Immunoglobulin g4-related hypertrophic pachymeningitis with skull involvement.

Immunoglobulin G4 (IgG4)-related hypertrophic pachymeningitis, defined as focally or diffusely thickened dura mater and lymphoplasmacytic infiltration with increased IgG4 bearing plasma cells, is a rare disease. Moreover, cases involving bone are even rarer. In this report, the authors describe a case of IgG4-related hypertrophic pachymeningitis involving the skull in a 65-year-old man presenting with generalized tonic seizures. There is a 2.4 cm diameter extra-axial mass at the vertex of the left frontal convexity and thickened dura mater with contrast enhancement on magnetic resonance (MR) imaging. In addition, the skull adjacent to the mass was focally enhanced. He underwent surgical resection of the enhanced mass and skull. Histopathological findings revealed chronic inflammation with fibrosis, and idiopathic hypertrophic intracranial pachymeningitis was considered. However, eight months after surgery, partial seizures developed and brain MR imaging revealed a recurrence adjacent to the previous mass. We decided to perform additional immunohistochemical staining of the previous specimen, instead of a re-excision. Immunohistochemical staining showed markedly increased IgG4 (+) plasma cells. Consequently, IgG4-related hypertrophic meningitis was confirmed. Since then, steroids and immunosuppressant medications were started. Follow-up MR imaging at 3 months after medication initiation demonstrated complete remission. In conclusion, IgG4-related hypertrophic pachymeningitis should be considered in the differential diagnosis of hypertrophic cranial pachymeningitis.