Prevalence of Detecting Unknown Cerebral Metastases in Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography and its Potential Clinical Impact

To determine the prevalence of incidental finding of unknown cerebral metastases and explore the clinical impact of detecting unknown brain metastases among individuals underwent whole body fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) with brain included in field of view. A retrospective review of 1876 patients who underwent whole body PET/CT examination in our clinical PET center for oncological evaluation from January 2009 to September 2009 was performed. The total number and prevalence of unknown brain metastases detected by PET/CT were calculated. Patients diagnosed with cerebral metastases by PET/CT were further analyzed via the electronic patient record system for relevant clinical and radiological findings. Positive predictive value of PET/CT for the diagnosis of cerebral metastases was calculated with reference to contrast enhanced magnetic resonance imaging (MRI) or contrast enhanced CT. Of the 1876 subjects, 71 patients (3.8%) were diagnosed with cerebral metastases by PET/CT. 31 patients were already diagnosed with brain metastases before PET/CT. Among the 40 patients with unknown brain metastasis, 24 (60.0%) underwent either MRI (n = 5) or CT (n = 19) after PET/CT, of which 17 patients were confirmed with cerebral metastases. The true positive rate was 70.8% (17/24), while the false positive rate of PET/CT was 29.2% (7/24). Nearly 94.1% (16/17) patients with confirmed cerebral metastases on MRI or CT had subsequent change in management. Among the remaining 16 patients with positive findings of cerebral metastases without further radiological correlation, 43.8% (7/16) patients had change in management after PET/CT. A total of 57.5% (23/40) patients had change in management after PET/CT. The point prevalence of detecting unknown cerebral metastases by PET/CT was 2.1% (40/1876). 94.1% patients with newly diagnosed brain metastases confirmed with either MRI or CT received immediate treatment for cerebral metastasis in this retrospective study. PET/CT demonstrated significant clinical impact by identifying cerebral lesions with mass effect and hence that timely treatment was offered.