Abstract text (incl. figure legends and references)

Question: Idiopathic Intracranial Hypertension (IIH) is a rare neurological disorder characterised by raised intracranial pressure (ICP). Severe cases can manifest with papilloedema and rapidly deteriorating vision. Reduction of ICP can be achieved through surgical procedures such as ventriculoperitoneal shunt (VPS) insertion. We aimed to establish detailed characteristics of patients with IIH who required surgical intervention. Secondly, we sought to describe their long-term recovery.

Methods: Data was collected prospectively at clinical visits. This included headache frequency, measures of papilloedema and ganglion cell layer volume (GCLV) on optical coherence tomography (OCT) imaging, perimetric mean deviation (MD) in people with IIH requiring VPS at a large regional neuroscience centre. Loess smoothers were used to characterise outcomes following surgery.

Results: 51 patients underwent VPS insertion (92% female [47/51], age 28.1 [SD 8.4], BMI 37.4 [SD 9.7], mean follow up 330 days [SD 290]). Characteristics of the worst eye at baseline included MD of -11.4 dB [SD 9.7], retinal nerve fibre layer thickness 381.9 µm [SD 116.6] and Frisen grade papilloedema 4.3 [SD 0.9].

Post-operatively, markers of papilloedema showed complete resolution by 4 months. Alarmingly, mean GCLV steadily declined from 1.05 µm3 at baseline to 0.95µm3 12 months post-operatively. Headache frequency fell from 12.7 days per month to 3.4 days at 3 month post-operatively, before increasing to 13.8 days by 12 months.

Conclusions: VPS insertion leads to a dramatic and sustained reduction in papilloedema by 4 months in IIH. However, macular ganglion cell layer loss continued at 12 months following surgery which may predispose to future sight loss. Whilst headache severity often improves following VPS, this is inconsistent and not sustained.