A 19-year-old woman presented with a 10-day history of continuous headache, mild photophobia and nausea; her medical and recent travel history were unremarkable as was the clinical examination. Cerebrospinal fluid (CSF) analysis (120 cells/microl; 85% lymphocytic and 15% monocytic cells; protein 1,031.6 mg/l; glucose and lactate within the normal range) was consistent with aseptic meningitis. Treatment with acyclovir was given until proof of negative CSF PCR for herpes simplex virus. One week after admission, the patient's condition worsened with a decline in cognitive functions and a generalized epileptic seizure. She was started on levetiracetam. A prominent sulcal and leptomeningeal enhancement was noted on FLAIR MRI after contrast involving both hemispheres and the cerebellum in the absence of focal parenchymal lesions. T1-weighted postcontrast MRI also showed a slight leptomeningeal enhancement (fig. 1). Repetitive broad serologic examinations (Herpesviridae, HIV, enterovirus, adenovirus, respiratory syncytial virus, measles, mumps, rubella, Tick-borne encephalitis virus, influenza, borreliosis, leptospirosis, Chlamydia pneumoniae and trachomatis, Listeria monocytogenes, Legionella pneumophila, Mycobacterium tuberculosis, Treponema pallidum, Mycoplasma pneumoniae, Bartonella henselae and Haemophilus influenzae) and viral full-genome sequencing could not identify a pathogen. In the absence of any eosinophilia, a fungal or parasitic etiology was unlikely, neither was there any hint at a systemic autoimmune disease. The patient complained about a progressive headache intensity with continuous nausea and repeated vomiting (an overview of the clinical course is given in fig. 2). Repeated MRI demonstrated an increasing severity of the leptomeningeal contrast enhancement. A CSF opening pressure of >60 cm H2O was documented. In the further course, she developed a right sixth nerve palsy and metamorphopsia due to bilateral papilledema. Follow-up MRI demonstrated prominent optical nerves and an empty sella compatible with intracranial hypertension; venous thrombosis was ruled out. At this time, transcranial Dopp-ler indicated vasospasms of the middle cerebral artery, which gradually resolved on nimodipine. In repetitive lumbar punctures, an opening pressure of >60 cm H2O was measured; after drainage of 30 ml CSF and under oral therapy with acetazolamide, a rapid but short-lasting symptom improvement was achieved after each lumbar puncture. Over the course of 14 days, a maximum CSF cell count of 314/microl and a protein level >2,000 mg/l were found. CSF glucose and lactate were always within the normal range. Cytology varied between 80 and 97% of lymphocytes and between 3 and 20% of monocytes in the CSF. Increased blood-brain barrier (BBB) permeability was repeatedly demonstrated as illustrated in the Reibergram (fig. 3). We decided to place a temporary external lumbar drainage to reduce intracranial pressure (ICP) and to avoid further punctures. Subsequently, the patient became gradually headache free, and the sixth nerve palsy and the visual disturbances gradually resolved. After 7 days, the drain was removed, and another 10 days later, the patient was discharged and fully recovered over the course of the following 4 weeks. A follow-up CSF analysis including opening pressure and MRI findings returned to normal.