From the Guidelines
Increased FDG uptake in the medial occipital lobes is typically a normal finding due to high glucose metabolism in the visual cortex, but can also indicate pathological conditions such as seizure activity or early neurodegenerative changes, as suggested by the most recent study 1. When interpreting PET images, qualitative and visual analysis is used to evaluate abnormal sites of increased uptake according to their intensity and uptake patterns, as described in the EANM/SNMMI guideline 1. In the context of increased FDG uptake in the medial occipital lobes, it is essential to consider the clinical context, patient symptoms, and comparison with normal baseline activity to determine the significance of this finding. The study by 1 highlights the importance of FDG-PET/CT in localizing epileptogenic foci, particularly in cases where MRI is negative, and demonstrates its predictive value for good surgical outcomes. Key points to consider when evaluating increased FDG uptake in the medial occipital lobes include:
- Clinical correlation with patient symptoms and neurological examination
- Comparison with normal baseline activity
- Consideration of potential pathological conditions such as seizure activity or early neurodegenerative changes
- Further diagnostic testing and interpretation by a neurologist to determine the relevance and necessity of intervention, as suggested by 1.
From the Research
Increased FDG in the Medial Occipital Lobes
- The "occipital tunnel" sign is a novel finding on FDG PET scans, characterized by relative sparing of FDG uptake in the medial occipital (primary visual) cortex compared to more severe loss in the surrounding lateral occipital (visual association) cortex 2.
- This sign is useful for recognizing the occipital findings of dementia with Lewy bodies and posterior cortical atrophy, especially when viewing sagittal projections 2.
- In patients with paraneoplastic neurological syndrome, increased FDG uptake in the occipital lobes has been observed, although this is not a common finding 3.
- One patient with paraneoplastic limbic encephalitis without antibodies had severely increased F-FDG uptake in both occipital lobes extending to the temporal lobes 3.
- Increased FDG uptake in the medial occipital lobes can be associated with various conditions, including dementia with Lewy bodies, posterior cortical atrophy, and paraneoplastic neurological syndrome 2, 3.
Possible Causes and Associations
- The "occipital tunnel" sign is associated with dementia with Lewy bodies and posterior cortical atrophy 2.
- Increased FDG uptake in the occipital lobes can be seen in patients with paraneoplastic neurological syndrome, particularly those with paraneoplastic limbic encephalitis 3.
- FDG uptake in the brain can be influenced by various factors, including age, neurological conditions, and medications 4, 5, 3, 6.
- It is essential to consider the clinical context and correlate FDG PET findings with other imaging modalities, such as MRI, to accurately interpret the results 5, 3, 6.