Q: All of the following may cause false negative positron emission tomography (PET) except?

A) tumor with low metabolic activity,
B) a small tumor,
C) hyperglycemia.
D) SIRS (Systemic Inflammatory Response System)
E) mucinous bronchioloalveolar cell carcinomas



Answer: D

PET scan should be read with caution as there may be very variables causing false positive and false negative results.

False positive results may occur due to active sepsis/SIRS, inflammatory lesions, or in rare case metabolically active brown fat or thymic tissue. In contrast, false negative tests may occur due to a tumor with low metabolic activity, a small size tumor, or hyperglycemia.


References: 

1. Jung Min Chang, MD, Hyun Ju Lee, MD, Jin Mo Goo, MD, Ho-Young Lee, MD, Jong Jin Lee, MD, -  False Positive and False Negative FDG-PET Scans in Various Thoracic Diseases -  Korean J Radiol. 2006 Jan-Mar; 7(1): 57–69. Published online 2006 Mar 31 

2. Cronin CG, Prakash P, Daniels GH, et al. Brown fat at PET/CT: correlation with patient characteristics. Radiology 2012; 263:836. 

3. Ferdinand B, Gupta P, Kramer EL. Spectrum of thymic uptake at 18F-FDG PET. Radiographics 2004; 24:1611.