Technology

Preoperative PET Activation for
Assessment of Motor Cortex Area
in Precentral Chondroma
Mathias Schreckenberger, M.D.,* Uwe Spetzger, M.D.,† Osama Sabri, M.D.,*
Philipp Meyer,* Gernot Schulz, M.D.,* Benita Hermanns, M.D.,#
Gabriele Krombach, M.D.,† Joachim Gilsbach, M.D.,† and Udalrich Buell, M.D.*
Departments of *Nuclear Medicine, †Neurosurgery, and #Neuropathology, Aachen
University of Technology, Aachen, Germany

Schreckenberger M, Spetzger U, Sabri O, Meyer P, Schulz G,
Hermanns B, Krombach G, Gilsbach J, Buell V. Preoperative PET
activation for assessment of motor cortex area in precentral
chondroma. Surg Neurol 1999;52:24 –9.
BACKGROUND

A main problem in the preoperative planning for precentral tumors is the exact assessment of the spatial relationship between the tumor and the functionally relevant
brain areas, which may be difficult using only morphologically oriented imaging (CT, MRI). Therefore, we applied
motor activation PET and PET/MRI overlay in a patient
with a precentral tumor.
DESCRIPTION

We report the case of a 21-year-old woman suffering from
progressive right-sided headache and intermittent dysesthesia of the left leg. MRI showed a hypointense tumor
with inhomogenous contrast enhancement in the right
precentral area. For preoperative assessment of the spatial relationship between the tumor and the motor cortex
area, the patient underwent two F-18-fluorodeoxyglucose
positron emission tomography (PET) scans (1. resting
condition and 2. motor activation of the left leg) and
subsequent calculation of subtraction images of activation minus rest. Fusion of PET and MRI data (PET/MRI
overlay) was performed for bimodal function and morphology presentation. PET revealed an activation pattern
behind and below the tumor, indicating that the motor
cortex area was shifted to the back. PET findings were
confirmed by intraoperative electrophysiology. Cortical
stimulation combined with intraoperative neuronavigation localized the motor area of the left foot and leg
exactly at the dorsal border, below and lateral to the
lesion. After complete resection of the solid tumor, histopathological examination revealed a chondroma. The
postoperative course was uneventful, and the patient was
discharged without neurological deficits.

Address reprint requests to: Dr. Mathias Schreckenberger, Department
of Nuclear Medicine, Aachen University of Technology, Pauwelsstrasse 30,
52057 Aachen, Germany.
Received September 16, 1997; accepted June 15, 1998.
0090-3019/99/$–see front matter
PII S0090-3019(99)00035-X

CONCLUSIONS

This case shows that biomodal imaging (PET/MRI) provides a noninvasive exact assessment of functionally important cortex areas for preoperative planning in patients
with cerebral lesions. © 1999 by Elsevier Science Inc.
KEY WORDS

PET, 18F-fluorodeoxyglucose, motor activation, PET/MRI
overlay, preoperative planning, chondroma, precentral
area.

ositron emission tomography (PET) enables
an assessment of the perfusional and metabolic cerebral processes which are correlated with
sensorimotor or cognitive tasks. Depending on the
applied radiotracer, regional cerebral perfusion
(H215O, 15O-butanol) or regional cerebral glucose
metabolism (18F-fluorodeoxyglucose) as markers
for neuronal activity can be detected with sufficient
spatial resolution (4 – 6 mm). For recording functionally important brain areas, PET studies using a
special activation paradigm (e.g., motor or sensory
task, language task) [16] reveal the activated brain
areas by calculating parametric subtraction images
activation minus rest. Image fusion of one patient’s
PET and MRI data (PET/MRI overlay) enables bimodal presentation of individual anatomy and function. Information about the exact spatial extent of
functionally relevant brain areas (e.g., primary motor cortex, Broca’s area) is important for the preoperative planning of the approach to avoid or minimize surgically induced cortex damage. Using only
morphologically oriented imaging (CT, MRI), this
assessment is very problematic due to the considerable interindividual variability of primary motor
cortex [3,17] and language related cortex [13,18],

P

© 1999 by Elsevier Science Inc.
655 Avenue of the Americas, New York, NY 10010

Preoperative PET activation in precentral chondroma

Surg Neurol
1999;52:24 –9

25

and to the displacement of these areas by slowly
growing tumors.

Case Report
A 21-year-old woman was admitted with progressive right-sided headache and intermittent dysesthesia of the left leg in the form of sensory Jacksonian seizures. Clinical examination showed normal
neurologic status without focal signs.
PREOPERATIVE IMAGING
CT scan demonstrated an isodense lesion (3 3 2 3
1.5 cm) without calcification and no contrast enhancement in the right precentral gyrus that was
attached to the falx cerebri and the sagittal sinus.
MRI revealed a hypointense central signal with inhomogenous and ring-shaped contrast enhancement on T1-weighted images after administration of
gadolinium. No peritumoral edema was seen on T2weighted sequences. The sagittal sinus was slightly
compressed, but not completely occluded (Figure
1).
For preoperative planning, the patient underwent
a T1-weighted 3D-flash MRI (Magnetom 1.5 T, Siemens, Erlangen, Germany) and two PET scans
(ECAT Exact, Siemens, Erlangen, Germany) on two
consecutive days. The first PET scan was performed 30 min. after i.v. injection of 315 MBq F-18fluorodeoxyglucose (18-FDG) under resting conditions (dimmed light, closed eyes, no sensorimotor
or cognitive activation). The second scan was performed on the following day under a specific motor
activation task: 1 min. before i.v. injection of 285
MBq 18-FDG, the patient was asked to start moving
the left lower leg and foot by regular stretching for
30 min. with subsequent PET scanning. After normalization of the global cerebral counts of the first
PET scan to the global cerebral counts of the second scan, MRI and PET data were realigned using a
special multi-purpose imaging tool [15]. Thereafter,
subtraction images activation minus rest were calculated and fused with the MRI data (PET/MRI
overlay).
PET images under resting conditions revealed a
lack of glucose metabolism in the area of the right
medial precentral gyrus that exceeded the tumor
region, indicating a reduced glucose metabolism in
the morphologically normal cortex around the tumor. Within the tumor area, the lack of evidence of
hypermetabolic tissue would point away from a
high-grade glioma. The subtraction images (Figure
2) demonstrating the cortex area activated by the
motor task, revealed an increased cerebral glucose

MRI showing a parafalxial lesion in the right sensorimotor cortex. (A) Axial T1 images (TR480/ TE 15)
demonstrate hypointense signal and (B) high intensity on
axial T2 images (TR 3500/ TE 100) without perifocal
edema. The central sulcus is clearly visible (arrow). Coronal (C) gadolinium enhanced T1 image (TR 420/ TE 20)
shows oval-shaped and inhomogenous ring-like contrast
enhancement.

1

metabolism in the area behind, lateral to, and below
the tumor. Additionally, considerable activation
was seen in the bilateral cerebellum. Remarkably,
no motor activation could be found in front of the
tumor area.
SURGERY
After preoperative planning and targeting of the
right parietal cortex, parasagittal craniotomy was
performed using the neuronavigation system
EasyGuide Neuro. After U-shaped opening of the

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Surg Neurol
1999;52:24 –9

Schreckenberger et al

PET/MRI-overlay demonstrates motor activated
brain areas behind and lateral to
tumor (A: transverse sections),
below tumor and in cerebellum
(B: sagittal sections).

2

dura perpendicular to the sagittal sinus, a smooth
and solid tumor was visible. The greyish tumor with
an opalescent surface and a firm-elastic consistency
was strongly adherent to the falx cerebri and the
lateral wall of the sagittal sinus (Figure 3). However,
the arachnoid layer of the adjacent precentral cortex was intact, and microsurgical dissection around
this cleavage plane was possible. Intraoperatively,
electrophysiological monitoring was performed
with a monopolar anodal electrical stimulus, delivered from a constant voltage stimulator (Viking IV,
Nicolet Biomedical Instruments, Madison, WI)
through a silver plate electrode of 1 cm2 contact
surface. One train of stimuli contained 5 pulses,
each of 100 ms duration. When stimulating the cortex at the back and lateral to the tumor, a repro-

ducible stimulus response in the muscle of the left
thigh and lower leg could be detected. Total resection of the lesion was possible without damaging
the sensorimotor cortex, and final electrophysiological stimulation elicited an unchanged stimulus
response in the above-described areas, and additionally in the area below the site of the tumor. The
postoperative course was uneventful; the moderate
hypoesthesia of the left leg during the first postoperative days disappeared completely. There was no
neurologic deficit when the patient was discharged
one week after the operation.
HISTOPATHOLOGY
Histologic examination of the tumor showed atypical cartilaginous tissue with moderate cell density

Preoperative PET activation in precentral chondroma

Surg Neurol
1999;52:24 –9

27

Intraoperative photograph
shows opalescent surface
of the chondroma and monopolar electrode for cortical stimulation at back of the tumor over
the motor cortex. Direct cortical
stimulation of this area induced
reproducible muscle contraction of left leg.

3

and predominantly small nuclei (Figure 4). Tumor
tissue showed numerous pyknotic nuclei but no
mitoses. The final histopathological diagnosis was
chondroma since a malignant chondrosarcoma was
ruled out by immunohistochemical staining (MIB I
against proliferation-associated antigene Ki 67: less
than 5% of the nuclei showed a positive immunohistochemical reaction).

Discussion
One of the main difficulties concerning the preoperative planning of precentral tumors is the exact
assessment of the spatial relationship between the

tumor and the functionally relevant brain areas. In
order to avoid irreversible damage from the approach or the resection procedure, exact anatomic
localization and functional monitoring are important. Slowly growing tumors may considerably displace the motor area without causing relevant
neurologic symptoms [3]. As a consequence, anatomical landmarks may be of little use in exactly
defining areas related to motor function in such
patients. In the case presented here, MRI showed a
tumor in the central sulcus area suggesting the
location of the primary motor cortex in front of the
tumor (Figure 1). In contrast, activation PET using a
simple motor activation task could reveal that the

Rather well-differentiated
and mature cartilaginous
tissue. Chondrocytes are in
bright cartilaginous areas, and
have small and round nuclei in
most cases. Most of the chondrocytes show slightly variable
size. Cells with double nuclei are
rare. (Magnification: 100 3)

4

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Surg Neurol
1999;52:24 –9

motor cortex area was shifted to the back by the
chondroma and was found at the rear of and below
the tumor. This finding was confirmed by intraoperative electrophysiological cortex stimulation,
which was regarded as the “gold standard” [3,11,
17]. This case demonstrates the clinical relevance
of PET activation studies providing a noninvasive
assessment of motor cortex area in patients with
precentral tumors. Thus, PET/MRI overlay increases safety in the preoperative planning of approach and microsurgical strategy. In the case presented here, the extra-axial tumor (chondroma)
was quite hypometabolic. The use of subtractive
FDG-PET activation studies in hypermetabolic intraaxial lesions (e.g., high-grade gliomas) may be
difficult due to partial volume effects, if the activated areas are very close to the hypermetabolic
tumor tissue. In these cases, the clinical benefit of
this method depends mainly on i) the full-width-athalf-maximum (FWHM) of the PET scanner and ii)
the quality of exact PET/MRI realignment. The PET
scanner we used in this study has a FWHM of 6 mm
in the x and the y direction, whereas the contact
surface of the monopolar electrostimulation probe
is 1 cm3. The image realignment tool used here has
a maximum axial translation variance of 2.2 mm [15]
which is considerably smaller than the FWHM of the
PET scanner and the spatial resolution of the stimulation probe, respectively. Herholz et al [5] evaluated the accuracy of preoperative localization of
language-related cortex by using 15O-water PET in
eight patients with left-side gliomas, and revealed a
sensitivity of 73% and a specificity of 81% in predicting aphasic symptoms during intraoperative
stimulation.
In the literature, very few case reports exist of
solitary chondromas of the falx and the convexity
dura with comparable neuroradiological image
studies [6,8,12] but none have included PET investigation. To date, there are few publications describing the clinical application of activation PET in
patients with cerebral tumors. They mainly concern
arteriovenous malformations [2,9,10,14]; few authors describe activation PET in glioma patients
[4,5]. In addition to PET, the first functional MRI
(fMRI) studies were reported for preoperative functional imaging in brain tumor patients [1,7,11]. In
contrast to PET, fMRI has a very low signal-to-noise
ratio, requiring multiple repeated measurements to
obtain sufficiently constant signals. Beyond this,
fMRI is very sensitive to motion artifacts during the
activation procedure, whereas F-18-fluorodeoxyglucose PET is less susceptible because acquisition
scan starts after activation is finished. However,
further comparative investigations are needed to

Schreckenberger et al

assess the validity and reliability of fMRI versus PET
in neurosurgical tumor patients.
The authors thank Professor A. Thron (Department of Neuroradiology, Aachen University of Technology) for providing
some of the MR images (Figures 1 A–C) and Dr. A. Rodon for
editorial services.

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COMMENTARY

The authors present a well-illustrated case of an
intracranial chondroma of the falx cerebri in which
they successfully mapped the adjacent motor cor-

Surg Neurol
1999;52:24 –9

29

tex before surgery using activated FDG-PET studies
fused with an MR scan. The PET findings were confirmed by intraoperative cortical mapping using direct cortical electrical stimulation. The techniques
described in this patient may be useful for preoperative mapping of the sensorimotor cortex and
have not previously been well characterized.
In this particular patient, the tumor was clearly
extra-axial and the preoperative imaging studies to
localize the sensorimotor cortex did not especially
improve the management of this patient. Also, the
tumor was very hypometabolic. This technique
would be most useful in the operative management
of patients with intra-axial lesions, especially those
that are not well demarcated from normal brain,
such as gliomas. As the authors point out in the
discussion, it is not clear how useful subtracted
FDG-PET images will be when a more metabolically
active intra-axial lesion is studied. Further studies
of a larger number of patients are needed to see if
this technique will be clinically useful.
Robert L. Grubb, Jr., M.D.
Department of Neurological Surgery
Washington University School of Medicine
St. Louis, Missouri

larger share of spending will go for health in the years ahead.
Demand for the latest lifesaving technologies will continue to
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other spending.

A

—“The Kiplinger Washington Letter”
December 23, 1998