Large dural-based mass with bony hyperostosis in a 16-year-old male: IgG4-related disease mimicking lymphoplasmacyte-rich meningioma.

IgG4-related disease is an autoimmune process that presents with tumefactive lesions characterized by storiform fibrosis, a dense lymphoplasmacytic infiltrate rich in IgG4+ plasma cells, obliterative phlebitis, and often elevated serum IgG4 levels. Central nervous system IgG4-related disease is very rare and usually occurs in the form of hypertrophic pachymeningitis or hypophysitis. Presentation as a large solitary meningioma-like mass with overlying hyperostosis in a young adult has not been reported before.A 16-year-old male presented with focal seizures for 5 months. Imaging showed a large, extra-axial, and contrast-enhancing mass lesion in the left frontoparietal region with focal calvarial thickening. Histopathology revealed a fibrosclerotic lesion involving dura with a polymorphic infiltrate of plasma cells, mature lymphocytes, histiocytes, and occasional eosinophils. Immunohistochemical workup excluded the possibilities of meningioma, lymphoproliferative neoplasms, and histiocytic lesions. Majority of plasma cells were IgG4+ rendering a diagnosis of IgG4-related disease. Further serological and imaging workup did not reveal any evidence of systemic involvement. His serum IgG4 levels were normal. Considering a gross total resection of the lesion, no further treatment was given and the patient has been asymptomatic since.IgG4-related lesions of the CNS are under-recognized and accurate diagnosis, especially in those with isolated CNS disease and normal serum IgG4 levels, necessitates robust histopathological and laboratory workup to exclude mimics. They may occur as large dural masses with hyperostosis and differentiation from lymphoplasmacyte-rich meningiomas, in particular, can be challenging. While steroids are the mainstay of treatment in IgG4-related disease, surgical resection may be curative in solitary lesions presenting with compressive symptoms.