A 35-year-old man presents with acute onset proptosis, chemosis, ophthalmoplegia, and fever for 2 days. He has a history of acute rhinosinusitis. On examination, visual acuity is 6/9 with restricted eye movements. Which is the investigation of choice to confirm the diagnosis and guide management?

Explanation

## Investigation of Choice: Orbital Cellulitis ### Why CT Orbit and PNS with Contrast? **Key Point:** CT with IV contrast is the gold standard for diagnosis and management of orbital cellulitis because it: - Rapidly identifies the causative source (sinusitis, abscess, foreign body) - Delineates orbital involvement and extent of inflammation - Detects complications (subperiosteal abscess, cavernous sinus thrombosis) - Guides surgical intervention if needed - Fast acquisition (critical in acute presentation) ### Clinical Presentation Correlation This patient has the classic triad of orbital cellulitis: 1. **Proptosis** — forward displacement of globe 2. **Ophthalmoplegia** — extraocular muscle inflammation/edema 3. **Fever + systemic signs** — acute infection The **preceding rhinosinusitis** is the key clue — 70–80% of orbital cellulitis cases arise from paranasal sinusitis (especially ethmoid and maxillary), making imaging of both orbit AND sinuses essential. ### Why Contrast is Mandatory IV contrast enhancement: - Highlights inflamed orbital tissues - Differentiates cellulitis from abscess (abscess shows rim enhancement) - Visualizes vascular involvement (thrombosis risk) - Improves sensitivity for small abscesses **High-Yield:** Contrast-enhanced CT is superior to non-contrast CT for orbital pathology. ### Diagnostic Criteria on Imaging | Feature | Finding | |---------|----------| | **Orbital edema** | Increased density/signal in orbital fat | | **Sinus source** | Air-fluid level, mucosal thickening, opacification | | **Abscess** | Loculated collection with rim enhancement | | **Cavernous sinus involvement** | Abnormal enhancement, thrombosis | **Clinical Pearl:** In orbital cellulitis, imaging findings may lag behind clinical signs by 24–48 hours; do NOT delay treatment while awaiting imaging if clinical suspicion is high. ### Management Implications CT findings determine: - **Medical-only:** Cellulitis without abscess → IV antibiotics - **Surgical:** Subperiosteal/orbital abscess, foreign body → drainage + antibiotics - **Urgent intervention:** Cavernous sinus thrombosis → aggressive therapy [cite:Orbit & Oculoplasty, Essentials of Ophthalmology]