I would say of all the neurosurgical procedures I performed at the Hospital for Sick Children, the peri-insular hemispherotomy is among the most technically difficult and challenging. This is because of the requirement for a thorough understanding of the neuroanatomy involved, but also because of the pitfalls that may result from the challenging neuropathological conditions treated, such as hemimegalencephaly and hemispheric cortical malformations.