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Hemimegalencephaly (HME) is a rare neurological diagnosis defined as hamartomatous overgrowth of one cerebral hemisphere. The hypothesised pathogenesis is due to an increased number or size of neural cells; however, the exact mechanism can vary widely, depending on the underlying aetiology. We report a case outlining the prenatal diagnostic process and obstetric considerations for delivering an infant with HME secondary to megalencephaly-capillary malformation syndrome. After diagnosis, our patient was induced and delivered at 37 weeks of gestation via operative vaginal delivery. To our knowledge, this is the first report describing the course from prenatal diagnosis through delivery of a fetus with HME., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

Competing Interests: Competing interests: None declared.

Megalencephaly-capillary malformation-polymicrogyria syndrome (MCAP) is a rare disorder that arises as a result of a somatic mosaic mutation in the PIK3CA gene. It characteristically presents with postnatal or congenital megalencephaly, cutaneous capillary malformations, postaxial polydactyly and often segmental or focal body overgrowth. We report a 7-year-old boy with known MCAP who was diagnosed at around 10 months old with a mosaic change in the PIK3CA gene. He was found to have hall-mark clinical signs; macrocephaly and four-limb postaxial polydactyly. Since diagnosis, he has had multiple clinical features, most of which typically present in children with MCAP. He has now been diagnosed with autism spectrum disorder (ASD), demand avoidance and is under assessment for attention deficit hyperactivity disorder. Although some cases have been raised to the M-CM Network, to our knowledge this is the first case of ASD in MCAP to be reported in the literature., Competing Interests: Competing interests: None declared., (© BMJ Publishing Group Limited 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Competing Interests: Competing interests: None declared.