Fetal hydrocephalus often refers to an extension of fetal ventriculomegaly where the ventricular dilatation is more severe. It is usually defined when the fetal lateral ventricular diameter is >15 mm ¹.

Epidemiology

The estimated incidence is 0.5-3 cases per 1000 live births. There may be a very slight increased female predilection ¹¹.

Pathology

Fetal hydrocephalus can be either obstructive or non-obstructive and each can arise from a number of aetiologies. In a small proportion of cases, it carries a familial X-linked inheritance (congenital X-linked hydrocephalus).

Causes

• in utero infection(s)

Associations

The vast majority of conditions are associated with other intracranial and cranial anomalies ⁶. The list includes:

• central nervous system anomalies: (more common ⁷ and reported in >80% of cases)

  • aqueductal stenosis: one of the most common causative associations

  • Chiari malformations

  • neural tube defect(s)

  • Dandy-Walker malformation

  • encephalocele

  • alobar holoprosencephaly

  • posterior fossa cysts

  • polymicrogyria

• non-central nervous system anomalies

  • craniofacial

    • cleft lip +/- palate

    • low set ears

    • bilateral optic atrophy

    • facial bone anomalies

    • acrocephalosyndactylia

  • congenital cardiovascular anomalies

  • gastrointestinal anomalies

  • genitourinary anomalies

    • congenital renal fusion

  • skeletal anomalies

    • clubfeet

• syndromes

  • Meckel-Gruber syndrome ¹¹

  • Miller-Dieker syndrome ¹¹

• chromosomal anomalies: may be present in ~20% of cases ¹¹

  • trisomy 21 ⁸

  • triploidy ⁸

See also: congenital syndromes associated with enlarged ventricles.

Radiographic features

Ultrasound

Will demonstrate enlarged ventricles with variable degrees of parenchymal thinning. The choroid may be seen floating within the ventricle giving a dangling choroid sign. Often a separation of more than 3 mm between the choroid plexus and the margin of the ventricle is considered abnormal ^ref. In some cases, there may also be evidence of macrocephaly ^ref.

Treatment and prognosis

The overall prognosis will depend on the underlying cause and associated anomalies. Some cases can slowly progress during the fetal period. Antenatal shunting has been considered in a small proportion of selected cases ².