This case outlines IgG4-RD manifesting as an enhancing left temporal mass in a man who presented with the symptoms of confusion and headaches. Also emphasis on the responsiveness to rituximab as a treatment modality to prevent recurrence.

IgG4-RD is a systemic disease characterized by fibroinflammatory changes with infiltrations of IgG4-predominant plasma cells and eosinophils. Nervous system involvement is observed less frequently, and instances of brain parenchymal involvement, as demonstrated in this case, are even rarer, with most cases manifesting as hypertrophic pachymeningitis, and inflammatory lesions of the pituitary gland. Our case involved lung nodules which resolved after treatment, making the diagnosis crucial as they can be mistaken for infections or malignancy. This case highlights the successful management through surgical resection, corticosteroids, and rituximab.