A 28-year-old man is referred to the neuro-ophthalmology clinic with a 2-week history of progressive bilateral blurred vision and headaches. On examination, both optic discs are swollen with obscured margins, and the swelling is more pronounced at the superior and inferior poles. Visual acuity is preserved at 6/6 bilaterally. Fundoscopy shows no haemorrhages or exudates. Which investigation is most appropriate to differentiate papilloedema from bilateral papillitis and identify the underlying cause?

Explanation

## Investigation of Choice: Papilloedema vs Bilateral Papillitis ### Clinical Presentation Analysis The patient presents with: - **Bilateral optic disc swelling** with obscured margins - **Progressive course over 2 weeks** - **Preserved visual acuity** (6/6 bilaterally) - **Headaches** (suggesting raised intracranial pressure) - **No haemorrhages or exudates** (atypical for papillitis) This presentation is consistent with **papilloedema** (raised intracranial pressure) rather than bilateral papillitis, but the investigation must: 1. Confirm papilloedema 2. Identify the underlying cause of raised ICP 3. Exclude bilateral demyelinating optic neuritis ### Why MRI Brain with and without Contrast is the Investigation of Choice **Key Point:** MRI brain with and without contrast is the gold standard for investigating papilloedema because it identifies the underlying cause of raised intracranial pressure and excludes demyelinating disease. **High-Yield:** MRI brain findings in papilloedema include: - Enlarged blind spot - Flattening of the posterior globe - Optic nerve sheath distension (>6 mm) - Tonsillar herniation (if severe) - Identification of mass, hydrocephalus, venous sinus thrombosis, or idiopathic intracranial hypertension (IIH) ### Differential Diagnosis: Papilloedema vs Bilateral Papillitis | Feature | Papilloedema | Bilateral Papillitis | |---|---|---| | **Onset** | Gradual (weeks to months) | Acute to subacute (days to weeks) | | **Laterality** | Bilateral (symmetric) | Bilateral but often asymmetric | | **Pain** | Absent | Present (pain on eye movements) | | **Visual acuity** | Preserved until late | Early loss (central scotoma) | | **Headaches** | Present (due to raised ICP) | Absent | | **Haemorrhages/exudates** | Often present | Rare | | **MRI brain finding** | Structural cause of raised ICP | Normal or demyelinating lesions | | **Optic nerve sheath** | Distended (>6 mm) | Normal | **Clinical Pearl:** In this case, **preserved visual acuity with gradual bilateral disc swelling and headaches** strongly suggests papilloedema from raised ICP, not bilateral papillitis (which would present with acute vision loss and pain on eye movements). ### Why MRI is Superior to Other Investigations **Key Point:** MRI identifies the underlying cause of papilloedema, which is essential for management. ```mermaid flowchart TD A[Bilateral optic disc swelling]:::outcome --> B{Clinical features?}:::decision B -->|Gradual onset, preserved VA, headache| C[Suspect papilloedema]:::outcome B -->|Acute onset, vision loss, pain| D[Suspect papillitis]:::outcome C --> E[MRI brain with contrast]:::action E --> F{Findings?}:::decision F -->|Mass, hydrocephalus, venous thrombosis| G[Treat underlying cause]:::action F -->|Normal imaging + clinical criteria| H[Idiopathic intracranial hypertension]:::outcome D --> I[MRI brain + orbits]:::action I --> J[Detect demyelinating lesions]:::outcome ``` ### Comparison of Investigations | Investigation | Role | Limitation | |---|---|---| | **MRI brain ± contrast** | Gold standard; identifies cause of raised ICP; detects demyelination | — | | FFA | Shows optic nerve hyperfluorescence | Non-specific; does not identify underlying cause; no structural information | | OCT optic nerve head | Quantifies optic nerve swelling and axonal loss | Cannot identify cause of raised ICP; does not differentiate papilloedema from papillitis | | B-scan ultrasound | Measures optic nerve sheath diameter | Operator-dependent; does not identify underlying cause; poor soft-tissue contrast | **High-Yield:** In papilloedema, MRI must identify: - **Space-occupying lesion** (tumour, abscess) - **Hydrocephalus** (obstruction to CSF flow) - **Venous sinus thrombosis** (impaired venous drainage) - **Idiopathic intracranial hypertension** (IIH — diagnosis of exclusion) ### Clinical Pearls **Clinical Pearl:** The **absence of pain on eye movements** and **preserved visual acuity** in this patient make bilateral papillitis unlikely. Papillitis typically presents with acute vision loss and pain. **Warning:** Do not confuse papilloedema (raised ICP) with papillitis (inflammation of the optic nerve). The clinical presentation and MRI findings are distinctly different.