## Most Common Site of Acute Sinusitis **Key Point:** The maxillary sinus is the most frequently involved paranasal sinus in acute sinusitis, accounting for approximately 40–50% of cases. ### Anatomical and Pathophysiological Basis 1. **Ostial location and drainage**: The maxillary sinus ostium is located high on the medial wall (hiatus semilunaris), making gravity-dependent drainage difficult and predisposing to stasis. 2. **Dependent position**: Being the largest and most dependent sinus, secretions pool easily. 3. **Infection pathway**: Often follows upper respiratory tract infections (URTI) and dental infections. ### Frequency of Sinus Involvement (in descending order) | Sinus | Frequency | Clinical Features | |-------|-----------|-------------------| | Maxillary | 40–50% | Cheek pain, tooth pain, facial swelling | | Ethmoid | 30–40% | Medial canthal pain, periorbital edema | | Sphenoid | 5–10% | Vertex headache, retroorbital pain | | Frontal | 10–15% | Forehead pain, supraorbital tenderness | **Clinical Pearl:** Maxillary sinusitis often presents with dental pain (maxillary teeth) because the sinus floor is intimately related to tooth roots — this can mislead patients and clinicians into pursuing dental treatment first. **High-Yield:** In acute sinusitis, maxillary involvement is almost always present; it may occur in isolation or as part of pansinusitis. Ethmoid involvement is the second most common and often coexists with maxillary disease. **Mnemonic:** **MESF** (in order of frequency) — **M**axillary, **E**thmoid, **S**phenoid, **F**rontal. ### Why Maxillary Sinus Dominates - Largest sinus volume → greater surface area for infection - Ostium location (high on medial wall) → poor drainage - Proximity to dental roots → secondary infection from odontogenic sources - Most exposed to URTI pathogens via nasopharynx [cite:Scott-Brown's Otolaryngology Ch 5]
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