Abstract
Positron emission tomography (PET) using O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET has been shown to be a useful tool for differentiating radiation therapy outcomes, such as brain metastasis recurrence or radiation necrosis. We present the case of a female patient with brain metastases from pulmonary mucinous adenocarcinoma with suspicion of tumor recurrence on follow-up magnetic resonance imaging (MRI) after radiosurgery. 18F-FET PET/computed tomography (CT) was indicative of radiation necrosis. Due to the patient's medical history and the discrepancy between the brain MRI and PET/CT results, surgical biopsies were decided, which were positive for brain metastasis recurrence. The diagnosis of metastasis recurrence may also be challenging on 18F-FET PET/CT. In case of discrepancies between MRI and PET/CT results, false-negative 18F-FET PET/CT remains a possibility and requires careful follow-up or biopsy.
Highlights
O-(2-[18F]fluoroethyl)-L-tyrosine Positron emission tomography (PET) (18F-FET) is an artificial amino acid taken up by upregulated tumor cells but not incorporated into proteins. 18F-FET positron emission tomography/computed tomography (PET/CT) is increasingly used in daily practice, especially in the imaging of primary brain tumors and metastatic lesions
We present a case of false-negative 18F-FET PET/CT examination in a patient with treated brain metastases from pulmonary mucinous adenocarcinoma
Magnetic resonance spectroscopy (MRS) is an ongoing subject of research and may show that N-acetyl aspartate (NAA) and creatinine (Cr) decrease in cases of radiation necrosis, whereas high choline (Cho) levels are correlated with tumor recurrence (Rock et al 2004; Sundgren et al 2006)
Summary
O-(2-[18F]fluoroethyl)-L-tyrosine PET (18F-FET) is an artificial amino acid taken up by upregulated tumor cells but not incorporated into proteins. 18F-FET positron emission tomography/computed tomography (PET/CT) is increasingly used in daily practice, especially in the imaging of primary brain tumors and metastatic lesions. Surgical biopsies were decided after multidisciplinary discussions and showed the lesion corresponding to the tumoral tissue residue This case illustrates that published cut-off values of 18F-FET parameters might not be appropriate for evaluating treated brain metastases from every cancer type in daily practice. Case report A 58-year-old woman with cerebral metastases from lung cancer of the right upper lobe presented with the progression of lesion size on follow-up MRI She was initially diagnosed with mucinous adenocarcinoma 4 years previously, which was confirmed after a bronchoscopic biopsy and staged cT1a (0.6 cm) cN2 (station 4R) cM1c (five brain metastases), stage IVB (according to the TNM 8th edition). No significant radiotracer uptake was observed in the other metastatic lesions treated with radiosurgery In this context, her case was re-discussed at the multidisciplinary brain metastases board, where surgical resection of the right frontal lesion was proposed. Histopathological analyses of excisional biopsies of the lesion confirmed metastatic recurrence of her initial mucinous adenocarcinoma, while the dura mater biopsies showed no metastatic cells; revealed chronic calcified inflammatory reaction with foreign bodies
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