## Pathophysiology: Acute vs. Chronic Sinusitis **Key Point:** Chronic sinusitis is defined by symptom duration of ≥12 weeks with persistent mucosal inflammation and edema, even if symptoms fluctuate or improve with treatment. This is a temporal and histopathological definition, not merely a clinical one. ### Diagnostic Criteria Comparison | Feature | Acute Sinusitis | Chronic Sinusitis | | --- | --- | --- | | **Duration** | < 4 weeks | ≥ 12 weeks | | **Mucosal changes** | Reversible edema and inflammation | Persistent edema, remodeling, fibrosis | | **Fever/systemic symptoms** | Often present | Absent or mild | | **Purulent discharge** | Common | May or may not be present | | **Histology** | Acute inflammatory infiltrate | Chronic inflammatory infiltrate, metaplasia | | **Reversibility** | Resolves with treatment | May persist despite treatment | **High-Yield:** The American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) and European Position Paper on Rhinosinusitis (EPOS) define chronic sinusitis as symptoms lasting ≥12 weeks with objective evidence of inflammation (nasal endoscopy or CT imaging). **Mnemonic:** **CHRONIC = 12 weeks** (Chronic = 12 Weeks of inflammation) ### Pathophysiology of Chronicity Chronic sinusitis involves: 1. Persistent bacterial colonization or biofilm formation 2. Impaired mucociliary clearance (structural or functional) 3. Chronic inflammatory infiltration (lymphocytes, plasma cells, eosinophils) 4. Mucosal remodeling and fibrosis 5. Possible role of fungi, superantigens, or immune dysregulation **Clinical Pearl:** A patient with 10 weeks of symptoms does NOT yet have chronic sinusitis by definition, even if imaging shows sinus disease. The 12-week threshold is arbitrary but standardized for research and clinical practice consistency. [cite:EPOS 2020 Guidelines] 
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