**5. Conclusion**

of the tumour, which requires the dissection and coagulation of the vascular afferences from

During the resection of ISCT, lesions in neural structures can inadvertently occur, potential‐ ly creating severe neurological deficits. IONM of the spinal cord plays an important role in

As previously described, an effective strategy could be to adapt IONM to the steps of the surgery to protect the somato-sensory and motor pathways [70]. Therefore, monitoring with

Additionally, for spinal cord surgery, D wave recording is widely used and recommended. In well-documented studies of more than 100 ISCT surgeries, a preserved D wave up to 50% of the original amplitude, with a complete loss of muscle MEPs, has been shown to result in only

Although it also has disadvantages, we generally consider that under those circumstances in which the mechanism of injury to the spinal cord is purely ischemic, D wave monitoring does not add a significantly value to muscle MEP monitoring. Grey matter is more sensitive than white matter to cord ischemia, and both clinical and experimental data suggest that both peripheral and myogenic MEP disappear earlier than the D wave when spinal cord vascular‐ isation is acutely compromised [72]. Regarding this issue, it seems logical to postulate that the nerve structures most likely to be affected during an ischemic alteration in ISCT surgery are

It is important to note that previous observations of EMG may improve the reliability of IONM during spinal cord surgery [73, 74]. Skinner and Transfeldt [75] have reported experience with EMG for monitoring ISCT in 14 patients. They described segmental and suprasegmental elicitation of neurotonic discharges that could anticipate the loss of MEP and predict a postoperative motor deficit. Moreover, some studies have associated spinal cord mechanical and thermal injury with EMG activity and motor conduction block (MEP loss) in animals [75,

In our experience, we can define three different phases of the surgical approach to ISCTs that must be followed by the neurophysiological techniques used (**Figure 5**).(i) Phase A: during posterior median sulcus opening, it is important to protect the dorsal columns by monitor‐ ing the somato-sensory evoked potentials (SSEPs). (ii) Phase B: working at the cleavage plane, monitoring of motor evoked potentials (MEPs) is mandatory, mainly to protect the cortico‐ spinal tract in the lateral cords during the separation between the sidewall of the tumour and the spinal cord tissue. (iii) Phase C: the final phase of complete tumour removal during which, as previously mentioned, the anterior vascular supply is threatened and consequently there is

a certain risk of injuring the AH. Thus, fEMG is critical during this phase.

the anterior spinal artery.

232 Neurooncology - Newer Developments

*4.5.2. Particularities of IONM*

SSEP and MEP is indicated.

transient paraplegia [71].

the anterior horns (AH).

76].

facilitating the resection of these tumours [69].

IONMis a cheapandeffective methodforreducing the risk ofpermanentpostoperativedeficits in many different operations in which NS is undergoing manipulation. It provides real-time monitoring of function to an extent that makes it superior to imaging methods that provide information about structures but not about the physiological state of the patient.

Intraoperative neurophysiology must be conducted by teams of experts that include a clinical neurophysiologist with a thorough understanding of neuroscience and the pathophysiology of the disorders that are to be treated.

Therefore, we can conclude without exaggerating that IONM and mapping are some of the techniques with more relevance during recent decades for oncological neurosurgery. The widespread use and improvement of these techniques have allowed better functional postsurgical outcomes, increasing life expectancy together with better functionality.

However, different topics have been debated that must be clarified. Among these are param‐ eters for stimulation, indications regarding awake versus anaesthetized craniotomy, differ‐ ent types of DCS, and a better definition of the warning criteria or the prognostic utility of some surgeries. Future investigations will clarify most of these features and will undoubted‐ ly contribute to improve outcomes in neuro-oncology.
