La PET con 18-fluorodesoxiglucosa (18F-FDG-PET) es una técnica cuantitativa con la esperanza sustancial puesta en el estadiaje y evaluación de sarcomas de los tejidos blandos. La PET, que mide la actividad metabólica de la glucosa, proporciona una información funcional de la lesión. Con esta técnica se puede descubrir extensión local insospechada o diseminación a distancia y suele preceder y complementar a las técnicas morfológicas de imagen (Rx, TAC, y RNM). Permite hacer cortes sagitales y transversales y con ello un mejor estudio loco-regional. En un informe, la sensibilidad de la PET Scan para el descubrimiento de sarcomas del tejido blando era del 100 por ciento.
En las lesiones malignas hay una acumulación de fluorodeoxigluosa por aumento en la glucólisis anaeróbica. Hay correlación entre el grado de malignidad y la tasa de consumo de FDG, por tanto la PET también puede distinguir las lesiones benignas y las lesiones de alto grado; sin embargo, su capacidad para diferenciar lesiones benignas y de bajo grado a intermedio está limitada. La sensibilidad para los sarcomas de grado bajo parece ser menor que para intermedio o los tumores de grado altos. Además, la magnitud de la reducción en la actividad metabólica de la glucosa puede usarse para estimar el grado de necrosis inducido por la radiación y quimioterapia, proporcionando un método no invasivo de evaluar la respuesta. También se ha mostrado útil para predecir los tumores que van a responder bien o mal a la quimioterapia, así como para la detección de las metástasis y la distinción entre recidiva tumoral y fibrosis posquirúrgica.
Indicaciones de la PET
Establecimiento el grado histológico del tumor. A mayor grado histológico corresponde mayor captación de 18F-FDG. Sin embargo las lesiones de bajo grado son difíciles de distinguir de las lesiones benignas.
Bibliografía
Comparison
and
discrepancy
of
18F-2-deoxyglucose
positron emission tomography and
Tc-99m
MDP
bone scan to
detect
bone
metastases. Anticancer
Res
2000
May-Jun;20(3B):2189-92 (ISSN:
0250-7005)
Kao
CH;
Hsieh
JF;
Tsai
SC;
Ho
YJ;
Yen
RF
Department
of
Nuclear
Medicine,
Taichung
Veterans
General
Hospital, Taiwan.
The
purpose
of
this
study
was
to
evaluate
the
usefulness
of
positron emission tomography with
18F-2-deoxyglucose
(FDG-PET)
for
the
detection
of
malignant
bone
metastases,
and
to
compare
FDG-PET results
with
conventional
technetium-99m
methylene
diophosphate
(Tc-99m
MDP)
bone scan findings.
Twenty-four
patients
(10
females,
14
males,
ages:
39-71
years)
with
biopsy-proven
malignancy
and
suspected
bone
metastases,
underwent
whole
body
FDG-PET and
bone scan to
detect
bone metastases.
Bone
metastases
were
established
in
39
discordant
bone
lesions
by
histopathological
examination
of
biopsy
samples,
MRI/CT,
and
follow-up
bone scan/FDG-PET findings
showing
progressively
and
extensively
widespread
bone
lesions.
A
total
of
98
bone
lesions
found
on
either
FDG-PET or
bone scan were
evaluated
For
39
bone
lesions
with
discordant
findings
between
FDG-PET and
bone scan,
histopathological
examination, MRI/CT
and
follow-up
bone scan/FDG-PET findings
revealed
8
metastatic
and
0
benign
bone
lesions
with
positive
FDG-PET findings,
not
detected
on
bone scan.
Eleven
metastatic
and
20
benign
bone
lesions
with
positive
bone scan findings
were
not
detected
on
FDG-PET.
FDG-PET has
a
better
specificity,
but
a
lower
sensitivity
for
detecting
malignant
bone
metastases
when
compared
with
bone scan.
Differentiating
recurrent
tumor
from
radiation
necrosis:
time
for
re-evaluation
of
positron emission tomography?
[see
comments]
|
AJNR
Am
J
Neuroradiol
1998
Mar;19(3):407-13 (ISSN:
0195-6108)
Ricci
PE;
Karis
JP;
Heiserman
JE;
Fram
EK;
Bice
AN;
Drayer
BP
[Find
other
articles
with
these
Authors]
Department
of
Neuroradiology,
Barrow
Neurological
Institute,
Phoenix,
AZ
85001,
USA.
Our
purpose
was
to
evaluate
the
ability
of
FDG PET to
differentiate
recurrent
tumor
from
posttherapy
radiation
necrosis.
METHODS:
MR
images, PET scans,
and
medical
records
of
84
consecutive
patients
with
a
history
of
a
treated
intracranial
neoplasm
were
evaluated
retrospectively.
In
all
patients,
recurrent
tumor
or
radiation
necrosis
was
suggested
by
clinical
or
MR
findings.
Metabolic
activity
of
the PET abnormality
was
compared
qualitatively
with
normal
contralateral
gray
and
white
matter.
RESULTS: PET findings
were
confirmed
histologically
in
31
patients.
With
contralateral
white
matter
as
the
standard
of
comparison,
the PET scan sensitivity
and
specificity
were
found
to
be
86%
and
22%,
respectively.
With
contralateral
gray
matter
as
the
reference
standard,
the
sensitivity
and
specificity
became
73%
and
56%,
respectively.
Overall,
nearly
one
third
of
the
patients
would
have
been
treated
inappropriately
in
either
scheme
had
the PET scan been
the
sole
determinant
of
therapy.
CONCLUSION:
Our
data
suggest
that
the
ability
of
FDG PET to
differentiate
recurrent
tumor
from
radiation
necrosis
is
limited.
Both
false-positive
and
false-negative PET scan results
contributed
to
unacceptably
low
sensitivity
and
specificity
values