Indication and Presurgical Evaluation

The classic indication is for patients with severe hemispherical damage and drug-resistant epilepsy or drug-resistant epilepsy in early infancy known as catastrophic epilepsy. These patients usually are children or adolescents; in adults the procedure is performed les frequently.

This procedure is possible because these patients usually already have spastic hemiparesis, frequently partial hemi-anopia, and transferred of motor and language functions to the other (healthy) hemisphere either induced by the disease process or by the connatal condition. Diagnoses typically found in these patients may be classified into inborn, perinatal, or acquired conditions. In our series, these include intrauterine hemorrhages or perinatal injuries with brain defects (n = 38); multilobar cortical dysplasia, polymicrogyria, and other disorders of gyration (e.g., lissencephaly; n = 8); and hemimegalencephaly (n = 9). Other entities may present as progressive clinical pictures, like Rasmussen encephalitis (n = 10) or Sturge-Weber syndrome (n = 4)8 ( Fig. 28.1 ). Rarer acquired lesions include posttraumatic or postencephalitic hemispheric damage (n = 8), hemiatrophy (n = 3), and hemi-convulsion-hemiplegia-epilepsy syndrome (n = 1).

The indication is unproblematic if hemispheric damage is either congenital or occurred perinatally. An increase in the motor deficit usually is unlikely if the hemispheric damage happened in the first 3 years of life; here frequently only the fine pincer movements between index finger and thumb are lost postoperatively. Performing this surgery in children with a progressive disease that started to develop after the fourth year of life may be more difficult, although we have seen an initial postoperative deterioration of motor abilities in children between 4 and 8 years. A deterioration in motor function of the leg is usually transient. These children usually regain the ability to walk but frequently loose not only the pincer function between thumb and index finger but also grip function of their hand on the affected side. Deciding to perform hemispheric deafferentation in a progressive disease, such as Rasmussen’s or Sturge-Weber, is made somewhat easier by the knowledge that these children will be progressively impaired by the epilepsy disorder itself eventually with the same type of deficit after a few years as to be expected from the surgery, with the additional damage to their functional and cognitive development by the affection of the healthy hemisphere.

Presurgical evaluation always tries to demonstrate that the disease process is limited to the abnormal hemisphere. Electroencephalography (EEG) studies consist of interictal and ictal video-EEG. In planned hemispherectomy cases, it is not important to localize ictal activity to certain areas of the affected hemisphere but, if possible, to lateralize it only to the affected side. In our experience, the use of invasive recordings in these patients is rarely necessary. The presence of epileptic EEG activity in the contralateral healthy hemisphere as observed in a minority of these cases is said to indicate a lesser chance for seizure freedom9; however, this does not exclude the chance for seizure freedom after hemispherical deafferentation.10 In one large series, 77% of those with suspected bilateral disease were either seizure free or had only “minor events.”11 Independently arising seizure activity from the healthy hemisphere clearly discernable from the EEG activity and the ictal picture originating from the affected hemisphere may be considered as a relative contraindication for surgery. When seizure activity is observed in the so-called healthy hemisphere only during seizure activity recorded from the affected hemisphere, the interpretation is more difficult; here one should keep in mind that even a marked reduction in seizure activity after surgery is considered worthwhile by the families and the patients and may open the door for successful drug treatment, keeping in mind that there is a chance of perhaps 30 to 50% of seizure freedom despite the contralateral seizure activity in the EEG.

Of the various imaging modalities, the most important is magnetic resonance imaging (MRI), with computed tomography (CT) being mostly useful to demonstrate calcifications as in Sturge-Weber syndrome ( Fig. 28.1 ). The value of MRI is particularly important for suspected malformations of cortical development. Disorders of gyration, irregularities orthickening of the cortical band, gross malformations of the brain, and ectopic gray matter are characteristic findings. Atrophy, ventricle size, hemispheric configuration, widespread posttraumatic or postencephalitic damage, as well as more subtle regional atrophy in the early stages of Rasmussen’s may be demonstrable. In acute encephalitis and Sturge-Weber syndrome postcontrast MRI will show typical findings. In case of suspected Rasmussen encephalitis, it frequently is very helpful to carefully look at sequential MRIs over time, checking for developing atrophy and signs of regional in-flammation.

In our hands positron emission tomography or single photon emission computed tomography is rarely indicated in these patients. The intracarotid amobarbital test (Wada test) is still used in unclear cases to lateralize language function or to demonstrate complete transfer of language function. To use functional MRI (fMRI) for speech localization is not as reliable, because it has been demonstrated in chronic epilepsy patients, that incorrect or unclear localization may occur in up to 28% of patients.12,13 Neuropsychological assessment is performed as usual or as far as mental retardation allows.

The diagnosis of suspected Rasmussen encephalitis is not always that clear. If there is concern about the diagnosis, open brain biopsy, usually in the F1-gyrus though a fronto-dorsal-paramedian approach, is performed, delivering a tissue sample of 1 x 1 cm, without prior coagulation of the arachnoid, comprising pia mater, cortex, and white matter.

Advantages and Limitations of the Transsylvian Keyhole Deafferentation

Points that speak for this less invasive technique of transsylvian transventricular deafferentation are the proven reduction in blood loss, the reduced need for blood transfusion, and the reduction in operating room time.14 Shimizu and Maehara,5 Kestle et al,15 and Cook et al7 also demonstrated reduced need for blood replacement for their related techniques. The keyhole technique is well suited for hemispheres with large perinatal infarctions or large cysts in the territory of the middle cerebral artery (MCA), patients with enlarged ventricles, and patients with atrophic brains with a smaller-than-usual central bloc of insula-basal ganglia. The transsylvian transventricular approach is more difficult in hemimegalencephaly cases. The opercula may be much thicker, the configuration of the sylvian cistern is generally atypical, and thus orientation is much more difficult. One can still use the transsylvian transventricular deafferentation procedure in these cases; however, it is then advisable to combine it with a resection of the operculum, exposing the circular sulcus and facilitating the entry into the ventricle considerably. This was done in seven of nine hemi-megalencephaly cases of our series. One possible benefit of the keyhole technique, where the opercula are reflected and preserved compared with the perisylvian window tech-niques4,5,7 in which they are resected, is that hardly any MCA branches and large sylvian veins have to be resected and there is a lesser chance for postoperative swelling because of circulation disturbances. Conversely, there may be some swelling from the manipulation of the operculum.

The limits of this approach include its limited applicability in hemimegalencephaly and the difficult anatomical orientation with an inherent risk of incomplete disconnection. So far, we have not observed a case of incomplete disconnection toward the midline or the fronto- and occipito-basal arachnoid, but we have seen a few cases in which the fronto-basal anterior disconnection line was not ideally placed as far posterior as the level of the anterior cerebral artery but slightly anterior to it.16 Other authors have observed incomplete disconnection rates of 7, 19, 21, and 54%, even in Rasmussen-type surgeries.17–20

The high shunt rates known from anatomical resection do not seem to be reached by the transsylvian keyhole technique and related perisylvian or transventricular techniques. A certain percentage of shunt implantation appears unavoidable with all kinds of intraventricular procedures, as well as with these hemispherectomies. In more than 75 transsylvian procedures with 81 months mean follow-up on 56 transsylvian keyhole deafferentation procedures, we had 4 cases of hydrocephalus (5.4%), with only 2 of them needing a shunt (2.7%). The other 2 had cysto-ventriculostomy but no shunt. Shunt rates in related procedures5,20,21 were 10/53 for Delalande’s technique (19%), 5/63 for Villemure’s peri-sylvian window technique (8%), 5/22 in the Cleveland series (23%), and 5/32 for Shimizu’s and Maehara’s series (16%). In the review of the Los Angeles series7 in which three operation types were compared, the advantages of Mathern’s modification of the peri-insular surgery variant are listed as: least operative blood loss, least overall complication rate, and even a greater seizure-free outcome rate. A brief review of the pros and cons of this procedure is given in recent book chapters.22,23 A comparison of surgical techniques is given in Schramm 200216 and in adjoining chapters of this book.

Presurgical Management

The anticonvulsive medication is not withdrawn preoperatively. The laboratory evaluation includes the usual serum parameters including coagulation parameters and blood typing. Dexamethasone is given only preoperatively if a near normal or hemimegalencephalic brain volume is present, not in atrophic brains with large cysts or huge ventricles. Before skin incision, a prophylactic antibiotic is given. Two intravenous lines and one arterial line are placed; a central venous line is placed only in very small babies. After placement of a transurethral catheter, the patient is wrapped up carefully and kept warm using a Bair Hugger (Arizant Healthcare, Inc., Eden Prairie, MN).