Spontaneous remission of a massive CNS inflammation with eosinophilic infiltrate

We report a case of spontaneous remission of a massive CNS lesion with eosinophilic infiltrate. This 69-year-old man had eosinophilia without any systemic disorder or laboratory evidence of the most common causes of hypereosinophilia. MRI of the brain suggested an infiltrating neoplasm, but histological examination of a needle biopsy specimen failed to show evidence of a neoplasm. Instead, the tissue demonstrated rarefaction and gliosis with striking perivascular and parenchymal infiltrates of eosinophils. The MRI abnormality and eosinophilia disappeared spontaneously. We speculate that eosinophil-derived neurotoxins might have been the cause of the transient CNS disorder observed in this patient.