24.1 Introduction

Resection or disconnection of an entire cerebral hemisphere, the most radical form of epilepsy surgery, is indicated when frequent and devastating seizures, originating from a widespread area or multiple foci within one cerebral hemisphere, cannot be controlled by medical treatment. The basic idea is to entirely disconnect the seizing hemisphere in order to enable the contralateral hemisphere to develop as normally as possible in order to preserve higher cortical functions and to ensure the best possible cognitive development of the child when performed early in life. The underlying pathology does not pose a diagnostic problem since it will be identified either on magnetic resonance imaging (MRI) or in association with the clinical evolution, the epileptic syndrome, and the electroencephalogram (EEG) findings. The crucial issues in the process of eligibility for hemispheric surgery are rather threefold:

1. 
   

   Can the extent of the epileptogenic cortex in one hemisphere be surgically efficiently treated by a less than hemispheric surgery, i.e., multilobar disconnection or resection, thus preserving significant cortical areas of the same hemisphere?

   
   
2. 
   

   If the answer is no, can we be sure that the opposite cerebral hemisphere is “sane,” i.e., not responsible for a part of the seizures? In other words, can we be sure that the opposite hemisphere will not be the origin of continuing seizures once the affected hemisphere is removed or disconnected?

   
   
3. 
   

   If this can be confirmed, in general by MRI and EEG recording of all types of presenting seizures, do we expect any deterioration in neurological functions (language, motor, visual) and to what degree, following hemispheric surgery?

The third question is certainly the most challenging and has to be decided based on the actual neurological status of the patient, the evolution and degree of deterioration in the past, supportive examinations such as functional MRI, especially for language tasks, or fiber tracking of the different functional pathways, in order to estimate the degree of asymmetry, lateralization, or impairment.

On the other side, the degree of neurological and cognitive deterioration under medical treatment alone should be anticipated as well when arguing against hemispheric surgery or considering postponing it for months or even years in order to be then confronted with less “functional sacrifice.” The most striking situation is residual language function in the affected hemisphere and the expected timing of interhemispheric language transfer. Could we decide for early surgery accepting postoperative aphasia, which will eventually recover to a certain degree over the following years? Or should we wait until evidence exists at some point in the future for bilateral or predominantly contralateral language representation, while accepting the possibly devastating and partly irreversible effects of seizures on higher cortical functions?

All these aspects have to be considered and discussed with the patient and his family, in order to decide if hemispherotomy will improve the patient’s situation at this particular moment or should be performed later.

24.2 Historical Background

In order to reduce the well-described major complications associated with the first-generation anatomic hemispherectomies from the 1950s on, ¹ Theodore Rasmussen applied the concept of cerebral disconnection in the surgical treatment of hemispheric epilepsy by proposing the functional hemispherectomy. ² He considerably reduced the amount of tissue resection by combining temporal lobectomy and perirolandic resection, in order to expose the entire length of the corpus callosum and the insular cortex, with subsequent disconnection of the frontal and parieto-occipital lobes including all white matter fibers. This major modification would reduce the amount of intraoperative blood loss and avoid late superficial cerebral hemosiderosis, while obtaining the same efficacy on seizure-free outcome.

The advent of Rasmussen’s functional hemispherectomy opened the door for the succeeding era of hemispherotomy techniques from the early 1990s on, all having in common to further reduce the amount of cerebral resection in favor of disconnection. ³

Two main approaches have developed almost in parallel: Delalande′s vertical transventricular hemispherotomy, ⁴ where he first suggested the term hemispherotomy, and Villemure’s lateral peri-insular hemispherotomy, ⁵ , ⁶ which appeared to be an evolutionary consequence of Rasmussen functional hemispherectomy. Later, Schramm et al presented the transsylvian “keyhole” approach, resembling Villemure’s lateral approach, while aiming to further minimize the amount of resection. ⁷

From the beginning on, only few publications have questioned the advantage of one approach over the others, since each center practicing hemispheric epilepsy surgery would present the results of their own technique. Published series and literature reviews comparing different types of functional hemispherectomy and different types of hemispherotomy did not find significant differences among them with respect to seizure outcome. ³ , ⁸ , ⁹

In this chapter, we will elaborate in more detail Delalande’s vertical parasagittal hemispherotomy (VPH). ¹⁰ , ¹¹ Since 1992, this technique has been used in almost 300 patients at our institution. The approach is presented in six consecutive steps, each composed of three types of data: a scheme emphasizing the objective of the specific step, representative intraoperative figures, and post-VPH MRIs (typically done about 3 months postoperatively) demonstrating the disconnection path of each step.

24.3 Description of the Surgical Technique of VPH

24.3.1 Approach to the Ventricle: Posterior Frontal Resection

(▶Fig. 24.1)

Under general anesthesia, the patient is placed supine, the head kept in a neutral, slightly flexed position in the pin head holder. Neuronavigation is not indispensable, but we have used it systematically over the last decade for teaching purposes. Furthermore, it can be particularly beneficial in children with hemimegalencephaly. In this setting, it helps to confirm anatomical landmarks such as the position of the interhemispheric fissure before craniotomy, which not always corresponds to the skull midline. It is also useful during the hemispheric disconnection since cerebral overgrowth, distortion of the midline structures, and a dysmorphic ventricle can render recognition of the landmarks difficult.

Following a longitudinal frontoparietal skin incision 1.5 to 2 cm from the midline, a paramedian craniotomy of about 3 to 4 cm width and 5 to 6 cm length is performed, about one-third in front of and two-thirds behind the coronal suture. In order to reduce the risk for intraoperative blood loss, attention should be given to preserve the bridging veins. Accordingly, a posterior frontal cortical resection of about 2.5–3 × 4–5 cm would spare the mesial cortex. An en bloc resection of the cortex and white matter is performed down to the roof of the central part of the lateral ventricle, and this specimen is preserved for histopathological examination. A progressive exposure of the intraventricular anatomy must allow the identification of three important structures: (1) the foramen of Monro (which should be occluded with Cottonoid once identified, in order to avoid blood spillage into the third ventricle; (2) posterolaterally, the floor of the ventricular atrium; and (3) just above the ventricular roof, the corpus callosum.

24.3.2 Posterior Callosotomy

(▶Fig. 24.2)

The objective of this step is to begin hemispheric disconnection from the posterior half of the corpus callosum (callosotomy). First, the pericallosal arteries below the cingulate gyrus must be clearly visualized as they will guide the midline route posteriorly toward the splenium and, in a later step (anterior callosotomy, see Section 25.3.5), in the opposite direction anteriorly toward the genu and rostrum.

For this reason, the microscope has to be tilted slightly medially and the ultrasonic aspirator is used for exposing these arteries just below the cingulum. As far as the midline callosotomy, our paramedian transventricular approach is anatomically more challenging than when performed through the interhemispheric fissure; however, as we stated above, this approach avoids injury to all bridging veins close to the superior sagittal sinus. In order to avoid contralateral ischemia, it is of utmost importance to avoid injury to the pericallosal arteries. It should be noted that in 4 to 12% of the patients, a single or a dominant pericallosal artery supplying both hemispheres may be present. ¹² , ¹³

As in corpus callosotomy performed through an interhemispheric approach, this callosal dissection over the midline will expose the interventricular septum pellucidum and the ependymal lining of the contralateral ventricle.

The callosotomy is pursued posteriorly toward and through the splenium. It is at this point that incomplete hemispherotomy may result if the splenium is not completely dissected until the arachnoid over the quadrigeminal cistern below and the vein of Galen just posteriorly.

Since the shape and thickness of the different parts of the corpus callosum can vary considerably, it should have been studied preoperatively on MRI.

Related posts:

21 Anatomical Hemispherectomy 19 Corpus Callosotomy 20 Endoscopic Callosotomy and Hemispherotomy: Bimanual Endoscopic Technique 22 Functional Hemispherectomy and Peri-insular Hemispherotomy 23 Endoscopic-Assisted Hemispherotomy 18 Cortical Disconnections

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