A 7-year-old boy presents with fever, left eye swelling, and proptosis for 2 days. On examination, the left eye shows chemosis, lid edema, and ophthalmoplegia (restricted upward and medial gaze). Fundoscopy reveals disc edema. CT orbit shows inflammatory changes in the left ethmoid sinus with orbital fat stranding. Blood culture is pending. Which organism is most likely responsible, and what is the immediate next step in management?

Explanation

## Clinical Diagnosis **Key Point:** Orbital cellulitis in a child with ethmoid sinusitis is a surgical emergency requiring broad-spectrum antibiotics and source control. ### Organism Identification The patient presents with classic orbital cellulitis secondary to acute ethmoid sinusitis. In pediatric cases, the most common causative organisms are: | Organism | Frequency | Risk Factor | | --- | --- | --- | | *Staphylococcus aureus* | 40–50% | Most common; can be MRSA | | *Streptococcus pneumoniae* | 20–30% | Sinusitis, post-vaccination decline | | *Haemophilus influenzae* type b | <5% | Rare post-Hib vaccine | | *Anaerobes* (Peptostreptococcus) | 10–15% | Dental/periodontal source | **Clinical Pearl:** The presence of ophthalmoplegia and disc edema indicates severe orbital inflammation with risk of vision loss and cavernous sinus thrombosis. This is NOT simple preseptal cellulitis. ### Management Algorithm ```mermaid flowchart TD A[Orbital cellulitis + sinusitis]:::outcome --> B{Imaging findings?}:::decision B -->|Abscess/pus collection| C[IV broad-spectrum antibiotics]:::action C --> D[Urgent ENT consultation for drainage]:::action B -->|Inflammatory edema only| E[IV antibiotics alone]:::action C --> F[Monitor vision, IOP, pupil reactivity]:::action D --> G[Endoscopic sinus drainage if no improvement in 48 hrs]:::action G --> H[Reassess imaging, culture results]:::outcome ``` ### Antibiotic Regimen **High-Yield:** Empiric therapy must cover *S. aureus* (including MRSA) and gram-negative organisms pending culture: 1. **First-line:** IV ceftriaxone 2 g BD + IV vancomycin 15–20 mg/kg/dose 6-hourly 2. **Alternative:** IV cefotaxime + vancomycin (if cephalosporin allergy: fluoroquinolone + vancomycin) 3. **Duration:** Minimum 2–3 weeks IV; switch to oral after clinical improvement and culture sensitivities ### Surgical Drainage Indications **Warning:** Do NOT delay surgery if: - Abscess on imaging (>1 cm) - No improvement after 48 hours of antibiotics - Deteriorating vision or afferent pupil defect - Proptosis worsening Endoscopic sinus drainage (via ethmoidotomy) is the standard approach in pediatric cases. ### Monitoring Parameters - Visual acuity and color vision daily - Pupil reactivity and extraocular motility - Intraocular pressure (risk of secondary glaucoma) - Blood culture results (guide antibiotic de-escalation) - Repeat imaging at 48–72 hours if not improving **Mnemonic:** **ABCDE of orbital cellulitis management** - **A**ntibiotics (broad-spectrum, IV) - **B**lood cultures before antibiotics - **C**T/MRI for imaging - **D**rainage if abscess or no improvement - **E**NS involvement (always check sinuses) [cite:Kanski Clinical Ophthalmology 9e Ch 6]