23.1 Introduction

Hemispheric disconnection is the preferred procedure for drug-refractory epilepsy due to unilateral hemispheric pathologies. ¹ , ² , ³ The fundamental approach includes either insular (lateral) or parasagittal (vertical) approaches, with many modifications described. ⁴ , ⁵ , ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁴ Endoscopic methods have been described recently. ¹⁵ , ¹⁶ , ¹⁷ , ¹⁸ , ¹⁹ , ²⁰ In 2015, the senior author (P. S. C.) described the first ever use of endoscopic-assisted interhemispheric hemispherotomy, which proved to be safe and effective. ¹⁸ , ¹⁹ More recently, he published a consolidated series of 32 cases and also described the utility of robotic assistance (ROSA; Medtech, Montpellier, France) in the use of the endoscopic technique. ¹⁵ Since then, this technique has become the preferred procedure at our institute. The reasons for its success are the following:

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  Improvement in endoscope and camera system has helped us to perform deep procedures and preserve critical structures, with minimal invasiveness.

  
  
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  Reduction of blood loss, preventing hypovolemia, is very important, since the majority of patients affected with these pathologies are children.

  
  
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  It is a disconnective procedure performed in deep in the surgical field and is thus easily performed by angling the endoscope (as described later).

23.2 Principles

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  First cadaveric description of endoscopic-assisted hemispherotomy was by Bahuleyan et al. ²¹ They made frontal and parietal burr holes to perform anterior and posterior disconnection, respectively. The procedure provided the idea of use of the endoscope for hemispheric disconnection but was difficult to translate for humans due to the approach through burr holes, difficult hemostasis, and possibility of suboptimal disconnection. We feel that the most important principle to be followed for performing this technique would be to have cisternal and ventricular access for hemispheric disconnection. One should access cisternal and ventricular spaces to drain cerebrospinal fluid (CSF) and make the brain lax, to create space, and also to have a proper anatomical perspective.

  
  
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  Hemostasis: In this procedure, one has to work in a limited space, and therefore adequate hemostasis is essential. Firstly, this demands a good bipolar, with variable impedance and nonstick technology. Secondly, longer instruments, i.e., bipolar forceps and suction cannulas, are required to work in the depth. Thirdly, high-definition endoscopic visualization is needed to see critical neurovascular structures.

  
  
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  Keyhole concept: One should know the concepts of minimal access surgery. Foremost of them is the keyhole concept. The approach should give an expanding cone area to access a wider area in the depth. ²² , ²³ The entry point should be placed in such a way that provides access from genu to splenium.

  
  
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  Anteriorly placed minicraniotomy: One has to make a cranial opening anterior to the coronal suture for two reasons. Firstly, it will provide equidistant access from genu to splenium of corpus callosum, which is important since we have to perform an interhemispheric complete callosotomy (▶Fig. 23.1). Secondly, it will prevent any bridging veins from coming into the path. This was the major reason Delalande preferred a transcortical route instead of an interhemispheric one. ▶Fig. 23.2 shows the traditional parasagittal approach with a craniotomy centered over the coronal suture. Wide separation of anterior and posterior limits of the working field can be appreciated, if compared to ▶Fig. 23.1.

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  CSF drainage and brain laxity: It is important to drain CSF from cisterns and ventricles to make the brain lax. Yasargil et al ²⁴ have emphasized gentle letting out of the CSF, which creates significant operating space. This method was found helpful in our experience to perform hemispherotomy even in nonatrophic cases like in hemimegalencephaly. Entering the ventricle also helps preserve the anatomical perspective.

  
  
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  Use of rigid endoscope holder: We emphasize the use of rigid endoscopic holding systems. Here, the surgeon has to work around critical structures in a controlled manner. Robotic devices like ROSA provide feedback to the surgeon while restationing the scope. This prevents sudden fall of weight over the surgeon’s hand, which prevents any injury to the critical structures, and reduces the fatigue to the surgeon. The principle is similar to the contemporary operating microscope in which there is protection against sudden fall of weight over the surgeon`s hand during the release of the magnetic locks. Devices such as a pneumatic endoscope holder (Point Setter holding system, Karl Storz, GmbH & Co. KG, Tuttlingen, Germany) could also be used.

  
  
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  Customized instruments:The authors prefer longer suction cannulas and bipolar forceps, as these help to reach distant targets such as the amygdala. Tapering detachable tips of suction cannulas help to adjust with the depth and corridor. Variable impedance and nonstick bipolar forceps are very helpful. Suggested options include Sutter Medizintechnik or Vesalius bipolar systems (Medilife Technologies). The authors believe that these are mandatory, and not luxury items as tissues of different densities like the gyrus rectus, insula, basal nuclei, and lenticulostriate arteries have to be approached. Similarly, a single-channel bipolar can be used, and it is quite helpful in narrow corridors.

23.3 Surgical Technique

Presurgical workup ¹⁵ , ¹⁹ , ²⁵ : It includes clinical semiology, magnetic resonance imaging (MRI) using an epilepsy protocol, and a video electroencephalogram (VEEG), which has recorded several seizures. In the absence of discordance between these, advanced investigations like single-photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetoencephalography (MEG) may be performed. ²⁶ However, the latter are rarely required for hemispherotomy. Functional MRI (fMRI) can be performed to search for language, motor, visual, and memory functions. ²⁷ , ²⁸ This may be performed especially for adult cooperative patients, in whom hemispherotomy is being contemplated on the dominant side. At our center, all patients undergo a comprehensive discussion in an epilepsy surgery meeting to discuss the battery of investigations needed and their results, generate a hypothesis, and formulate a decision plan. These meetings include epileptologists, epilepsy surgeons, neuroradiologists, nuclear medicine specialists, fellows, PhD students, and residents.

Presurgical counseling: This is very important as parents need to understand the expected outcomes of this procedure. We explain them that immediately following surgery, the patient may become hemiplegic and, following require extensive physiotherapy, this would improve, barring the pincer grip. Patients may have to be kept on ventilatory support for few days, especially in children with severe cognitive problems.

Radiological classification: From a practical perspective, we have divided the pathology into atrophic and nonatrophic ones. Atrophic ones had (1) sulcal widening, especially sylvian, (2) ipsilateral lateral ventricle and temporal horn dilation, and (3) porencephalic cysts. Nonatrophic ones included hemimegalencephaly, hemispheric cortical dysplasia, Rasmussen syndrome without cortical atrophy, and Sturge–Weber disease. This classification is useful, as patients with atrophic pathology are easier to operate on, and are better to do in the initial stages of learning curve.

Technique (see ▶Fig. 23.3, ▶Fig. 23.4, ▶Fig. 23.5, and Video 23.1) ¹⁵ , ¹⁷ , ¹⁸ , ¹⁹ : The patient is given general anesthesia. He/she is kept in a supine position with the head flexed 15 to 20 degrees. A minicraniotomy is planned centered 1 cm anterior to the coronal suture. Bridging veins are avoided with the use of neuronavigation. A transverse skin incision 5 cm in size is made over the intended center of the craniotomy, crossing about 2 cm across the midline. A 4 × 3 cm (sagittal X coronal) bone flap is elevated on the ipsilateral side. The sagittal sinus is not required to be exposed. A dural flap is elevated in a C-shaped manner with its base toward the sinus. At this point, the endoscope is brought in. We use a 30-cm-long, 10-mm-wide endoscope (Karl Storz, Tuttlingen, Germany) attached to a high-definition camera, and a light source. The authors prefer to stabilize this on a Robotic device (ROSA). This device also doubles up as a neuronavigation tool. The first thing to perform would be to visualize any bridging veins under the edges of the dura. If there are any bridging veins, especially anteriorly, they are coagulated and cut to prevent their sudden snapping during retraction. With the concept of keyhole surgery, retraction is performed more at the depth and less at the surface. Thereafter, a Leyla retractor is applied on the ipsilateral hemisphere, the interhemispheric fissure is entered, and its cistern is drained. With gentle CSF drainage, the brain becomes lax, and provides more and more space. With this continuing drainage, the brain opens like a “book,” and the corpus callosum comes into view. The pericallosal arteries are then separated (see Video 23.1).

This procedure has four basic steps: (1) corpus callosotomy, (2) anterior disconnection, (3) middle disconnection, and (4) posterior disconnection (▶Fig. 23.6 and ▶Fig. 23.7).

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  Corpus callosotomy: The authors first expose the corpus callosum from genu to splenium, and then split it from the splenium to the genu, to expose and cut the curving splenial fibers first. It is important to enter into the ipsilateral ventricle to prevent any injury to the septum and contralateral side. The genu must be sectioned until the level of anterior commissure.

  
  
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  Anterior disconnection: After corpus callosotomy, the anterior cerebral arteries (ACAs) are separated, and the gyrus rectus is resected anterior to the anterior communicating artery complex. This is begun at the junction of the genu and ACAs in the extraventricular plane, in order to avoid injuring the deep diencephalic nuclei. The disconnection proceeds laterally to enter the ventricle curving around the caudate head until the level of sphenoid ridge. This disconnection is done in the coronal plane. The arachnoid is visualized at the posterior part of the anterior cranial fossa, and this completes the anterior disconnection.

  
  
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  Middle disconnection: Thereafter, dissection is brought intraventricularly again. It proceeds in the sagittal plane, curving around the thalamus about 2 to 3 cm deep until the atrium. The choroid plexus is then followed and the temporal horn is entered. The senior author (P. S. C.) has found this technique useful, particularly in difficult nonatrophic cases. Otherwise, in the superior plane one can keep excising the insula and enter the temporal horn. Ventral amygdala resection is important to have complete disconnection, because it connects with the dorsal amygdala which is, in turn, connected with the deep diencephalic nuclei. The middle disconnection involves cutting of the lenticulostriate arteries, which causes mild bleeding. It is at this point that variable impedance bipolar coagulation is important as these tissues are quite dense.

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  Posterior disconnection; It involves cutting the hippocampal tail and fornix between the choroid plexus and splenial fibers, at the level of atrium. One should go under the splenium to effect complete disconnection. The arachnoid plane over the galenic venous system should be preserved.

Following hemostasis, an external ventricular drain (EVD) is left in the operative cavity for 48 to 72 hours. The cavity is filled with saline to prevent pneumoencephalus. The dura is closed primarily, the bone is placed back, and the wound is closed in a standard manner. We perform a CT scan within 4 hours after surgery. If available, intraoperative MRI may be performed to confirm complete disconnection. Otherwise, it can be performed at 3 months and 1 year of follow-up. This is important as some cases may develop late hydrocephalous due to deafferentation atrophy of the disconnected hemisphere.

Postoperative care: Antibiotics are given for initial 5 days. EVD should be removed as soon as the CSF becomes clear of blood. We have found that about 30% of patients have fever for the initial 5 to 7 days, even in the absence of infection. This may be due to thermogenic effects of blood byproducts. This is managed with acetaminophen, cold sponging, and, if required, propranolol. Recently, we have also found bromocriptine useful to control pyrexia of central origin.