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Findings: The fluorine-18 ion PET scan shows F-18 uptake at L-4, T-9 and T-10. The FDG scan shows uptake at L-4 and periphery of the patient's chest lesion. Superimposition of the MRI, F-18 ion and FDG images demonstrates the L-4 abnormality on all three modalities indicating metastatic disease. The negative FDG and MRI scans at T-9 and 10 suggest that this area of abnormal fluorine-18 ion uptake is due to benign disease.
Diagnosis: Metastatic lesion at L-4 and residual/recurrent tumor within the chest.
Discussion:Bone scanning is the primary modality for the diagnosis of metastatic disease to bone. In patients with bronchogenic carcinoma, a positive bone scan is a poor prognostic sign. In one study, survival correlated with bone pain and an abnormal bone scan. Bone metastasis in lung cancer can also have an unusual distribution, such as, abnormalities in the appendicular skeleton including the hands and feet. This patient presented with bone pain, but an initially negative work-up. The pain continued and further work-up with PET was performed because of the impact of metastatic disease on a patient's prognosis.
Fluorine-18 ion has been used as a skeletal imaging agent for many years. It has a high lesion to normal bone ratio and is rapidly cleared from soft tissues and blood giving a high bone to background ratio. It was used in this case to increase the likelihood of detecting subtle abnormalities which were missed on the initial technitium-99mMDP bone scan. F-18 FBG was used to determine which lesion seen with F-18 ion represented neoplastic disease. Malignant cells have an enhanced rate of glycolysis, an effect first noted by Warburg in 1930. Imaging with FDG and PET takes advantage of this fact to detect tumor. A whole-body scan can be used as a screen for metastatic disease. In this patient only the abnormality at L-4 seen with fluorine-18 ion showed FDG avidity consistent with tumor. This abnormality at L-4 was also seen on a second MRI scan. The FDG scan also documented residual and/or recurrent tumor within the chest.
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