Objective To report two preterm siblings with antenatal development of an intraventricular and parenchymal haemorrhage with prenatal evolution into a porencephalic cyst on routine cranial ultrasound on admission.

Methods Family history was obtained. Thrombophilia and coagulation examinations, genomic sequencing of COL4A1 and ophthalmological examination were done in all family members. Family members bearing a COL4A1 mutation were seen by a developmental paediatrician and physiotherapist or a neurologist, and magnetic resonance imaging (MRI) examination of the cerebrum was performed.

Results During the first pregnancy, a mild abdominal trauma occurred at gestational age 23 weeks with subsequent abdominal pain and reduced fetal movements for 24 h. A boy was born at 33 weeks gestation. He eventually required a ventriculoperitoneal shunt for progressive ventricular dilatation. He developed a hemiplegia and mental retardation. His sister was born at 31 weeks gestational age. During this pregnancy the mother had premature contractions at gestational age 26 weeks. In the neonatal period a subcutaneous reservoir was inserted for ventricular dilatation which stabilised after 2 weeks. She is 2.5 months old and shows an abnormal tone pattern. Both siblings and their mother have a not previously described G1580R missense mutation in the COL4A1 gene, essential for the stable conformation of the vascular basement membrane. The mother does not show abnormal neurological signs, cataract or tortuosity of the retinal vessels. The MRI of her brain showed extensive white matter lesions without porencephalic cyst.

Conclusions Infants presenting with a porencephalic cyst and their parents should be examined for a COL4A1 gene mutation, if other causes are excluded.