Hemihypertrophy

Although 'hypertrophy' technically means enlargement of existing cells, the overgrowth in this condition results from increased cell number, so hemihyperplasia is now the preferred term; both appear in the literature and on examinations. The finding may involve a limb, the face, or an entire side and often becomes more apparent with growth. Its importance is entirely in the associations it flags. Beckwith-Wiedemann syndrome results from abnormal genomic imprinting at 11p15.5, most often loss of methylation at IC2 or paternal uniparental disomy, leading to overexpression of the growth factor IGF2 and loss of the growth suppressor CDKN1C. Affected infants require glucose monitoring for hypoglycaemia and airway assessment for macroglossia, and lifelong awareness of tumour risk. Tumour surveillance with three-monthly abdominal ultrasound and alpha-fetoprotein is standard in childhood. Leg length discrepancy may need orthopaedic management. Differential considerations include Proteus syndrome, neurofibromatosis type 1, Klippel-Trenaunay-Weber syndrome, and, on the opposite side of the problem, hemiatrophy from a neurological or vascular cause.