MRI of the brain disclosed abnormal linear dural enhancement and T2 hyperintensity of dura mater, including falx and tentorium (figure 1).

On clinical and MRI grounds, hypertrophic cranial pachymeningitis (HCP) was diagnosed, and idiopathic HCP was ascertained after second-line investigations failed to ascertain a known aetiology: serological tests to syphilis and Lyme disease were negative; all cerebrospinal fluid stains and cultures to fungi and Mycobacterium tuberculosis were negative; chest CT was normal; c-ANCA were negative; minor salivary glands biopsy was normal; biopsy of the right superficial temporal artery revealed no arteritis. Leptomeningeal biopsy showed infiltrates of mature lymphocytes, without evidence of granuloma, vasculitis or neoplastic cells.

HCP is a rare disorder due to local or diffuse inflammation of the dura mater with abnormal dural enhancement revealed on MRI.¹ Aetiological diagnosis of HCP is still a challenge. Once intracranial hypotension is ruled out on the basis of clinical features – orthostatic headache – four conditions should be evoked: (1) infectious diseases, mainly tuberculosis,² syphilis, HTLV1, Lyme disease and fungal infections; (2) neoplasia, mainly lymphoma³ and dural carcinomatosis; (3) granulomatous diseases such as neurosarcoidosis or Wegener's disease⁴; (4) vasculitis, either primary⁵ or secondary to rheumatoid arthritis or temporal arteritis.