Potential pitfalls of 18F-FDG PET in a large series of patients treated for malignant lymphoma: prevalence and scan interpretation.
OBJECTIVE
To evaluate the prevalence and scan interpretation criteria useful in identifying non-tumoural F-FDG focal uptakes (potential pitfalls) in patients who had been previously treated for a malignant lymphoma studied by positron emission tomography (PET).


METHODS
Nine hundred and ninety-six consecutive PET scans obtained in 706 patients with malignant lymphoma were reviewed. All patients had been previously treated by first-line chemo-radiotherapy, plus surgery when required, and were then studied by FDG PET to investigate suspected recurrence at doubtful or inconclusive conventional radiological imaging (ultrasound, computed tomography, magnetic resonance imaging). PET was obtained with patients in the fasted condition and after i.v. injection of 370 MBq of F-FDG; imaging was acquired 60-90 min later. In patients with focal FDG uptake the final diagnosis was reached on the basis of histological findings or long-term follow-up.


RESULTS
Thirty-one of 134 PET scans (23.1%) showing focal FDG uptake were diagnosed as non-tumoural radiotracer uptake, related to the presence of brown fat in seven cases, thymic hyperplasia in five, muscles contraction in four, lymph node unspecific inflammation in four, mediastinal/pulmonary unspecific inflammation in four, gastritis in two, colitis in two, bacterial abscess in one, lactating breast in one, and herpes zoster in one. Each of the above cited situations has been reported in the literature, generally in the form of sporadic reports, as a potential cause of misinterpretation (false positive) in reading a PET scan with the potential for incorrect patient management. An accurate diagnosis in these patients was important for the following therapeutic decision making.


CONCLUSIONS
In the whole series of patients with treated malignant lymphoma, the prevalence of non-tumoural FDG focal uptake during follow-up was relatively low (3.1%); conversely, it was relatively high when considering the sub-group of 'positive' PET only (23.1%). The importance of knowing these situations in order to avoid misinterpretation in reading PET scans needs to be emphasized. In this light, an accurate patient's history and a skilful nuclear medicine physician are very important factors. For the same purpose, it is reasonable to think that the use of hybrid PET/CT tomographs could also play an important role in helping to identify non-tumoural FDG focal uptake.
Nuclear Medicine Department, S. Orsola-Malpighi Hospital, Bologna, Italy.
Paolo
P
Castellucci
Cristina
C
Nanni
Mohsen
M
Farsad
Lapo
L
Alinari
Pierluigi
P
Zinzani
Vittorio
V
Stefoni
Giuseppe
G
Battista
Daria
D
Valentini
Cinzia
C
Pettinato
Mario
M
Marengo
Stefano
S
Boschi
Romeo
R
Canini
Michele
M
Baccarani
Nino
N
Monetti
Roberto
R
Franchi
Lucia
L
Rampin
Stefano
S
Fanti
Domenico
D
Rubello
D016477:Artifacts; D003951:Diagnostic Errors / Q000517:prevention & control* / Q000706:statistics & numerical data*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008223:Lymphoma / Q000000981:diagnostic imaging* / Q000453:epidemiology* / Q000628:therapy; D015588:Observer Variation; D049268:Positron-Emission Tomography / Q000706:statistics & numerical data*; D015995:Prevalence; D011379:Prognosis; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18