A Quick Review of the Brain
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Her PET-CT scan revealed Metastatic Retroperitoneal Lymph nodes suggesting recurrence. The brain images revealed a hypometabolic area in the right frontal lobe with a hyperdense rim on CT correlate with surrounding vasogenic edema representing a likely metastatic lesion. As cystic metastasis do not show FDG avidity, an MRI was advised which revealed rounded abnormal signal intensity area appearing hyperintense on T2W images with peripheral rim of hypointense signals and perilesional edema suggestive of metastases (Figure 3). Discussion Metastases to the brain can affect about 10%-20% cancer patients especially those with cancers of the lung, breast. Greater understanding and advances towards treatment associated with better and more sensitive diagnostic imaging technique have led improved survival rates and hence more cases of delayed brain metastasis [3,4]. Early detection of brain involvement is essential so help in curbing the therapeutic strategy and ascertain prognosis. Though contrast enhanced MRI remains the mainstay in the diagnosis, Computerized Tomography (CT) has also been deployed to assess metastasis. These modalities are however used when there is suspicion, symptoms or risk for the brain metastasis [5-7]. Positron emission tomography using FDG has been used for staging and restaging of several cancers. It has been recommended as the first line imaging modality in staging, restaging, response assessment and follow-up of different cancers. Both the SNMMI and EANM procedural guidelines for an oncological PET scan acquisition confer on imaging the body from the base of the skull to the mid thighs (“from the eyes to the thighs” or the “lips to the hips”), unless otherwise indicated for tumors that show a high probability of metastases in the head, skull, brain and lower extremities [8]. Brain metastases, if seen on the PET-CT scanning, are identified as discrete hypermetabolic or hypometabolic foci relative to the FDG uptake in the grey matter [7]. The role of FDG PET in the detection of brain metastasis has been often questioned in literature and found to be limited. The reasons cited in literature for exclusion is that a total of 7% of the injected activity is taken up by the brain as the it exclusively uses glucose for all its metabolic functions, hence any lesion within this high background will ultimately be masked or lost altogether [5,6,8]. Also, there is a relatively lower sensitivity of FDG for brain metastases, due to limited spatial resolution of PET scanners [3]. Still there have been studies that have shown that inclusion of the head in the FDG PET-CT has benefits to offer in terms of identifying lesions in the region and aid in the further management of the studies [7]. The acquisition protocols at our center dictate image acquisitions to include the skull, and we have presented here cases showing the advantage of such a protocol where lesions were identified in the brain in patients who either had no symptoms or vague symptoms for the same. The lesions identified led to further investigation for the patients with the gold standard modality MRI for confirmation of the lesions. MRI in all three cases confirmed the initial diagnosis of brain lesion and led to modification of treatment regimen