20.1 Evolution of Endoscopic Surgical Techniques

Use of a channeled endoscope was popularized by urologists for obtaining biopsies, fulgurating bleeding tumors, or removing bladder stones. The technique was then adapted by the gynecologist for endoscopic tubal ligations and later applied to vaginal hysterectomies.

A channeled endoscope, however, has limited ability to permit bimanual dissection of tissues in more complex operations. This is because an instrument introduced through the channel can be moved only along the axis of the channel or rotated along its axis. The use of channeled endoscopes in neurosurgery has, therefore, been limited to intraventricular surgery, such as third ventriculostomy, biopsy, or suction removal of small intraventricular lesions. The hesitation to use endoscopes for larger lesions relates to the inability to bimanually dissect, visual obscuration from blood in the field, and difficulty in obtaining controlled coagulation.

The concept of three-port surgery, where the endoscope is introduced through one port and two other instruments through two separate ports, was introduced for laparoscopic cholecystectomies. It allowed bimanual dissection and ability to safely control bleeding or ligate vessels. This concept has advanced to more complex abdominal operations in the last decade and has been adapted for transsphenoidal neurosurgical operations. The endoscope is placed through one of the nostrils and is held by an assistant, fixed on a holder or on a robotic arm. The surgeon operates using instruments introduced into the field through each of the nostrils. A similar arrangement using a ventriculoport system has been used for deep-seated brain tumors and also for spine surgery using tubular retractors with or without an endoscope. In these approaches, if the field of surgery is small, the endoscope requires little manipulation once fixed in position. On the other hand, if the field of surgery is large, such as in hemispherotomy, the endoscope may require frequent repositioning by repeatedly unmounting and refixing it. Another major limitation of this approach is that the instruments cannot be seen unless they reach beyond the tip of the endoscope. This means that the surgeon has to take his eyes off the display and directly look at the field every time the instrument is to be reinserted into the field once withdrawn. Finally, with this approach there is crowding of the instruments, reduced working space, and need for a larger opening. This is because the three instruments, the endoscope and two working instruments, are triangulated through the same opening.

To circumvent these disadvantages, the authors utilize an endoscope to which a rigid suction is attached which projects about 2 cm beyond the tip of the endoscope. The surgeon uses this combo, holding it in left hand just like in conventional surgery and a second instrument such as a bipolar or dissector in the right hand to perform surgery. Since the endoscope is attached to the suction, it moves with the suction to the field of surgery, obviating the need for a holder, robotic arm, or an assistant to guide the endoscope to the field of surgery. We have initially described the use of this method for transcallosal resection of intraventricular tumors ¹ and subtorcular resection of pineal region tumors. ² Cutler et al ³ applied such a system using a custom-made endoscope for evacuation of intracranial hematomas and reported its use for vestibular neurectomies and endoscope-assisted aneurysm clipping.

Our experience suggests that working at such a depth with a 2D endoscope is often challenging. With experience, one can learn to judge the depth in 2D cases, using visual and motion cues from surrounding structures. However, this may not be an optimal or a safe method of operating. Recent availability of a lightweight single-chip 3D endoscope (VisionSense) offers the advantage of depth perception and improves the ease and comfort of operation. One of the drawbacks of the current system is limited color spectrum. While adjustment on the display and different options for improved color perception can enhance the color, it takes away the color discrimination between tissues to some degree. Despite this shortcoming, use of a 3D endoscope, where available, is preferable to 2D endoscopes.

20.2 Equipment/Medications

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  Three-dimensional 4-mm rigid endoscope (VisionSense) with metal irrigation sheath (▶Fig. 20.1).

  
  
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  Frazier suction extended 2 cm beyond the endoscope with coupling device.

  
  
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  Bipolar and endoscopic bipolar (Karl Storz GmbH & Co, Tuttlingen, Germany).

  
  
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  Neuronavigation system.

  
  
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  Cavitron ultrasonic aspirator (CUSA Integra).

  
  
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  Mannitol (20%, 1 g/kg body weight) is infused at the time of induction to provide optimum relaxation of the brain.

20.3 Anterior Interhemispheric Endoscopic Complete Callosotomy: Precoronal

The patient is positioned supine on the operating room table and the head is fixed in pins at roughly 20-degree flexion (▶Fig. 20.1a). Utilizing neuronavigation, a 2- to 3-cm precoronal suture midline incision is planned (▶Fig. 20.2a), avoiding large bridging veins on contrast magnetic resonance imaging (MRI). A 3-cm-diameter Alexis wound retractor (Applied Medical, Rancho Santa Margarita, CA) can be utilized for scalp retraction (▶Fig. 20.2b). The endoscope is then registered on the neuronavigation system for guidance.

A burr hole is made on the midline, and using Midas Rex footed burr, a 2- to 3-cm craniotomy is done on the right side. A dural flap is created and based medially on the sinus. The interhemispheric dissection is performed with the endoscope (▶Fig. 20.2c) or directly under loupe magnification to reach the corpus callosum. This dissection can be quite challenging with a 2D endoscope and even with a 3D endoscope; this requires experience. It is easier to do this step under loupe magnification until corpus callosum is reached (▶Fig. 20.2d). A folded cotton patty is placed in the anterior and posterior part of the craniotomy between the falx and the hemispheres to the level of the corpus callosum to maintain retraction on the hemisphere and to make the corridor for surgery. A Budde halo retractor system (Integra) can be utilized with a 3/8th retractor on the ipsilateral cerebral hemisphere, more for protection than retraction.

From this point onward, the endoscope that is attached to the suction is used in the left hand. Since the endoscope is attached to the suction, the two devices move as one and allow a two-hand technique in which the other hand can utilize an ultrasonic device or bipolar. With a bipolar or forceps, the two anterior cerebral arteries (ACAs) are dissected from each other for about 2 cm to expose the corpus callosum. The endoscopic callosotomy can be performed with suction, bipolar, or ultrasonic aspiration. The callosotomy is commenced in the midline frontally on the body of the corpus callosum. Full-thickness callosotomy should be performed to visualize the septum pellucidum and define the midline. The callosotomy is carried forward to the genu following the midline defined by the septum (▶Fig. 20.2e). At this point, the corpus callosum from the genu to the rostrum is removed (▶Fig. 20.2f). This step may require separating the two leaves of the septum pellucidum to access the rostrum. The ACAs may be seen in the interhemispheric fissure below the corpus callosum at this point. The anterior commissure can be sectioned anteriorly under the rostrum by following the ACAs.

We then work more posteriorly along the body again, staying strictly in the midline following the groove of the septum (▶Fig. 20.2g). The head of the operating table may have to be lowered to provide the optimum angle for surgery to reach the splenium. The callosotomy in the posterior part is essentially intracallosal (▶Fig. 20.2h) and the ACAs are above the site of resection. Once the splenium is removed, the vein of Galen may be visualized through the arachnoid of the pineal cistern (▶Fig. 20.2i). The resection is then carried forward to remove the inferior-posterior part of the callosum until the junction of the fornixes is reached by removing the fornical commissure.

It helps to work from the patient’s right when removing the posterior callosum and look at a monitor placed near the head on the left, as opposed to working on the anterior corpus callosum, where one looks at a monitor at the foot end of the operating table. Hemostasis is secured if needed with bipolar, endoscopic bipolar, or Surgicel. The dura is closed in a watertight fashion and the bone flap reapproximated. The skin is closed with absorbable suture. Intraoperative electroencephalogram (EEG) recording is obtained to look for desynchronization at completion of disconnection. See Video 20.1 and Video 20.2.