A 35-year-old man with a history of chronic sinusitis presents with acute orbital cellulitis. Which paranasal sinus is the most common primary source of orbital cellulitis?

Question

Accepted Answer

D. Ethmoid sinus. ## Paranasal Sinus Sources of Orbital Cellulitis **Key Point:** The ethmoid sinus is the most common primary source of orbital cellulitis, accounting for 70–80% of cases. Its anatomical proximity to the orbit and thin lamina papyracea make it the most frequent route of spread. ### Anatomical Basis for Ethmoid Predominance | Sinus | Frequency | Anatomical Relationship to Orbit | |-------|-----------|----------------------------------| | **Ethmoid** | **70–80%** | Lateral wall of orbit; thin lamina papyracea; direct extension | | Maxillary | 10–15% | Inferior orbit; less direct communication | | Frontal | 5–10% | Superior orbit; less common source | | Sphenoid | <5% | Posterior orbit; rare source | **High-Yield:** The ethmoid sinus borders the medial orbit via the lamina papyracea (a thin bony plate). Infection readily breaches this barrier, making ethmoid sinusitis the leading cause of orbital cellulitis. ### Pathophysiology of Spread 1. **Acute ethmoiditis** → inflammation and infection of ethmoid air cells 2. **Lamina papyracea erosion or inflammation** → loss of anatomical barrier 3. **Direct extension** → pus and inflammatory cells enter the orbital space 4. **Orbital cellulitis** → proptosis, chemosis, ophthalmoplegia, vision loss ### Clinical Presentation Clues - **Medial proptosis** (not axial) suggests ethmoid source - **Medial orbital swelling** and chemosis - **Preceding upper respiratory infection** or acute sinusitis - **Fever, systemic toxicity** **Clinical Pearl:** A child with orbital cellulitis and recent rhinitis or upper respiratory infection should raise suspicion for ethmoid sinusitis as the primary source. Imaging (CT) will show air-fluid levels in the ethmoid sinus. ### Why Other Sinuses Are Less Common **Maxillary sinus:** - Located below the orbit; less direct anatomical communication - Accounts for only 10–15% of cases - More likely to cause periorbital cellulitis than true orbital cellulitis **Frontal sinus:** - Superior location; less frequent involvement - When involved, often in conjunction with ethmoid disease - Accounts for 5–10% of cases **Sphenoid sinus:** - Posterior and medial location; rare source (<5%) - When involved, may cause cavernous sinus thrombosis - Usually occurs with other sinus involvement **Mnemonic:** **EMFS** (Ethmoid > Maxillary > Frontal > Sphenoid) — order of frequency in orbital cellulitis. ### Imaging & Diagnosis - **CT orbits with contrast:** Shows air-fluid levels in ethmoid sinus, orbital edema, and abscess if present - **MRI:** Better for soft tissue delineation and cavernous sinus assessment - **Blood cultures:** Positive in 50% of cases - **Sinus aspirate culture:** Guides antibiotic therapy

Answer

A. Maxillary sinus

Answer

B. Sphenoid sinus

Answer

C. Frontal sinus

A 35-year-old man with a history of chronic sinusitis presents with acute orbital cellulitis. Which paranasal sinus is the most common primary source of orbital cellulitis?

Explanation

Paranasal Sinus Sources of Orbital Cellulitis

Anatomical Basis for Ethmoid Predominance

Pathophysiology of Spread

Clinical Presentation Clues

Why Other Sinuses Are Less Common

Imaging & Diagnosis

Practice similar questions

Join our NEET PG community

Sinus	Frequency	Anatomical Relationship to Orbit
Ethmoid	70–80%	Lateral wall of orbit; thin lamina papyracea; direct extension
Maxillary	10–15%	Inferior orbit; less direct communication
Frontal	5–10%	Superior orbit; less common source
Sphenoid	<5%	Posterior orbit; rare source