Which paranasal sinus is most frequently implicated as the source of orbital cellulitis?

Explanation

## Paranasal Sinus Origin in Orbital Cellulitis **Key Point:** The ethmoid sinus is the most common source of orbital cellulitis, accounting for 50–80% of cases. This is due to its anatomical proximity to the orbit and the thinness of the lamina papyracea, which separates the ethmoid air cells from the medial orbital wall. ### Anatomical Basis **High-Yield:** The lamina papyracea is a paper-thin bony partition between the ethmoid sinus and the medial orbit. Infection readily crosses this barrier, making ethmoiditis the primary risk factor for orbital cellulitis. ### Frequency of Sinus Involvement | Sinus | Frequency as Source | Anatomical Reason | | --- | --- | --- | | Ethmoid | 50–80% | Lamina papyracea is thin; direct medial wall contact | | Maxillary | 10–20% | Inferior orbital wall involvement; less direct | | Sphenoid | 5–10% | Posterior orbit; less common; associated with cavernous sinus thrombosis | | Frontal | 5–10% | Superior orbital wall; rare as sole source | | Multiple sinuses | 10–15% | Pansinusitis increases risk | **Clinical Pearl:** Ethmoid sinusitis in children is particularly dangerous because the lamina papyracea is even thinner and more porous in the pediatric population, allowing rapid spread of infection into the orbit. ### Pathophysiology 1. **Acute sinusitis** (viral or bacterial) → mucosal edema and impaired drainage 2. **Osteitis** of the lamina papyracea → bone resorption 3. **Direct breakthrough** into the orbital space 4. **Abscess formation** (subperiosteal or intraorbital) 5. **Orbital cellulitis** with proptosis, ophthalmoplegia, and visual compromise **Mnemonic:** **EMOS** — **E**thmoid (most common), **M**axillary (second), **O**ther sinuses (sphenoid/frontal rare), **S**pread (hematogenous, rare).