Immunoglobulin G4-Related Disease Mimicking Meningioma and Dural Metastasis: A Case Report.

Herein, we report a case of immunoglobulin G4-related disease (IgG4-RD) that required differentiation from meningioma and dural metastasis based on neuroradiological imaging results, particularly focusing on magnetic resonance spectroscopy (MRS) and cerebral angiography findings. The patient was a 67-year-old woman who presented with left lower-limb weakness. She had been diagnosed with breast cancer 11 years earlier and was treated with surgical resection, followed by hormone therapy. Gadolinium-enhanced brain magnetic resonance imaging revealed a well-defined, homogeneously enhanced lesion accompanied by a dural tail sign. MRS revealed an increased choline peak with a high choline/N-acetylaspartate ratio and an elevated combined lipid/lactate peak. Based on these findings, a metastatic brain tumor or a malignant meningioma was initially suspected. Cerebral angiography demonstrated poor vascularity within the lesion. The tumor was resected. Part of the dura mater was significantly thickened due to involvement of the lesion, which also firmly adhered to the cortical surface. Histopathological examination with hematoxylin and eosin staining revealed a remarkable proliferation of collagen fibers and dense lymphocyte and plasma cell infiltration. Immunohistochemical staining showed an IgG4-/IgG-positive plasma cell ratio of 45%, with elevated levels of IgG4-positive plasma cells (40-50 per high-power field). A typical storiform pattern of fibrosis was not clearly observed. However, the presence of marked fibrosis and dense infiltration of IgG4-positive plasma cells led to the diagnosis of IgG4-RD. Even if MRS shows a tumor-like pattern, the identification of poor vascularity on cerebral angiography should prompt the consideration of IgG4-RD as a differential diagnosis, as in the current case.