**3.1. Functional mapping**

*2.3.5. Stimulated electromyography (sEMG)*

misleading information.

220 Neurooncology - Newer Developments

For this technique, EMG is induced by an electrical shock that is delivered consciously, in contrast to the application described for fEMG. The pulses are usually delivered through bipolar (either concentric or parallel) or monopolar probes. In the latter case, it is important to use a cathodal current to stimulate the nerve and place the anode at a non-stimulated tissue.

The parameters must include pulses of a short length to avoid diffusion of the current. Normally, 50–100 μs should be adequate. The current must be maintained as low as possible to avoid injury to the neural tissue and diffusion. The latter effect must be considered in particular when a functional block is apparent because a high current or a long pulse (or both) can stimulate a region of the nerve distal in the damaged or blocked area and result in

It is common to use sEMG in the next situation: (i) to explore a region to identify the proxim‐ ity of nerves that are not easily visible (e.g., when the CN runs inside a schwannoma); (ii) to determine the identity of a nerve; (iii) to evaluate the functionality of the nerve. We usually measure the threshold to elicit a muscularresponse at two different points (proximal and distal to the region at risk or more damaged by the surgery) and calculate the ratio of *i*distal/*i*proximal.

The settings used to record sEMG depend on the muscle being recorded, but it is quite common to use a 50–3000 Hz bandwidth, with the notch off, a gain consistently greater than 30 μV/div

In recent years, there has been a renewed interest in surgery in awake patients [38,40,41]. This procedure uses the asleep–awake–sleep anaesthetic technique, which consists of induction with propofol + sevoflurane and topical blocking with svedocain + lidocaine around the skin incision. During exploration, the patient must be awaken slowly by removing the sedation. In recent years, a new anaesthetic, dexmedetomidine, has been introduced forthis type of surgery

Cortical stimulation is usually performed through a bipolar probe with ball-tips that are separated by 0.5 cm. It is common to use 60 Hz trains over 1–4 s. The pulse width is usually 1

A low rate of intraoperative seizures has been reported (approximately 3–3.4%) [44], and some authors have concluded that control by ECoG is not mandatory [42]. However, this conclu‐

In addition to this prevention, some authors have focussed on possible secondary effects derived from this technique. A normal human response to such an exceptional situation as awake craniotomy can, for instance, result in the delayed appearance of unintentional distressing recollections of the event or some type of post-traumatic stress disorder (as yet

undescribed), despite the satisfaction of the patient concerning the procedure [45].

The closer this ratio is to 1, the better the function of the nerve.

(typically 50 μV/div), and a time base between 1.5 and 4.5 ms/div.

**2.4. Cortical and subcortical surgery in awake patients**

and is considered the most effective [18].

ms, with a current intensity of 2.5–10 mA [42,43].

sion has been debated and remains to be validated.

Functional mapping generally consists of the topographic assessment (although sometimes it is merely qualitative) of various structures to determine the functions that lead to or sit on the structures [9].

From the perspective of duration, it is usually short so that mapping ceases as soon as the function is positively identified. The objectives, as mentioned previously, are purely descrip‐ tive.

The changes during surgery are usually minor, especially because the surgery has a limited duration.

A typical example of mapping is the identification of eloquent areas in cortical surgery. In this case, the issue is to identify the eloquentregions. Thus, the surgeon knows the function of each region so he/she can decide where to position the incision or how far it can be moved prior to the detection of eloquent structures.
