Isolated FDG uptakes of axillary lymph nodes identified on PET/CT: Clinical significance and sonographic correlation

Objectives The purpose of this study was to evaluate the clinical significance and the usefulness of sonography for axillary lymph nodes with isolated 18F-fluorodeoxyglucose (FDG) uptakes identified on whole body positron-emission tomography/computed tomography (PET/CT).

Methods Institutional review board approved this retrospective study and waived informed consent. From 11713 patients who underwent whole-body FDG PET/CT at our institution from February 2004 to March 2011, 33 patients underwent subsequent axillary sonographic examinations due to isolated FDG uptakes of axillary lymph nodes on PET/CT. Patients without biopsy proven results or long-term imaging follow-up (n=9) were excluded. A total of 24 patients were included.

Results The overall intensity of FDG uptake on PET/CT in 24 patients was a mean maximum SUV (SUVmax) of 3.28 (range, 1.3-8.28). Finally, malignancy was diagnosed in 6 patients (25%). The mean SUVmax measured in 6 patients was 5.67 (range, 3.02-8.28). Sonographic features of involved axillary lymph nodes in 6 patients were all malignant. In 18 (75%) of 24 patients, axillary lymph nodes were defined as benign. The mean SUVmax measured in benign lesions was 2.50 (range, 1.3-3.6). Sonography showed axillary lymph nodes suspicious for malignancy in 3 of 18 patients and for benign in 15. The sensitivity, specificity, PPV and NPV of sonography for detecting malignant axillary lymph nodes are 100%, 83.33%, 66.67% and 100%, respectively.There was a statistically significant difference in SUVmax between malignant and benign axillary lymph nodes (5.67±2.2317 vs 2.50±0.6215, p<0.0001). By ROC curve analysis, the optimal cut-off level of SUVmax on PET/CT for malignant axillary lymph nodes was 3.01.

Conclusions Axillary lymph nodes with isolated FDG uptakes on whole body PET/CT showed low risk of malignancy (25%). Axillary lymph nodes with a SUV greater than 3.01 were malignant. Subsequent sonographic evaluation was useful to improve the specificity in assessment of these axillary lymph nodes