Metabolic megalencephaly

Measuring the head circumference is an essential component of the physical examination in pediatric practice and in particular in neuropediatric assessment. The measurement of the head circumference is a challenge for pediatricians, as it is not easy to carry out in young children. Serial measurement of head circumference during every health supervision visit is necessary up to ۲۴ to ۳۶ months of age to assess head growth velocity. It is also critical to monitor head size frequently in high-risk cases such as preterm infants and those in the active phase of bacterial meningitis, subdural hematoma, and hydrocephalus. Macrocephaly, defined as a head circumference greater than ۲ standard deviations above the mean, is a relatively common presenting symptom in the pediatric population at routine well-child examinations and a common indication for neuroimaging. Macrocephaly is a relatively common clinical condition affecting up to ۵% of the pediatric population. It encompasses a broad range of clinical entities ranging from benign familial macrocephaly and Benign External Hydrocephalus (BEH) to more than ۲۰۰ genetic disorders. Metabolic megalencephalies result from cellular edema or abnormal accumulation of metabolic substrates within the neurons and glia secondary to an underlying biochemical defect (most commonly an enzyme deficiency), without an increase in cell number. Metabolic disorders presenting with increased head size have been classically divided into three major groups: organic acid disorders, lysosomal storage disorder, and leukoencephalopathies. A systematic approach which includes a thorough clinical history and physical examination are crucial in the evaluation of a child with macrocephaly. The first and most important step in the evaluation pathway of macrocephaly is the exclusion of raised ICP as it is a neurosurgical emergency. Diagnosis of metabolic megaencephalies is based on specific neurological features associated with the megalencephaly Familial history of similar disorders, consanguineous mariage, clearly progressive neurological impairment and Involvement of other organs (eyes, heart, spleen and liver, skin, and muscles). Laboratory findings and neuroimaging are mandatory for a diagnosis.