Answer. Left occipital lobe mass (metastasis) with vasogenic edema.

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This case is challenging for a couple reasons. A (subsequently) pathologically confirmed lung adenocarcinoma metastasis is present, but it is difficult to distinguish from the adjacent occipital lobe cortex in this case. To be fair, it was easier to detect with some adjustments of w/l sessions (but one would need to suspect it was there in the first place to prompt further scrutiny). Additionally, edema in the region of the occipital horns of the lateral ventricles can be challenging to detect.

One effective method to enhance CT interpretation is to first view a CT without the benefit of MRI data and later review it again with the benefit of MRI data. This use pattern of viewing CT data alone, then MRI data, and finally re-revisiting the CT data is a key concept of 360° Neuroradiology.