33 Endoscopic-Assisted Resection of Intra-Axial Brain Tumors

10.1055/b-0036-142008

33 Endoscopic-Assisted Resection of Intra-Axial Brain Tumors

Luiz Carlos de Alencastro, Ademir Lodetti, Luiz Felipe de Alencastro, and Mário de Barros Faria

33.1 Introduction

The neuroendoscopic techniques have evolved considerably in the past 20 years, from fully endoscopic to endoscope-assisted surgeries. After the initial development of purely ventricular endoscopic approaches, neurosurgeons have expanded use of the endoscope to nonventricular pathologies and developed cisternal procedures (i.e., for tumors or cysts) and endonasal procedures.1

In recent years, the application of neuroendoscopic techniques has expanded to the resection of solid intraparenchymal lesions, especially intracerebral hematomas. In fact, Oi1 in 1999 had already observed that approaching deep-seated lesions would be a realistic indication for neuroendoscopy in the future.2,3,4

For selected cases, the endoscopic approach to intraparenchymal brain tumors allows the surgeon to choose a shorter route and do less retraction of the brain. Furthermore, this technique reduces the incision and damage to the skin, bone, and dura mater, minimizing surgical time and costs due to opening and closing of surgical wounds.

In this chapter we will discuss the indications for and limitations of the role of neuroendoscopic techniques in the approach to solid intraparenchymal brain tumors.

33.2 Indications/Contraindications

The endoscopic approach to brain tumors is indicated for patients with almost any kind of intraparenchymal lesion, but especially for those patients with deep-seated ones, excluding those lesions with wide cortical extensions (Fig. 33.1).

**Fig. 33.1** A 16-year-old male patient presenting with a large fronto-insular glioma with intense gadolinium enhancement. One year ago he submitted to a pterional approach in another institution, and grade II astrocytoma was diagnosed. Now he has come to our department with progressive headaches. **(a)** Axial magnetic resonance image (MRI): The *blue area* represents the frontal speech area demonstrated in functional MRI. The *red area* identifies the posterior limb of the internal capsule. **(b)** Sagittal MRI: the *yellow arrow* points to the middle cerebral artery and its intimal relation with the tumor.

Microscopic microsurgery has been the gold standard for resection of brain tumors. For this purpose, a large enough corridor must be created to allow instruments and light to get to the target area. Most times this will be achieved through brain retraction, extensive cisternal dissection, and bone drilling. Some authors5,6,7 reported the incidence of brain injury due to retraction ranging from 5 to 10%. Conversely, the main goal of microscopic microsurgical procedures is to minimize retraction of neurovascular structures.8,9

Brain retraction, especially when treating intraparenchymal tumors, is almost always necessary to different extents, and that is the importance of endoscopic techniques in this context. The ability of endoscopes to drive illumination and vision into the area of interest and the possibility to work with instruments within a very narrow corridor with less brain retraction is the key advantage of endoscopic techiniques.9

Even in cases where retraction may not be an issue, the deeper the lesion, the more difficult it is for the microscope to deliver good illumination in the operative field and, consequently, visualization worsens. Since an endoscope delivers light from its tip directly in the target area, much clearer visualization can be achieved.

Another possible indication for endoscopy in intraparenchymal lesions is the difficulty of avoidance of eloquent areas of the brain through traditional approaches. Some lesions are surrounded by eloquent brain tissue, hindering a direct transcortical approach. In this situation, use of an endoscope makes planning and executing a safer trajectory through the brain feasible. Sometimes longer intraparenchymal trajectories are necessary, but this may be less harmful to eloquent brain tissue.2,3,4

Kelly in 2004,10 even when working with the microscope, had already pointed to the advantage of creating a working channel with progressive dilatation of brain parenchyma, minimizing brain trauma. Although for that technique, it would have been necessary to have a 20-mm–wide channel so that light could reach the working zone. This microsurgical technique was modified by Ogura and described as the transcylinder approach. A piece of 0.1-mm transparent polyester film was used to create a cylindrical surgical route. The film was rolled into a thin stick and used to penetrate the brain under direction of a computer-aided navigation system. This technique was employed in 11 cases. By avoiding unnecessary retraction of brain tissue, it significantly reduced the risk of injury to surrounding brain tissue while facilitating precise microsurgical technique, as stated by the author.6

33.3 Operative Technique

33.3.1 Preoperative Preparation

The success of endoscopic approaches to intraparenchymal brain tumors depends mostly of the trajectory planned from the skin to the target area. For this, radiologic investigation is of significant importance. Volumetric acquisition in magnetic resonance imaging (MRI) and computed tomography (CT) scans are always done. Once images can be reconstructed in the three orthogonal planes, very accurate surface measurements can be taken to establish the entry point, along with a decision on use of frame or frameless stereotactic guidance. The entry point is determined by observing the trajectory needed to reach the target safely and with the best possibilities of total resection.

MRI tractography sometimes can help surgeons to elect a safer route, avoiding major white-matter fiber projections.11

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