*2.1.1.3. Navigation-guided glioma biopsy*

*2.1.1. Glioma biopsy*

152 Glioma - Contemporary Diagnostic and Therapeutic Approaches

*2.1.1.1. Frame-based stereotaxis*

that connects the corners.

supervision (CT or MRI).

*2.1.1.2. Frameless stereotaxis*

Glioma biopsy is the standard procedure for taking tissue samples of tumors with a minimally invasive approach. It consists of taking a sample of tissue through a minimum opening of the skull. Biopsy indications are tumors in difficultly accessible brain zones, multicenter lesions, and pathology where it is advisable to establish a pathohistological diagnosis, which will then determine further surgical or nonsurgical treatment (e.g., whether it is tumor glioma or lymphoma; the former will then undergo resection, while the latter is mainly nonsurgically treated). On the other hand, very advanced gliomas and gliomas in the elderly who are not candidates for a more aggressive approach (open surgery) are also indications for biopsy. Minimally invasive approaches have been favored for a long time in neurosurgery for glioma resection.

Today, Leksell G frame is still the most widely used, consisting of two parts—one fixed quadrangular and the other moving, the so-called arc. The fixed part consists of four graduated rods. On the right or left side of the patient, there is a diagonal bar in the form of the letter "N"

Of the four basic geometric systems used in frame-based navigation systems, the "arc radius" system is the most commonly used, which is the base of the Leksell frame. The principle of the C arc is based on the ability to reach the center of the C arc from all directions by moving the probe along the radius of the frame. The frame itself is fixed on the patient's head, while the C arc is a movable part with the possibility of penetrating with a puncturing needle through any point on the convexity of the skull. The advantages of the Leksell frame design are the ability to reach any intracranial point with great precision and the ability to use it directly under the control of CT or MRI. One of the disadvantages is the bulkiness of the device itself, the obstruction of the operating field, and the "non-real time" procedure if there is no radiological

By setting up the frame and the effect of the CT scanning, the center is first marked in anterior–posterior direction. The center is observed on axial CT scans in the form of the letter X by joining the frame corners. On the vertical plane, the center is marked by pulling the corner line through the mid-point of the letter "N." After defining the center, the target point is defined in relation to the geometric center of the frame and it can be accurately calculated, after which

Next evolutionary step in the development of stereotaxis was frameless stereotaxis. Framebased stereotaxis is a clearly defined relationship between two coordinate systems (preoperative and intraoperative) and a precise position in relation to the planned procedure without further need for determining coordinates. Frameless stereotaxis, unlike frame-based, uses "point pair" registration to establish a relationship between preoperative images and surgical

the C arc is moved and the probe is placed in the center of the lesion.

Most important indications for neuronavigation in glioma surgery are:

	- early diagnosis with minimal risk
	- deep lesions (thalamic gliomas, basal ganglia etc.)
	- patients with a high operative risk in case of prolonged anesthesia or those with advanced diseases and poor prognosis compared to co-morbidity
	- multiple lesions
	- patients who reject the proposed surgery for resection
	- patients with "unsafe" radiological diagnosis and suspicion of infectious or demyelinating disease
	- cyst drainage
	- intratumoral chemotherapy
	- intratumoral radiotherapy

Unrelated to the use of neuronavigation in oncology or the treatment of gliomas, neuronavigation can be used in ventriculostomy, electrode placement for deep brain stimulation, endoscopic neurosurgery, etc.
