A 37-year-old woman with a history of thyroid carcinoma, status post thyroidectomy and I-131 therapy, presented with multiple pulmonary nodules and mediastinal/hilar lymphadenopathy on a computed tomography (CT) scan of the chest.
A 37-year-old woman with a history of thyroid carcinoma, status
post thyroidectomy and I-131 therapy, presented with multiple
pulmonary nodules and mediastinal/hilar lymphadenopathy on a
computed tomography (CT) scan of the chest. This patient was
currently taking Synthroid (Abbott Laboratories, Abbott Park, IL).
Laboratory data were unremarkable and physical examination revealed
mild shortness of breath. A whole-body positron emission tomography
(PET) scan was performed on a dedicated GE Advance PET scanner (GE
Medical Systems, Waukesha, WI) approximately 1 hour after the
injection of 14.8 mCi of 18 fluorine-fluorodeoxyglucose (FDG)
The whole-body FDG PET scan revealed FDG-avid lymph nodes in the
hila and mediastinal regions. The pulmonary nodules noted on the CT
scan were not metabolically active. Mediastinoscopy with lymph node
biopsy was subsequently performed. Pathologic evaluation revealed
findings compatible with sarcoidosis.
Positron emission tomography scanning has established itself as
a standard tool in the evaluation and follow-up of oncology
patients. Until recently, issues such as cost and extremely short
isotope half-life had limited PET scanning primarily to research
centers. Positron emission tomography scanning has exploded, and
this modality has firmly rooted itself even within the private
A vast experience with PET scanning is still evolving. As with
any new technique, a learning curve is expected. An essential
knowledge of normal excretion, uptake, and normal variations of
distribution of radiotracer, as well as technical artifacts, is
critical in the correct interpretation of PET images.
FDG uptake can be seen in a number of benign lesions, including
infectious and inflammatory processes, leading to false-positive
Benign lesions that have been found to take up FDG are chronic
thyroidosis, Warthin's tumor of the parotid, and chronic sinusitis.
In the chest, false-positive findings can be seen with sarcoidosis,
active tuberculosis, granuloma, thymoma, pneumonia, and abscess.
Less common etiologies causing false-positive findings include
thymic hyperplasia, aspergillosis, histoplasmosis, rheumatoid
disease, alveolitis, and radiation pneumonitis.
Most patients with sarcoidosis are discovered incidentally by
abnormal radiographic findings on chest X-ray. However, as in this
case, incidental diagnosis on whole-body FDG PET scanning is being
reported with increased frequency. The increased FDG uptake is
thought to be related to the actively dividing macrophages,
lymphocytes, and epithelial monocytes that comprise sarcoid
It should be noted that the pattern of uptake in sarcoidosis can
overlap that of lymphoma on a PET scan. Other clinical and
radiographic findings will help differentiate these two
Although Gallium citrate scanning has classically been used to
diagnose and monitor disease activity in patients with sarcoidosis,
recent use of FDG PET as an inflammatory marker has been
investigated in patients with known sarcoidosis. Parenchymal uptake
has also been reported in patients with sarcoidosis, which, along
with the uptake in the associated lymphadenopathy, returned to
normal after steroid therapy.
This may lead to a role for FDG PET scanning in monitoring patients
FDG PET scanning has been shown to be an effective tool in the
physician's diagnostic arsenal and is playing an increasingly
important role in the follow-up of oncology patients. The
radiologist must become familiar with the multitude of potential
false-positive findings in order to accurately interpret PET