Idiopathic hypertrophic cranial pachymeningitis presenting with headache.

Idiopathic hypertrophic cranial pachymeningitis is a rare inflammatory disease, usually involving the dura mater of skull base, tentorium, and falx. Chronic headache is the most common clinical manifestations. We report a case of idiopathic hypertrophic cranial pachymeningitis that was, initially, misdiagnosed as acute subdural hematoma along the tentorium cerebelli and posterior falx on the brain precontrast CT scan of a patient with severe headache. Correct diagnosis of pachymeningitis was made only after brain magnetic resonance imaging and meningeal biopsy.