Diffusion-weighted imaging can correctly identify false-positive lymph nodes on positron emission tomography in...

One of the limitations of fluorodeoxyglucose-positron emission tomography (PET) for N-staging in non-small cell lung cancer (NSCLC) is false-positive results due to lymphadenitis. This study was performed to examine whether DWI can correctly identify false-positive nodes on PET in NSCLC.

Both PET and DWI were performed in 157 patients before surgery, which involved dissection of 1033 nodal stations. Of the 157 patients, 26 patients had pathological N1 or N2 disease. Each nodal station was classified as positive or negative on PET and DWI according to the cutoff value determined by the receiver operating characteristic curve. Short-axis diameters of lymph nodes were measured on computed tomography.

While hilar nodes did not show significant differences in the number of false-positives between PET and DWI, DWI showed fewer false-positives than PET in the mediastinum (p = 0.011). Of the 43 false-positive mediastinal nodes on PET, 35 (81 %) were negative on DWI. The mean size of the 43 false-positive nodes on PET was 9 ± 1 mm, which was significantly larger than mean size of 7 ± 3 mm of the 24 false-positive nodes on DWI (p = 0.002).

DWI can correctly identify false-positive nodes on PET in the mediastinum. The larger size of false-positive nodes on PET could be due to enlargement by lymphadenitis.