|Year : 2008 | Volume
| Issue : 1 | Page : 107-110
Surgical procedures for intractable hemispheric epilepsy
Milind S Sankhe, Venkateswara P Govindappagari
PD Hinduja National Hospital and Medical Research Center, Mahim, Mumbai - 400 016, India
Milind S Sankhe
PD Hinduja National Hospital and Medical Research Center, Mahim, Mumbai - 400 016
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Objectives: To outline the evolution, indications, surgical techniques and complications of hemispheric procedures for intractable epilepsy. Materials and Methods: We review the patient selection, timing of surgery, surgical procedures and complications. Conclusions: There are clear indications for hemispheric procedures for intractable epilepsy, but the timing remains a concern in certain cases. The complications have reduced with the modified anatomical, functional and disconnective surgery with the improving surgical techniques.
Keywords: Intractable hemispheric epilepsy, surgical procedures, complications
|How to cite this article:|
Sankhe MS, Govindappagari VP. Surgical procedures for intractable hemispheric epilepsy. J Pediatr Neurosci 2008;3:107-10
| Introduction|| |
The first case of anatomical hemispherectomy was reported by Dandy  in 1928, to remove a diffuse hemispheric glioma. McKenzie  is credited to perform the first hemispherectomy to treat intractable epilepsy on an adult patient in 1938 with excellent results. The first series was reported in the year 1950 by Krynauw.  The patients showed remarkable recovery with marked reduction in seizure frequency and improvement in cognition, behavior and personality. The procedure gained popularity in the following decades with excellent results and acceptable mortality rates.  However, delayed complications such as hydrocephalus and superficial cerebral hemosiderosis were reported. Late deaths were attributed to these complications. , 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.
Despite various modifications, role of anatomical hemispherectomy continues to hold its importance, particularly for patients with hemimegalencephaly and diffuse hemispheric cortical dysplasia.
| Indications|| |
The typical candidates are patients with intractable epilepsy due to unilateral hemispheric cerebral pathology. These include congenital malformations such as Sturge Weber syndrome More Details [Figure - 1], hemimegalencephaly [Figure - 2], diffuse cortical dysplasia or acquired lesions such as Rasmussen encephlalitis. However, the most common pathology is perinatal infarct [Figure - 3].
Detailed clinical evaluation with documentation of hemiparesis and hemianopsia should be performed. 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 More Details 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 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. All vascular input and output must be interrupted, a complete callosotomy and the corona radiata sectioned superior and lateral to the thalamus. The remaining posteroinferior frontal cortex, as well as the medial temporal structures, is also excised. Complications encountered following this method of hemispherectomy have led many centers to abandon it in its original form and have attempted multiple modifications.
'Hemidecortication' described by Benjamin et al.  consists of removal of the whole cerebral cortex, with sparing of the white matter, thus avoiding opening of the lateral ventricle. This maneuver reduces the size of the hemispherectomy cavity created, minimizing the mixing of bloody material and debris from the surgery with the ventricular CSF. The 'modified hemispherectomy' as described by Adams  consists of an anatomic hemispherectomy followed by occlusion of the ipsilateral foramen of Monro with muscle to prevent communication between ventricular CSF and the hemispherectomy cavity. Additionally, the volume of the hemispherectomy cavity was reduced by tacking the convexity dura to the falx, the basal dura and the tentorium, thereby creating a large extradural space [Figure - 4].
'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.
Villemure et al.  described a technique where supra-insular and infra-insular windows are created, allowing access to the ventricle, through which the disconnections are made, amygdala and hippocampus excised and the insula disconnected at the end [Figure - 5].
| Complications|| |
Intraoperative complications involve fluid and electrolyte imbalances and bleeding. Significant blood loss is frequent, which can be problematic in young children, not only for perfusion but for clotting as well. Aggressive fluid, electrolyte and hemostatic management is absolutely necessary during these procedures. 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. Though uncommon, the presence of a large empty space following anatomic hemispherectomy has been suspected to favor the development of a hematoma even after minor head injury. Historically, the main late complication has been superficial cerebral hemosiderosis, initially described by Oppenheimer and Griffith;  its occurrence can be markedly reduced by minimizing access of blood and blood by-products to the ventricular system, early drainage using a ventricular catheter and decreasing ventricular exposure by decreasing the volume of the hemispherectomy cavity, e.g., functional hemispherectomy. Late-onset hydrocephalus has been the most significant complication, ranging from 17.6%  to 35.4%. 
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 development of obstructive hydrocephalus.  Late mortality may occur due to complications related to CSF pathways, e.g., shunt malfunction or superficial cerebral hemosiderosis.
Seven patients in age groups varying from four and half years to 17 years underwent hemispheric procedures done by the author. Two patients had Rasmussen's encephalitis, one patient presented with diffuse cortical dysplasia and four had perinatal infarct. One patient had peri-insular hemispherotomy, and the rest underwent functional hemispherectomy. There was no mortality. Average blood loss in the functional hemispherectomy was 400 ml; and in the patient with peri-insular hemispherotomy, 250 ml. One patient developed contralateral subarachnoid hemorrhage and swelling; shifting the midline structures to the side of surgery required ventilatory support for a week. Four patients developed postoperative fever secondary to aseptic meningitis.
In principle, whichever method of hemispherectomy is utilized based on the same indications, the resulting seizure control should be identical. These techniques, either by removal or disconnection, completely eliminate the epileptogenic influence of the diseased hemisphere, to result in a seizure-free or virtually seizure-free state. Failures in seizure control are due either to incomplete disconnection or bilateral foci.
| Conclusions|| |
Modifications to anatomical hemispherectomy were developed in response to complications, notably late-onset hydrocephalus and superficial hemosiderosis. Several techniques have been developed combining smaller resections, disconnections and callosotomy. Disconnective approaches are aimed at smaller exposure, lower blood loss, reduced complications and shorter hospital stay. However, these may not be ideal for hemimegalencephaly, in which there is an enlarged dysplastic hemisphere. Timing may be a concern in certain acquired progressive conditions, but in general early surgery is advisable in presence of inborn pathological substrates and clear ipsilateral deficit. The complications associated with hemispheric procedures have reduced with better understanding and improved surgical techniques.
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[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5]