Removal/Disconnection of malfunctioning one half of the brain is known as hemispherectomy/hemispherotomy. McKenzi is credited to perform the first hemispherectomy to treat intractable epilepsy on an adult patient in 1938 with excellent results. The procedure gained popularity in the following decades with excellent results and acceptable mortality rates.
Rasmussen suggested modifications by removing only certain portions and disconnecting the remaining cortex, which was left in situ. The goal was to reduce the subdural cavity, thus reducing the risk of hemorrhages. Various modifications have been suggested aimed at preservation of the cortex with disconnection, hence reducing the risk of complications.
Indications
The typical applicants are patients with stubborn epilepsy due to autonomous hemispheric cerebral pathology. These include congenital malformations such as Sturge-Weber syndrome, Hemimegalencephaly, diffuse cortical dysplasia or acquired lesions such as Rasmussen encephlalitis. However, the most common pathology is perinatal infarct.
At Jaslok hospital, detailed clinical evaluation with documentation of hemiparesis and hemianopsiaperformed. Bilateral pathology or deficits predicts poor seizure-free outcome. Detailed imaging and electrophysiology will help predict the outcome. In certain cases where bilateral pathology is noted, improvement may still be noted in patients who undergo the procedure on the worst side. From the standpoint of producing a neurologic deficit, it is often already achieved by the disease process. In a progressive condition, such as progressive chronic encephalitis (Rasmussen’s), extensive Sturge-Weber syndrome and infantile spasms, in which continued clinical deterioration leading to a maximum contralateral neurological deficit is expected, early hemispherectomy may cause an acute worsening of the neurological deficit, but not worse than that to be produced by the disease process. The improved seizure control and psychosocial improvement following successful surgery outweigh the poor prognosis associated with the natural history of these disease processes, which are progressive and uniformly refractory to medical therapy.
Timing of Epilepsy Surgery
If proof of unilateral hemispheric damage is found, then the timing is determined by the severity and the age of the patient. Hemispheric procedure in the second or third year of life does not carry any risk of increased deficit and hence ideal for patients who come at early stages for diagnosis and evaluation. In late onset cases such as Rasmussen’s encephalitis, timing is controversial; as language and motor function transfer is less likely in older children. Evidence is accumulating that seizures themselves as opposed to the pathological substrate may significantly delay the cognitive development. Timing of surgery, to a great extent, depends on the severity of the epilepsy, natural history of the disease, adequacy of therapeutic medical trial. In certain conditions which are inborn, such as hemimegalencephaly and diffuse cortical dysplasia, very early surgery may be optimal.
Surgical Techniques
The surgical techniques of hemispherectomy have been historically classified into two main categories: the classic ‘anatomic hemispherectomy’ with its variations and the functional hemispherectomy. The anatomic hemispherectomy has had multiple modifications to decrease the complication rate, more specifically from superficial cerebral hemosiderosis and hydrocephalus. The functional hemispherectomy, initially described by Rasmussen and more recently modified by Villemure, minimizes the resection of tissue and has been shown to likewise further reduce the long-term complications.
The anatomic hemispherectomy simply consists of the removal of the cerebral hemisphere without the basal ganglia. The procedure may be done either en bloc or in multiple lobectomies, depending on the surgeon’s preference. Complications encountered following this method of hemispherectomy have led many centres to abandon it in its original form and have attempted multiple modifications.
‘Functional hemispherectomy’ is more widely used presently and consists of an anatomically subtotal, but physiologically complete, hemispherectomy. The operation is based on principles of disconnection rather than excision. The originally described method requires the excision of the central frontoparietal cortex, including the parasagittal tissue from the level corresponding to the genu of the corpus callosum to the splenium; a temporal lobectomy with an excision of amygdala and hippocampus; disconnection of the residual frontal and parieto-occipital lobes medially; a corpus callosotomy and an insulectomy.
Complications
A frequent postoperative complication following hemispherectomies is persistently elevated systemic temperature for 8-12 days postoperatively, which is likely to be secondary to the blood products entering the CSF. Early postoperative brain shift, with herniation and death, has been reported following anatomic hemispherectomy. Hydrocephalus in the early postoperative period, not related to superficial cerebral hemosiderosis has been reported in 7.5-10.5% of patients.
Late postoperative complications include infections and spontaneous and posttraumatic hemorrhages. The hemispherectomy-associated mortality was reported in a range between 1 and 6.6% however; in the recent series, this is closer to the lower end. Mortality is usually related to uncontrollable intraoperative blood loss and with the development of obstructive hydrocephalus.
At the Jaslok Hospital, we perform hemispherotomy in all patients with hemispheric dysfunction. In a carefully selected patient population, the seizure freedom has been almost 100%. We have had no operative or perioperative deaths. There has not been a single case of postoperative increase in the neurological deficit.