The role of FDG PET-CT in incidental lymphadenopathy

Objectives As CT imaging volume increases, incidentally found lymphadenopathy presents clinicians with a diagnostic dilemma as the work-up can be expensive and invasive but the rate of cancer is low. 18F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) has not been shown to aid in the diagnosis or risk stratification of cancer associated with incidental lymphadenopathy (IL) but our hospital has encountered an increasing number of PET-CT requests for IL work-up. The aim of this study was to characterize the utility of FDG PET-CT in the evaluation of patients with lymphadenopathy without other imaging findings of malignancy.

Methods The clinical indications for PET-CTs from 10/1/2008 to 9/30/2011 were searched for the key words “lymphadenopathy” and “lymph node”. Patients were included in the study if the indication for the PET-CT was initial evaluation of lymphadenopathy in the absence of current malignancy and other imaging findings of malignancy. The electronic medical records for patients were examined for PET-CT results, correlative imaging, prior medical history, pathologic results, referring clinician suspicion for cancer, and current health status.

Results Sixty-six PET-CT studies met the entry criteria. Ultimately, 15 of the 66 (23%) patients were diagnosed with malignancy. 9 of 10 (90%) patients with high clinical suspicion of cancer had a malignancy, but only 6 of 56 (11%) patients with low clinical suspicion of cancer had malignancy (p<0.0001). 41 (62%) patients had FDG avid lymph nodes; 14 of 15 (93%) of patients diagnosed with cancer exhibited FDG avid nodes. The sensitivity of PET-CT for malignancy was 93%, specificity 47%. The negative predictive value was 96%.

Conclusions FDG PET-CT has low specificity when evaluating lymphadenopathy without other imaging signs of malignancy. In the setting of high clinical suspicion of malignancy, FDG PET-CT may have a role in assessing disease extent and biopsy site determination. However, the data presented here suggest that for patients with low clinical suspicion of malignancy, follow up with conventional imaging is preferred