hemihyperplasia

The term hemihyperplasia has replaced hemihypertrophy because the abnormality is an increased number of cells, not enlargement of individual cells. It may be isolated or syndromic. Beckwith-Wiedemann syndrome, caused by dysregulated imprinting at chromosome 11p15.5 involving IGF2 and CDKN1C, presents with macrosomia, macroglossia, omphalocele or umbilical hernia, organomegaly, neonatal hypoglycaemia from islet cell hyperplasia, ear creases and pits, and hemihyperplasia. The clinically critical consequence is a markedly increased risk of embryonal tumours, above all Wilms tumour and hepatoblastoma, and also adrenocortical carcinoma, neuroblastoma, and rhabdomyosarcoma. Surveillance is therefore recommended: abdominal ultrasound every three months until around age seven or eight, plus serum alpha-fetoprotein every three months until about age four for hepatoblastoma. Other syndromes with asymmetric overgrowth include Proteus syndrome, Klippel-Trenaunay, and Sotos syndrome. Isolated hemihyperplasia carries a lower but still real tumour risk and warrants similar screening.