Based on imaging alone, what is the single most important other entity to consider in your differential diagnosis?
Solitary metastasis.
What finding is pathognomonic of brain abscess?
None! The clinical data and the imaging findings are your guide for a better diagnosis. Visit the page of "cerebral ring enhancing lesions".
There is a space-occupying lesion situated at the right parietal lobe. It has an irregular border that is low signal on T2 images. The centre of the lesion is intermediate on T1 and hyperintense on T2 images. The lesion is surrounded by voluminous vasogenic oedema that distorts and expands the lobe and results in brain structures shift into the contralateral side. On the ADC map, the lesion shows diffusion restriction due to a centre of viscous pus. On the post-contrast images, the lesion shows wall enhancement in the so-called ring pattern.
Changes of sinusitis are also seen in the left maxillary sinus.