Given the patient's history and initial findings on CT, an ischemic stroke was the primary suspicion, with confirmatory MRI that led to a false conclusion that this indeed may be an unusually looking subacute MCA territory stroke, perhaps connected to previous endovascular treatment.

The follow-up scan did not show the expected typical evolution of findings, with only a moderate partial regression. 

Unusual appearance and lack of incongruence between symptoms, laboratory workup, and initially proposed imaging diagnosis, led to literature research and retrospective analysis of the imaging studies that associated the findings with the treatment the patient had undergone - the revised diagnosis was of "enhancing brain lesions after endovascular treatment". 

This is a rare and poorly understood condition suspected to be some kind of foreign body reaction and inflammatory changes with microembolic background and lack of larger vessel infarction. One of the cases described in the literature was autopsy-proven to show trapped particles/filaments of hydrophilic coating with granulomatous foreign body reaction.

Most of these lesions show up relatively late, which excludes typical acute/subacute ischemic etiology. The laboratory workup for patients, including the one in this case, showed no findings of CNS infection, effectively ruling out septic emboli.

Based on the imaging pattern and information in the literature, this appearance is most likely caused by a foreign body reaction with components of aseptic emboli and granulomas.