to the diagnosis. hydranencephaly may be seen in association with polyhydramnios or oligohydramnios. the former is considered a result of a depressed fetal swallowing reflex caused by hypothalamic injury, the latter by coexisting renal agenesis.

differential diagnosis

other causes of a large intracranial cyst require differentiation: it may be difficult to differentiate hydranencephaly from alobar holoprosencephaly. massive hydrocephalus and absence of the midline echo is consistent with both; however, no cortex will be discerned in hydranencephaly and it is usually possible to demonstrate at least a rim of frontal cortex in alobar holoprosencephaly. midline facial abnormalities (cyclopia, ethmocephaly) are not typical of hydranencephaly. in cases of massive hydrocephalus, the falx and cerebral cortex should be visualised, and the characteristic bulging of thalami and brain stem is not seen. similarly in porencephaly there are usually regions of cortical sparing which can be identified, despite other cerebral architectural derangement.

sonographic features

large empty cystic area within cranium.

no visible cerebral cortex.

thalami and brain stem bulge inside fluid-filled intracranial cavity.

macrocephaly.

falx may be absent.

associated syndromes

familial hydranencephaly
mbakop
proliferative vasculopathy
renal adysplasia
trisomy 13

references

edmondson sr, hallak m, carpenter rj, cotton db evolution of hydranencephaly following intracerebral hemorrhage hydranencephaly obstet gynecol 79: 870-871
lin y-s, chang f-m, liu c-h antenatal detection of hydranencephaly at 12 weeks menstrual age j clin ultrasound 20: 62-64
wheeler tc, dao a, jeanty p hydranencephaly fetus 1(2): 7423.1
belfar hl, kuller ja, hill lm, kislak s evolving fetal hydranencephaly mimicking intracranial neoplasm j ultrasound med 10: 231-233
persutte wh, lenke rr, derosa rt prenatal ultrasonographic appearance of the agnathia malformation complex j ultrasound med 9: 725-728
hadi ha, mashini is, devoe ld, holzman gb, fadel he ultrasonographic prenatal diagnosis of hydranencephaly j reprod med 31: 254-256
greene mf, benacerraf b, crawford jm hydranencephaly: us appearance during in utero evolution radiology 156: 779-780