Background: Idiopathic hypertrophic pachymeningitis (IHP) is a rare clinical disease characterized by inflammatory fibrosis, which causes diffuse thickening of the dura mater. The inflammatory fibrosis will be locally invasive in nature but will be characterized by a benign histological appearance, known as an inflammatory pseudotumor. We present the case of a patient with an infiltrative lesion involving the right frontal convexity diagnosed as IHP, which had been suspected to be a malignant tumor or high-grade meningioma from the preoperative radiological findings.
Case description: A 59-year-old man was admitted to our hospital because of a temporary loss of consciousness. Contrast-enhanced magnetic resonance imaging (MRI) of the brain showed a 30-mm × 12-mm mass located in the right frontal convexity. The lesion had an isointensity to high-intensity signal with moderate periregional edema on T2-weighted MRI, and homogeneous enhancement, including a necrotic portion with a long dural tail along the right frontal convexity, after contrast-enhanced MRI. Thus, our preliminary diagnosis was high-grade meningioma or a malignant tumor. We decided to surgically remove the tumor. Intraoperatively, the lesion appeared as a dural-based yellowish mass with partial infiltration of the cortex. Histopathological examination of the lesion revealed thickened meninges with marked fibroinflammatory changes. The inflammatory changes extended into the underlying brain parenchyma and were centered in the perivascular spaces. The lesion showed abundant lymphoplasmacytic infiltration with fibrosis. Immunohistochemistry revealed mixed T and B lymphocytes and plasma cells. Only a small number of IgG4-positive cells were identified. From these findings, we finally concluded that the diagnosis was IHP. The patient did not receive any further steroid therapy, because the patient had no evidence of systemic autoimmune disease. A follow-up brain MRI scan was performed 6 month after surgery, which revealed no recurrence of the lesion.
Conclusions: Surgical treatment can be the first treatment option when the lesion is not localized to a critical portion of the brain. Thus, it might be possible to arrive at a definitive diagnosis histologically and determine additional treatment strategies. Also, if the surgeons are confident that the IHP has been removed completely, additional steroid therapy might not be necessary.
Keywords: Idiopathic hypertrophic pachymeningitis; Ig4; Meningioma; Pseudotumor; Tumefactive fibroinflammatory lesion.
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