To evaluate the clinical implications of lymph node (LN) density on F-FDG PET/CT for mediastinal LN characterization in non-small cell lung cancer (NSCLC).

One hundred and fifty-two patients with 271 mediastinal LNs who underwent PET/CT and endobronchial ultrasound-guided transbronchial needle aspiration for staging were enrolled. Maximum standardized uptake value (SUVmax), short axis diameter, LN-to-primary cancer ratio of SUVmax, and median Hounsfield unit (HU) based on CT histogram were correlated to histopathology.

Of 271 nodes, 162 (59.8 %) were malignant. SUVmax, short axis diameter, and LPR of malignant LNs were higher than those of benign nodes. Among malignant LNs, 71.0 % had median HU between 25 and 45, while 78.9 % of benign LNs had values <25 HU or >45 HU. Using a cutoff value of 4.0, SUVmax showed the highest diagnostic ability for detecting malignant LNs with a specificity of 94.5 %, but showing a sensitivity of 70.4 %. Using additional density criteria (median HU 25-45) in LNs with 2.0< SUVmax ≤4.0, the sensitivity increased to 88.3 % with the specificity of 82.6 %.

LN density is useful for the characterization of LNs with mild F-FDG uptake. The risk of mediastinal LN metastasis in NSCLC patients could be further stratified using both F-FDG uptake and LN density.

• SUVmax showed the highest diagnostic ability for detecting malignant LNs. • LN density was useful in characterization of LNs with mild FDG uptake. • SUVmax and LN density together could stratify the risk of LN metastasis.