Lung Cancer.pdf

42 R.F. Munden and J.J. Erasmus
(Gupta et al, 1992; Dewan et al, 1993; Patz et al, 1993; Knight et al, 1996;
Gould et al, 2001). False-negative results are uncommon; however, at
M.D. Anderson, serial radiologic assessment is performed for 2 years on
all opacities with low FDG uptake that are not biopsied or resected. Low
FDG uptake has a high specificity in the diagnosis of benign lesions and
can substantially reduce the number of unnecessary biopsies and surgical
resections performed. However, false-positive results can occur with infection
and inflammation (e.g., lesions due to tuberculosis, histoplasmosis,
or rheumatoid arthritis).
Preliminary studies evaluating solitary lung opacities also suggest a
possible role of FDG-PET as a prognostic indicator (Ahuja et al, 1998; Dhital
et al, 2000). Patients with significantly increased FDG uptake in the primary
lesion have a worse survival rate than that of patients with modest
FDG uptake. The concentration of FDG within a nodule can be measured
on attenuation-corrected, quantitative PET images. FDG uptake is usually
expressed as the standardized uptake value, also referred to as the differential
uptake ratio. This semiquantitative measure is calculated by dividing
the mean activity of the nodule by the injected dose and multiplying
the result by the body weight—i.e.,
Standardized Uptake Value
Mean Activity of Nodule (mCi/mL) Body Weight (kg)
Injected Dose (mCi)
Image-Guided Transthoracic Needle Aspiration Biopsy
Many lesions have indeterminate etiology even after comprehensive radiologic
assessment. These lesions can be observed, biopsied, or resected. The
choice of approach is usually subjective and based on the perceived probability
that the opacity is malignant (according to clinical parameters such
as the patient’s age and cigarette-smoking history as well as the radiologic
features of the nodule).
Advances in CT and cytopathology have led to an expanded role for
image-guided transthoracic needle aspiration (TTNA) biopsy in the diagnostic
evaluation of thoracic lesions. TTNA biopsy is now widely accepted
as a safe, accurate procedure with a high yield in establishing the diagnosis
of pulmonary and mediastinal masses. TTNA biopsy has been
shown to frequently alter management in patients with lung cancer and, if
the likelihood of malignancy is low, is the best initial diagnostic procedure
(Klein and Zarka, 1997). In the case of peripheral opacities, TTNA should
be used instead of bronchoscopy because TTNA is more likely to yield a
diagnosis. Most radiographically visible lesions can be biopsied with a
TTNA approach if biopsy is clinically indicated.
TTNA biopsy has a high sensitivity for the diagnosis of malignancy,
and even in the case of small lesions (10–15 mm in diameter) the yield is