Diagnostic performance of 18F-FDG PET-CT in patients presenting with secondary neck nodes from an unknown primary

Introduction: Clinical examination and even anatomical imaging may fail to identify primary site of malignancy in patients presenting with cervical nodal metastasis. 18F-Fluorodeoxyglucose Positron Emission Computed Tomography (18F-FDG PET-CT) is known to overcome the limitations of anatomic imaging. Methods: Sixty-three (63) patients (male:female=55:8, age range=32-83 years, mean age=61.14 ±12.6 years) with one or more metastatic neck node (s) from occult primary underwent 18F-FDG PET-CT. Nodal cytological/biopsy findings, IHC of cervical nodal biopsy (whenever available), scan findings, subsequent biopsy findings (PET guided/ directed)  of suggested occult primaries were correlated. Subsequent detection of any primary malignancy in whom 18F-FDG PET-CT failed to localize a primary was also documented. Results: Malignancy was confirmed in eighteen (18) out of those twenty-four (24) patients in whom site of possible occult primary malignancy was suggested out of total sixty-three (63) patients. In five (5) patients out of remaining thirty-nine (39) patients, a site of primary malignancy was detected or a site of primary malignancy was considered based on IHC subsequently. The detection rate of occult primary, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and false positivity rate was calculated to be 28.5%, 78.2%, 85%, 75%, 87.1% and 15% respectively. 18F-FDG PET-CT also detected other lymph nodal and organ metastases in 46% and 23.8% patients respectively. Conclusion: 18F-FDG PET-CT is a useful modality for detecting unknown primary and other nodal /distant metastases in patients presenting with neck nodal metastases.