The effect of optic nerve sheath decompression on CSF dynamics in pseudotumour cerebri and related conditions

The effect of optic nerve sheath decompression (ONSD) on cerebrospinal fluid (CSF) pressure and outflow resistance was studied in six patients who underwent the procedure (four unilateral, two bilateral) for papilloedema secondary to raised intracranial pressure. Four patients (all female, average age 29.3 years) had pseudotumour cerebri while two patients (one male 34 years, one female 24 years) had cryptococcal meningitis. All patients had pre- and postoperative CSF pressure measurements. Three patients had a preoperative CSF infusion study and all six had a postoperative study to measure CSF outflow resistance. Five of the six patients had elevated CSF pressure prior to ONSD and in all five the pressure was still significantly elevated after the procedure. In one symptomatic patient with papilloedema the pressure was normal pre- and post-ONSD (this patient was on acetazolamide). All three patients who tested pre-ONSD had an abnormal outflow resistance; in only one case did this become normal after the procedure, although this patient later required shunting for persistent intracranial hypertension. Clinically, only one of the six cases had a substantial relief of symptoms and signs despite persistently high CSF pressure and outflow resistance. The other five patients went on to shunting after intervals ranging from one week to 8 months. The preliminary conclusion was drawn that ONSD does not have any predictable beneficial effect on CSF pressure or outflow resistance.