FOCUS SESSION
Intraoperative neurophysiology is here to stay
Francesco Sala
Received: 24 January 2010 /Accepted: 25 January 2010 /Published online: 24 February 2010
# Springer-Verlag 2010
Preface
The 2010 February and April issues of Child’s Nervous
System offer to the readers two very timely focus sessions in
the field of “neuromonitoring”. This was the topic of a
symposium held in Cape Town in October 2008—as a
satellite event of the 36th Meeting of the International
Society for Pediatric Neurosurgery—aimed to cover the
various techniques available to neurosurgeons for keeping
under control the brain and the spinal cord, both in the
operating room and the intensive care unit. What
emerged from that symposium is presented in these
focus sessions, where international experts in traumatic
brain injury (see the Editorial of Dr. Figaji in the February
issue of Child’s Nervous System) and intraoperative neuro-
physiology address the aspects of these disciplines relevant
to pediatric neurosurgery.
Introduction
Intraoperative neurophysiology (IN) has emerged over the
last decade, as one of the main avenues of progress within
neurosurgery. The idea of applying techniques traditionally
used in clinical neurophysiology within the neurosurgical
operating room is not novel. Somatosensory (SEPs) and
brainstem auditory evoked potentials (BAEPs) have been
used for many years during neurosurgical procedures [5, 7].
Direct mapping of the exposed cortex to localize motor and
language areas dates back to the end of the nineteenth
century [4]. In the recent past, there has been a renewed drive
toward the implementation of these techniques, thanks to the
advent of new methods, such as motor evoked potentials
(MEPs). Recording MEPs under general anesthesia [24] has
allowed for an increase in the indications for IN and has
also expanded clinical research in brain and especially in
spinal cord surgery.
Intraoperative neurophysiology is aimed at either identi-
fying functional structures which cannot be recognized
purely on the basis of anatomical landmarks (mapping) or
to continuously assess the functional integrity of neural
pathways which can be injured during surgery (monitoring).
The “Why, When and How” regarding the use of IN in
pediatric neurosurgery has been the topic of a review which
appeared in Child’s Nervous System in 2002 [22]. The
rationale and indications for IN have not substantially
changed since then. Methodologies have to some extent
evolved, although the basic principles of monitoring and
mapping techniques remain the same. Nevertheless, IN has
undoubtedly become more and more accessible and
extensively used than it has been in the past. The growing
interest for this discipline is well documented by the
increasing number of publications in this field, both in the
form of peer-reviewed papers and edited books as well as
by the number of scientific meetings dedicated to intra-
operative neurophysiologic monitoring.
There are scientific societies, such as the American
Society for Neurophysiological Monitoring and the Inter-
national Society for Intraoperative Neurophysiology, whose
members are dedicated full- or part-time to IN in their daily
practice. These and other scientific societies are now facing
the need to establish guidelines, credentials, and training
requirements for the practice of IN [16]. The spectrum of
expertise and advancements in this field varies quite
F. Sala (*)
Section of Neurosurgery, Department of Neurological
and Visual Sciences, University Hospital,
Piazzale Stefani 1,
37124 Verona, Italy
e-mail: francesco.sala@univr.it
Childs Nerv Syst (2010) 26:413–417
DOI 10.1007/s00381-010-1090-5

considerably across different countries, but there is no
doubt that the driving force is not limited to Europe, North
America, and Japan and involves, to a different extent,
virtually all five continents.
Intraoperative neurophysiology and the neurosurgeon
Intraoperative neurophysiology is favored by many neuro-
surgeons nowadays, but this has not always been the case.
In 1994, Dr. Leonard Malis, a master of modern neurosur-
gery, wrote that: “Monitoring has the same place as training
wheels on a bicycle; they are of considerable use for the
learning youngster, yet perhaps are a detriment to the
skilled cyclist because of increase in time expended and in
cost” [14]. At that time, MEP monitoring was in its infancy
and most of IN was based on SEPs and BAEP. False-
negative results—namely a patient waking up from anes-
thesia with a motor deficit in spite of intraoperatively
preserved SEPs—could occur, and this detracted from the
reliability of IN [9, 12]. Moreover, neuromonitoring was
erroneously considered useful merely for predicting the
outcome but not for preventing neurological deficits and this
also contributed to its lack of popularity among neuro-
surgeons. The feeling of “wasting time”when performing IN
techniques is still a concern for a number of neurosurgeons,
as well as the idea that IN sometimes unjustifiably hinders
rather than facilitates the removal of a tumor.
In analogy to the introduction of the operating micro-
scope in the 1970s—far from being widely accepted at that
time—IN had to find its way to become welcome in the
operating room. The idea of a different professional figure
(namely a neurologist or clinical neurophysiologist) work-
ing hand in hand with the neurosurgeon in the operating
room and advising him whether or not his surgical strategy
was impairing the well-being of the nervous system was
(and still is) something not readily acceptable to neuro-
surgeons. The classical reply to the neurophysiologist when
a warning message was passed to the neurosurgeon often
sounded like: “I didn’t do anything, maybe you should
check your electrodes first...” Neurophysiological feedback
was generally welcome as long as it reassured the
neurosurgeon that everything was going well (“Am I doing
OK? Are your evoked potentials stable?...”), but was not so
well-received whenever there was a change in the evoked
potentials that would imply the need to halt or even
abandon surgery. Transcranial electrical stimulation for
motor evoked potential monitoring sometimes induces
muscle twitches that can be bothersome when working
under magnification. This has also been a concern to some
neurosurgeons.
This reluctance to use IN has significantly changed in the
past decade, together with an increasing acknowledgement
of the reliability and value of IN in our practice. Good
neurological outcome in clinical series where IN has been
used and historical control studies where monitored patients
did better than those operated on without neurophysiologic
monitoring contribute in giving credit to IN.
Yet, some resistance to the use of IN still exists
nowadays and relies mainly on the criticism that the use
of IN is not “evidence-based”.
Is it evidence-based?
There is little discussion about the fact that IN is not based
on class I evidence. Yet, we may ask ourselves what level
of evidence we do need to justify the use of a certain
medical or surgical treatment. In this regard, two comments
are imperative.
First, there is a growing concern about the true level of
evidence in evidence-based medicine (EBM), and this is
due to the conflict of interest in biomedical research. About
75% of the clinical trials published in highly ranked
medical journals are industry funded, with two thirds of
these trials conducted by for-profit research companies
rather than academic medical centers [1]. It has therefore
been suggested that EBM sometimes has more to do with
institutional costs and profits than with the patient’s health.
Therefore, while recognizing that EBM is supposedly
motivated by the desire to provide the best and most
modern care available, we have to take EBM with a pinch
of salt and be cautious in uncritically grounding our clinical
practice on EBM studies alone [13].
Second, although the level of evidence for the benefit of
IN is limited to class II and class III studies, it should be
recognized that the same level of evidence applies to most of
our clinical practice within neurosurgery. From the surgical
treatment of acute spinal cord injuries [3, 25] to that of
aneurysms [19, 26], traumatic brain injury [21], and benign
brain tumors [2], even the more accredited analyses (such
as Cochrane reviews) fail to demonstrate class I evidence.
So, after all, we have to admit that the level of EBM in IN
is not worse than that found in neurosurgery generally.
It is very unlikely that class I studies will ever occur in the
field of IN. There are at least two reasons for this. First, the
likelihood of preventing a neurological deficit using IN is so
high for certain pathologies (for example spinal cord tumors)
that a controlled study where patients are randomly assigned
to a control group or a monitored group would be unethical
and unacceptable to patient and surgeon alike [6, 18].
Second, the incidence of severe and permanent neuro-
logical complications for standard pediatric neurosurgical
procedures is quite low. Thus, IN would aim at further
reducing a number that is already small to begin with. A
power calculation study would therefore predict that the
414 Childs Nerv Syst (2010) 26:413–417