Acta Neurochir (Wien) (2005) 147: 811–813

DOI 10.1007/s00701-005-0565-8

EditorialWhat the surgeon wins, and what the surgeon loses from intraoperativeneurophysiologic monitoring?

G. Neuloh and J. Schramm

Department of Neurosurgery, University of Bonn, Bonn, Germany

Published online June 30, 2005

# Springer-Verlag 2005

When the operating microscope was introduced into

neurosurgical practice in the 1970s, many experienced

and highly accomplished neurosurgeons would not read-

ily adopt this technical innovation. They felt they could

obtain excellent results without the new method. Large

series of, e.g., cerebral aneurysm cases were published

which had been successfully treated without microsur-

gical techniques. It took more than one generation of

neurosurgeons growing up with the new technology to

establish microsurgery as the indispensable standard in

many areas of contemporary neurosurgery.

There is some analogy between this situation and the

introduction of intraoperative neurophysiologic mapping

and monitoring methods for a functionally guided ap-

proach in neurosurgery. Pioneer neurosurgeons such as

H. Cushing, O. Foerster, and W. Penfield used electrical

cortex stimulation since the very beginnings of modern

brain surgery, both for scientific and clinical purposes.

The current revival of awake brain tumor surgery

implies a broad adoption of Penfield’s brain stimulation

method and implies acceptance for the necessity of func-

tional guidance in certain cases. Likewise, only valida-

tion by neurophysiologic means will allow the useful

application of recent functional imaging methods for

surgery planning. Complex brainstem surgery is hardly

done without cranial nerve EMG mapping and moni-

toring. Microrecordings guide the implantation of elec-

trodes for deep brain stimulation. The continuous

recording of evoked potentials allows to monitor audi-

tory, somatosensory, and in particular motor pathways in

the anesthetized patient during tumor and vascular sur-

gery in the spinal cord and the brain.

However, neurophysiological methods are not yet

generally perceived to be an indispensable adjunct in

modern neurosurgery. For many accomplished surgeons,

the additional neurophysiologic information does not

justify the additional expense in time and money. They

feel they are obtaining good results without those func-

tional data. Frequently they argue that there is not suffi-

cient truly scientific evidence to make them adopt this

technology. They raise general objections against the

idea of a functionally guided approach: ‘‘What will

you do if your recordings deteriorate, will you leave

the tumor in?’’ they frequently ask. There is a grain of

truth in all those concerns. As a matter of fact, the evi-

dence which is currently available does not oblige every

neurosurgeon to rely on intraoperative neurophysiologic

methods. Nevertheless, there are recent data clearly sup-

porting the claim that most neurosurgeons will benefit in

some way from the application of intraoperative neuro-

physiologic methods.

The case is rather clear with an inexperienced surgeon

who is still on the ascending branch of his or her perso-

nal learning curve. Any immediate feedback about the

consequences of what he is doing should be highly wel-

come to him because this will steepen the learning

curve. Moreover, the reassurance that a certain maneu-

ver, e.g., manipulating a vessel or retracting a certain

brain area, can be safely done may be very helpful to

the inexperienced surgeon who would otherwise sidestep

to a less optimal solution – and would always remain in

doubt about the true value and risks of his original inten-

tion. There is considerable evidence that neurophysiolo-

gic monitoring can serve these purposes at the current

stage. For example, it has been shown in prospective

studies that intraoperatively recorded motor evoked

potentials reliably correlate with the postoperative motor

outcome in cerebral aneurysm surgery. Whereas unim-

paired MEPs indicate the preserved functional integrity

of motor pathways, lost MEPs predict a lasting new

motor deficit, e.g. from ischaemia to motor pathways.

The surgeon can reconstruct at which point of time, and

by which maneuver during the procedure he had induced

the new deficit, e.g., by inadequate brain retraction with

kinking of perforating vessels. With growing experience

he will then be better able to assess the risks of specific

maneuvers, even without neurophysiologic measure-

ments. This means that there is no reason to fear an

inadequate dependence of the surgeon on these methods.

However, surgeons who are familiar by training with the

neurophysiologic techniques will be able to take advan-

tage of them later on, and experience has shown that

they will continue to do critical cases with functional

data available if possible.

The more experienced neurosurgeon, who has a full

repertoire of operation skills will nevertheless frequently

benefit from intraoperative neurophysiologic monitor-

ing. He can use monitoring methods to adjust and

improve a general surgical technique. For example,

acoustic neuroma surgeons have learned from monitor-

ing observations no longer to electrocoagulate vessels of

the tumor capsule in order to avoid heat lesions of the

cranial nerves. Moreover, there are many procedures,

e.g., in eloquent brain areas, which are safely planned

and performed under neurophysiologic mapping and

monitoring, but cannot be considered without this func-

tional guidance. Although the more experienced surgeon

will know the possible sequelae of a particular standard

maneuver, there are situations where such a general

knowledge may not be sufficient. For example the radi-

cal resection of a deeply seated, infiltrative tumor adja-

cent to motor pathways, can only be achieved when

recording of functional data allows to determine the

point where to abandon resection before irreversible

motor deficit will occur. There is clear evidence avail-

able now from prospectively collected data in the litera-

ture that deterioration of the evoked potentials, or a

response to subcortical stimulation will indicate impend-

ing damage early enough to allow the surgeon to equal-

ize the interfering factor, e.g., by abandoning or pausing

resection. However, this example highlights at the same

time the drawbacks of an undifferentiated, na€��ve utiliza-

tion of neurophysiologic criteria for intraoperative deci-

sion making. An overcautious surgeon will tend to

abandon the tumor resection prematurely with some gra-

dual deterioration of the evoked potentials, and will thus

obtain an unsatisfying extent of cytoreduction. Contra-

rily, stable recordings may seduce the more incautious

type of surgeon to proceed hastily, and to take unneces-

sary risks. Therefore, the functional data always have to

be assessed in the context of the given anatomical situs,

the preceding course of the operation, and possibly other

adjunctive information such as imaging and navigational

data. The surgeon must still base his decision on a coher-

ent overall picture of all available data rather than one

single measurement result. It is certainly not a promise

of the intraoperative neurophysiologic methods ever to

provide such a universal criterion, although unrealistic

expectancies of this kind are frequently put forward in

order to challenge the method. However, the relative

importance of neurophysiologic monitoring data as

related to other intraoperative observations will be deter-

mined by their impact on clinical outcome in future

controlled studies. If such studies confirm the positive

results of those retrospective evaluations which have

already been conducted, e.g. showing a clearly reduced

deficit rate in neurovascular decompression procedures

conducted under BAEP and facial nerve monitoring, the

general adoption of the method in many areas of neuro-

surgery will inevitably occur.

At present, objections against the general use of

intraoperative neurophysiological data are frequently

expressed by highly experienced specialists and opinion

leaders who have always been working without this aid,

and have nevertheless achieved good results, e.g., in

cerebral aneurysm surgery. Those experts may perceive

the new functional information as an obstruction rather

than a facilitation of their work. From their large experi-

ence they are able to assess the impact of an intra-

operative maneuver on the clinical outcome without

complementary data. However, they must not forget that

the majority of surgeons in their field does not have the

same level of expertise and will benefit from some addi-

tional functional feedback information. Moreover, their

objections will lose more and more momentum with the

continuously growing stock of good quality data about

the benefits of neurophysiologic monitoring, and with

the growing number of surgeons adopting these meth-

ods. It must also be reminded that renowned experts in a

number of advanced neurosurgical procedures, such as

812 G. Neuloh and J. Schramm

the surgery of intrinsic tumors of the brainstem and the

insula, belong to the strongest proponents of neurophy-

siologic monitoring.

In summary, we can observe that – at the present

standard of knowledge – the majority of neurosurgeons

will benefit from the functional guidance by intraopera-

tive neurophysiologic methods. The surgeon who in-

appropriately regards those methods as a universal

criterion for his decisions and disregards other intra-

operative observations will not obtain the desired results,

though. Accomplished experts in some fields of neuro-

surgery may still be skeptical about the true value of

neurophysiologic monitoring, based on their personal

positive experience without such techniques. With the

currently growing adoption of the neurophysiologic

methods the number of skeptics will get smaller in the

future. Nevertheless it remains a challenge to the propo-

nents of these methods to provide controlled prospective

data which can eventually prove the positive effect of

neurophysiologic monitoring on the clinical outcome of

neurosurgery.

Correspondence: Johannes Schramm, Universitatsklinikum Bonn,

Sigmund-Freud-Strasbe 25, 53105 Bonn, Germany. e-mail: Johannes.

Schramm@ukb.uni-bonn.de

What the surgeon wins, and what the surgeon loses? 813