Dear Editor, We want to present a rare case of an intracranial bifrontal mass lesion in a woman with rheumatoid arthiritis, which was originally interpreted as an intracranial malignancy. Central nervous system involvement in rheumatoid arthritis is rare, but can occur as vasculitis, pachymeningitis (involving the dura mater) and leptomeningitis (involving the pia mater and arachnoid mater). To the best of our knowledge, only approximately 25 cases of rheumatoid meningitis have been reported thus far (e.g., [1–10]). The reported patients in the literature presented with a broad spectrum of neurological complaints including seizures, headache, confusion, nausea and focal deficits including cranial nerve palsy [7]. The key feature onMR imaging is diffusemeningeal enhancement.We report on rheumatoid pachymeningitis presenting on MR imaging as a multinodular mass lesion, suggestive of an intracranial malignancy. A 56-year-old woman with a history of poorly regulated rheumatoid arthritis presented with tonic-clonic seizures in a non-teaching hospital. The MR imaging revealed a frontal lesion of the falx dura with central cysts, bifrontal extensions and enhancement after administration of gadolinium. There was perifocal white matter edema frontally in both hemispheres. The lesion showed mass effect (Fig. 1a and b). At first, in a non-teaching hospital, this lesion was interpreted as a suspected glioblastoma. At referral to our hospital, the lesion was diagnosed as being dural based, being most suggestive of dural metastasis with an unknown primary tumor. Additional screening revealed no other lesions or primary malignancy. Frameless navigation-guided biopsy of the lesion was performed. Initially, histopathological examination was aimed at diagnosing a malignancy, but did not show malignant cells. At second look, histopathological examination of the material revealed a rheumatoid nodule, with fibrinoid necrosis of granuloma-containing histiocytes. The diagnosis of focal rheumatoid pachymeningitis was made, and therapy was changed to another disease-modifying anti-rheumatic drug (DMARD) regimen in combination with glucocorticoids. Three months later, there was near-complete resolution of the lesion with disappearance of perifocal edema (Fig. 1c and d). A rheumatoid nodule is a characteristic extra-articular manifestation of rheumatoid arthritis. These nodules can occur intracranially as well. Case reports on intracranial rheumatoid involvement have been published before, but are rare (for a review, see [7]). There can be involvement of the pachymeninges (dura mater) as well as the leptomeninges (pia and arachnoid mater). The key MR finding in both conditions is meningeal enhancement [1–10]. A tumor-like presentation, as in our case, has not been published before. In the published case reports on intracranial rheumatoid nodules, two diagnostic methods were used. In some cases, the diagnosis was met by excluding other conditions that may cause meningeal enhancement such as infections (e.g., tuberculosis), tumors (e.g., lymphoma) and autoimmune disease (e.g., Behcet’s disease) by lumbar puncture and laboratory investigation. In most cases, as well as in ours, biopsy was performed. As biopsy leads to an accurate diagnosis and excludes a malignancy as differential diagnoses, we prefer this method. Because of the generally quick and good response to treatment, biopsy should be performed shortly K. Rijkers (*) :O. Schijns Department of Neurosurgery, Maastricht University Medical Center, PO BOX 5800, 6202 AZ Maastricht, The Netherlands e-mail: kimrijkers@gmail.com