[[Functional hemispherectomy]]/[[hemispherotomy]] is a [[disconnection procedure]] for [[severe medically refractory epilepsy]] where the seizure foci diffusely localize to one [[hemisphere]]. It is an improvement on anatomical [[hemispherectomy]] and was first performed by Rasmussen in [[1974]]. Less invasive surgical approaches and refinements have been made to improve seizure freedom and minimize surgical [[morbidity]] and [[complication]]s. Key anatomical structures that are disconnected include the 1) [[internal capsule]] and [[corona radiata]], 2) [[mesial temporal]] structures, 3) [[insula]], 4) [[corpus callosum]], 5) [[parietooccipital connection]], and 6) frontobasal connection. A stepwise approach is indicated to ensure adequate [[disconnection]] and prevent seizure persistence or recurrence. In young pediatric patients, careful patient selection and modern surgical techniques have resulted in > 80% seizure freedom and very good functional outcome. 
Young et al. summarized the history of [[hemispherectomy]] and its development and present a graphical guide for this anatomically challenging procedure. The use of the [[osteoplastic]] flap to improve outcome and the management of [[hydrocephalus]] are discussed
((Young CC, Williams JR, Feroze AH, McGrath M, Ravanpay AC, Ellenbogen RG,
Ojemann JG, Hauptman JS. Pediatric functional hemispherectomy: operative
techniques and complication avoidance. Neurosurg Focus. 2020 Apr 1;48(4):E9. doi:
10.3171/2020.1.FOCUS19889. PubMed PMID: 32234987.
)).