LECTURE
Intraoperative Navigation and Fluorescence Imagings in
Malignant Glioma Surgery
Masahiro Toda

Department of Neurosurgery, Keio University School of Medicine, Tokyo, Japan(Received for publication on December 21, 2007)(Revised for publication on February 18, 2008)(Accepted for publication on March 27, 2008)

Abstract: The current basic goals in glioma surgery are radical tumor resection without
triggering the development of new neurological deficits. Although complete removal of malignant gliomas is extremely difficult because of the tumors’ infiltrative characteristics,
gross total resection of the tumor is known to be associated with improved outcome in thepatients. To enable safe and radical resection of malignant gliomas, especially those adjacent
to eloquent brain areas, rapid progress has been made in the development of operative support techniques; e.g., navigation systems to provide information about the anatomical andfunctional locations in the brain and a fluorescence imaging technique for differentiating
brain tumors from normal brain tissue. These intraoperative imaging techniques in glioma
surgery have improved the functional outcomes of glioma patients. (Keio J Med 57 (3) : 155－
161, September 2008)
Key words: glioma, imaging, navigation, fluorescence, surgery

Introduction
Gliomas are the most common malignant brain tumors.
With the currently available treatment modalities for malignant gliomas, the median survival still remains lessthan 2 years.1 Gliomas are characterized by an infiltrative nature, and extensive invasion into the surrounding
normal brain tissue is frequently seen. Even though themargin between the lesion and the normal brain is clearlydelineated on magnetic resonance images (MRI), it ishistologically obscure in most malignant glioma cases.
A basic goal of current glioma surgery is maximum tumor resection without triggering the development of newneurological symptoms. Although complete removal ofmalignant gliomas is extremely difficult, reduction of thetumor volume nonetheless decreases the compression of
the surrounding normal brain tissue and increases thetherapeutic efficacy of adjuvant therapies, including radiotherapy and chemotherapy. A correlation has actually
been reported between the tumor resection rate and theprognosis in patients with malignant gliomas.2, 3
Accurate intraoperative determination of the locationof the tumor and of the eloquent areas in the brain may

improve the rate of tumor resection. With the remarkableadvances in diagnostic imaging techniques, including
computed tomography (CT) and MRI, computerized
navigation systems have been developed, that allow realtime information to be obtained about the positions in theoperative field.4 -7 Research on the mapping of brain
functions has also progressed, and it is now possible toobtain information about locations associated with important functions (movement, speech, etc.). 8- 1 6 Although still in the clinical research stage, there have also
been some attempts to differentiate infiltrative tumors
from the normal brain tissue using fluorescent dyes andexcitation lights.17-22 This article provides an outline of
the navigation systems that provide information about
the anatomical and functional locations in the brain during surgery, and of a fluorescent imaging techniquewhich biologically identifies malignant brain tumors,with reference to our experience.
Intraoperative Navigation in Image-guided
Brain Tumor Surgery
In brain tumor surgery, accurate orientation is required

Corresponding Author: Masahiro Toda, M.D. Department of Neurosurgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo
160-8582, Japan, Phone: 81-3-5363-3587, Fax: 81-3-5363-3862, E-mail:todam@sc.itc.keio.ac.jp
155

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for tumor removal without interfering with important
brain structures. The surgical navigation system is an imaging support system which provides information about
positions in the actual operative field by coordinate representation, and the positions are confirmed intraoperatively by their reflection on the images.4, 5, 7 With thissystem, data, including preoperative CT or MRI findings,
are reconstructed on multiplanar 2-D images, i.e. axial,
coronal and sagittal slices, and the sites indicated with apointer probe are displayed in real-time on the images.
Using this system, surgery can be performed while ascertaining the 3-D orientation of the operative field, whichallows more accurate and safer surgical maneuvers.
Navigation systems
There are several types of navigation systems in termsof the detection method: e.g., the machine arm type, inwhich the distance between the probe tip and the starting
point of the arm and the angle are calculated and displayed, the magnetic field type, in which a magnetic fielddevelops in the operative field, based on which the position of the probe tip can be detected, and an optical type,which is equipped with an infrared camera. The optical
type of navigation system is currently the most widely
employed, because of its high accuracy and relatively
easy operability. We are currently using the StealthStation (Medtronic Sofamor Danek, Co., Ltd.), which is an
optical type of navigation system.23
The StealthStation consists of a Workstation with amonitor which displays the navigation images and an infrared camera which detects the position of the tip of apointer probe (Figure 1). The equipment includes a reference frame as an optical reference point for navigation
and a pointer probe for confirmation of the position.
Both have built-in light-emitting diodes (LED), including the active type, with a cord, which emits light, andthe passive type, without a cord, which is equipped witha reflective ball and utilizes reflected light from an infrared lamp source. The device also includes an adapter, the“Sure Trak System”, which allows surgical equipment to
be used instead of the pointer probe. The system allows
recognition of positional relations of the built-in LED or
the reflective ball attached to the tip of the equipment
and implementation of navigation. The adapter system is
especially useful for transnasal surgery in deep narrow
operative fields and for endoscopic surgery through a
one bar-hole in the ventricles in the brain.
The position is measured with an infrared camera according to the principle of triangular measurement, andinformation about the position of the pointer probe tip isdisplayed in real time on the images, obtained preoperatively (Figure 1). The advantage of the optical type ofnavigation system is that the accuracy of navigation is
maintained, independently of the surgical position or

Toda M: Intraoperative imagings in glioma surgery

movement of the infrared camera, because the reference
frame is integrated with the patient.
Application of the navigation system to brain tumor surgery
Markers for registration are applied to scalp sites, andthe necessary MRI and/or CT imaging are conducted before the operation. Routine axial images are obtained,
and the image information is loaded onto the StealthStation in the DICOM III format. Basically, the reference
frame is connected to the head frame for registration after the surgical position has been confirmed in the operating room. Another system for direct immobilization of
the reference frame to the head is also being developed
for cases in which head frame is not used, such as in thecase of transnasal surgery. The data for registration are
input by applying the pointer probe tip to the scalp.
There are 2 methods for registration in the StealthStation: point registration, in which the actual head is adjusted to the image data set up by using the markers on
the scalp before imaging, and surface registration, in
which the data collected at 40 or more points on the scalp
surface are randomly input to obtain the 3-D form. Stableregistration with high accuracy can be maintained using
these two registration methods.
When the pointer probe is applied to the operative
field, the probe tip position is displayed in real time on
the monitor, allowing confirmation of the orientation.
The display monitor can indicate multiplanar images ofaxial, coronal and sagittal slices. Virtual extension of the
tip on the software gives feedback on the position of any
point on the prolonged line of the probe. Therefore, it ispossible, as a matter of course, to let the virtual extensionof the tip invade the skull even before craniotomy. Thismethod provides for precise designing of the minimum
skin incision and craniotomy even prior to the brain tumor surgery.
The navigation system is mainly used to confirm, intraoperatively, the location of tumors and of importantfunctional areas, such as the motor and language areas,in the brain. Recently, identification of the eloquent areas
has become possible with the development of non-invasive techniques to analyze brain functions, such as functional MRI and magnetoencephalography (MEG).8, 1 0, 1 4
Utilization of these functional examinations allow important brain areas to be located even prior to the surgery.
By means of the navigator, tumors and eloquent areas
mapped on MRI images are accurately projected onto thebrain surface during the operation.
Thus, more accurate surgery has become possible withthe use of navigation systems. Actually, it has been reported that intraoperative neuronavigation in glioma surgery improves functional outcomes of glioma patients.24, 25 However, there are still problems that remain
to be resolved. The biggest of these is that navigation

Keio J Med 2008; 57 (3): 155－161

157

Fig. 1 Optical navigation system in brain tumor surgery. The infrared camera detects points of a pointer probe and a reference
frame as an optical reference point for navigation. The position of the pointer probe tip is displayed in real-time on images obtained
preoperatively.

surgery can only minimally deal with ‘brain shift’. Whenthe arachnoid membrane is incised during the operation,
cerebrospinal fluid flows out, causing brain deformity.
Some patients with severe brain edema may have marked
brain shift at the time of incision of the dura mater. As amatter of course, compression of the brain during a surgical procedure also causes considerable displacement.
Thus, navigation surgery using preoperative imaging
findings as reference cannot deal adequately with suchconsiderable brain shifts. To overcome this problem related to brain shift, we confirm the position of the tumors
and important areas by navigation as early as possible after craniotomy, and insert tubes at the margin of the tumor using the navigation system (Figure 2). Then, tumor
removal is performed using the anchored tubes as indicators.

As a countermeasure against brain shift, there have also
been some attempts to incorporate intraoperative ultrasonography into navigation and to display preoperative images of the same cross-sectional surfaces. By means of aposition detector attached to the ultrasonic probe, it may
become possible to confirm the degree and range of tumor removal with an echographic system and to compare
the findings with preoperative images. Re-examination
by MRI intraoperatively may also allow the problem
posed by such brain shifts to be overcome. Techniquesfor MRI in the operating room are being actively developed,26-28 and real-time imaging of lesions, which allowchanges along with the surgical maneuvers to be imaged,
have become possible. Fusion with such intraoperative
image updating techniques would allow more accurate
navigation to be conducted.29, 30

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Toda M: Intraoperative imagings in glioma surgery

Fluorescent dyes

Fig. 2 Image-guided glioma surgery using landmark-tubes.
As a countermeasure against brain shift during operation,
landmark-tubes are inserted at the margin of tumor by navigation
before tumor removal.

Intraoperative Fluorescence-guided
Surgery of Brain Tumors
The boundary between malignant gliomas, which are
infiltrative tumors, and the surrounding brain tissue ispoorly defined, and it is difficult to determine tumor
margins during operation. Until now, evaluation of tumor margins has been largely dependent on the surgeon’s
experience. In an attempt to delineate the margin between normal brain and tumor, a technique called intraoperative photodynamic diagnosis (PDD) has been developed.1 7, 2 0, 2 1, 3 1, 3 2 In this method, a fluorescent substance is incorporated into brain tumor, and the fluorescence detected during the operation allows the normal
brain tissue to be differentiated from the tumor tissue.
A basic principle underlying this method is that a fluorescent dye administered into the body leaks out of thetumor blood vessels due to the disrupted blood-brain barrier (BBB), which, when excited with an appropriate
wavelength of light, emits fluorescence which can be observed in the operative field through a filter. However,this technique has a disadvantage that the dye may leakout and emit fluorescence in the absence of the BBB
even at non-tumor sites. Recently, 5-aminolevulinic acid
(5-ALA), a precursor of heme, has been applied for PDD
in glioma patients;1 8, 2 0, 2 1, 3 2 5-ALA, which induces thesynthesis of protoporphyrin IX (Pp IX) in the mitochondria, has been shown to be incorporated into tumor cells
when administered orally. When the substance is irradiated with a violet-blue excitation light, the tumor cells
emit red fluorescence that can be observed through a filter.

1) Fluorescein sodium
Fluorescein sodium has been used in the field of
ophthalmology, mainly for fundus fluorescein angiography. It also has a long history of use in the field of
neurosurgery; even as early as in 1948, Moore et al.
had applied it to glioma surgery.33 Malignant gliomas
show marked hypervascularity at the margin of the tumor, which has a high density of tumor cells. Since
these blood vessels are deficient in normal BBB, fluorescein sodium (molecular weight, 332) easily passes
through the blood vessels. The blood vessels at thecenter of the tumor also differ from normal blood vessels, and do not have a BBB. Under these circumstances, the use of fluorescein sodium is appropriate for
PDD in glioma surgery; since fluorescence has beenrecognized to be consistent with the area of enhancement on CT or MRI images, removal of the part emitting fluorescence allows removal of the tumor itself.34
2) 5-Aminolevulinic acid (5-ALA)
5-ALA is a natural biochemical precursor of hemethat induces the synthesis of the fluorescent molecule,
Pp IX, through metabolic conversion in the mitochondria.35 5-ALA (molecular weight, 167.6) given via theoral route normally does not enter the normal brain tissue, because of the presence of the BBB. However, it
can easily pass through the disrupted BBB in the glioma tissue.2 1 Since Pp IX emits peak fluorescence at
635 nm with a peak excitation wavelength at 405 nm,
it is observed as a red light through a filter that allows
this wavelength to pass. Clinical use of 5-ALA for
photodynamic therapy (PDT) or PDD has also been reported for lung cancer, ovarian cancer, and bladdercancer.36-38 In the USA, it has been used with the approval of the Food and Drug Administration (FDA) asa therapeutic drug for solar keratosis, while its use has
not yet been approved by the pharmaceutical authority
in Japan, and it is only used after obtaining approval of
the ethics committee of the respective institutes. The
tumor tissue concentration of the fluorescent dye peaks
at 2-6 hours after oral administration, and disappearsby 12 hours. Administration of antacid should be
avoided at the time of oral administration of the dye,because the dye is easily decomposed in the presenceof alkali.
Use of 5-ALA is contraindicated in cases of porphyria, a genetic disease. Pp IX biosynthesized from 5-ALA
is a phototoxic substance, although the incidence ofskin photosensitivity is lower than that reported forconventional porphyrin derivatives. 2 0 Since the administered 5-ALA is excreted into the urine within 24
hours after oral administration and does not remain in
the skin, the occurrence of photosensitivity can be ade-

Keio J Med 2008; 57 (3): 155－161

159

����

Fig. 3 Fluorescence-guided glioma surgery using 5-ALA
Red fluorescence emitted by protoporphyrin IX, that is biosynthesized from 5-ALA, in tumor tissue is observed with a violet-bluelaser light.

quately prevented by avoiding sun exposure for approximately 24 hours after the administration.
Application of 5-ALA in fluorescence-guided glioma surgery
Before induction of general anesthesia, 20 mg/kg of
5-ALA (Cosmo Oil Co., Ltd.) is dissolved in 50 ml of
5% glucose and administered orally. After the inductionof general anesthesia, routine craniotomy is conducted.
We use a semiconductor laser system (VLDM1, M & M
Co., Ltd.) as the excitation light source. During the tumor
resection, red fluorescence emitted from the Pp IX in thetumor tissue is observed with a 405-nm violet-blue lightemitted from a laser system (Figure 3), which allows
normal brain tissue to be differentiated from the tumor
tissue.
Intraoperative identification of the margin between a glioma and normal brain tissue is the objective of PDD using
5-ALA. A rondomised cotrolled clinical phase III trial
showed that fluorescence-guided surgery with 5-ALA improved progression-free survival in glioma patients.2 0
However, the fluorescein may occasionally be weak andautologous fluorescence in the background may also influence the identification. Therefore, more objective andquantitative indicators need to be established. Recently, aquantitative determination method for fluorescence involving spectroscopic analysis has been developed,

which allows more precise visualization of the fluorescence from tumor tissue.22 Regarding the specificity of
PDD for glioma surgery, new techniques allowing more
specific accumulation of fluorescent dyes in tumors need
to be developed. We have found several glioma antigens
that are strongly expressed in glioma tissues, but not in
the normal brain.39-43 Fluorescent dyes labeled with antibodies against glioma antigens may be useful to increase
the specificity of PDD in glioma surgery.
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