Sinusitis — Acute and Chronic

• Mucociliary clearance dysfunction (primary mechanism): The normal mucociliary clearance system requires intact ciliary function, appropriate mucus consistency, and patent ostia (sinus drainage pathways). Ciliary dysfunction may be primary (as in primary ciliary dyskinesia, an autosomal recessive disorder affecting dynein arm proteins and resulting in impaired mucociliary transport) or secondary (from viral injury, smoking, or pollution). When viral rhinosinusitis occurs, respiratory epithelial cells sustain direct injury from viral proteins and host inflammatory responses, leading to ciliary immotility lasting 3-4 weeks even after viral clearance. Mucus becomes thick and inspissated due to dehydration and inflammatory mediator accumulation. Ostial obstruction develops through mucosal edema (driven by mast cell degranulation and histamine/tryptase release) and polyp formation. The result is stasis of secretions within the sinus cavity, creating an oxygen-poor microenvironment that favors bacterial proliferation.

• Bacterial colonization and biofilm formation: When mucociliary clearance fails, pathogenic bacteria establish infection. Streptococcus pneumoniae, Haemophilus influenzae (nontypeable), and Moraxella catarrhalis are the classic pathogens in acute community-acquired sinusitis, though in acute disease, bacteria are often cultured as part of polymicrobial flora including anaerobes and commensals. In chronic sinusitis, the microbiology becomes more complex with increased prevalence of anaerobes (Peptostreptococcus, Prevotella), coagulase-negative staphylococci, and gram-negative organisms (Pseudomonas aeruginosa, particularly in patients with cystic fibrosis). Crucially, bacteria in the sinuses exist as biofilms—organized sessile communities embedded in an extracellular polysaccharide matrix that confers antibiotic resistance and reduced susceptibility to host immune factors. Biofilm-producing bacteria express reduced virulence factors and metabolic activity compared to planktonic bacteria, explaining why standard antimicrobial therapy is often insufficient in CRS. The biofilm matrix excludes antibiotics and limits penetration of immune cells.

• Persistent mucosal inflammation and immune dysregulation in chronic rhinosinusitis: In CRS, the pathophysiology shifts from acute bacterial infection toward chronic immune activation. This involves both innate and adaptive immune dysfunction: decreased numbers of dendritic cells, altered T helper (Th) cell balance (with phenotype varying by geography and eosinophil burden), and dysregulated IL-5 signaling in eosinophilic CRS subtypes. Type 2 inflammation predominates in some CRS phenotypes, driven by elevated IL-4 and IL-5 secretion, leading to increased infiltration by eosinophils and elevated IgE. Barrier dysfunction of the respiratory epithelium (disrupted tight junctions from reduced E-cadherin and claudin expression) allows increased paracellular bacterial antigen translocation. The epithelium itself becomes activated, producing antimicrobial peptides (lysozyme, lactoferrin) at reduced levels and adhesion molecules at elevated levels. Remodeling occurs with basement membrane thickening, excessive collagen deposition, and smooth muscle hyperplasia. Fungal antigens (from ubiquitous environmental fungi like Alternaria and Bipolaris) may serve as persistent immune triggers even when fungal infection is not active, contributing to chronic eosinophilic inflammation.

• Sinus ostial obstruction mechanisms: Beyond mucosal edema from acute inflammation, chronic obstruction may result from anatomic variants (septal deviation, uncinate process hypertrophy, paradoxical middle turbinate), polyp formation (benign sinonasal polyps filled with edematous, eosinophil-rich mucosa), or scarring from prior surgery or severe infection. The ostiomeatal complex (OMC)—comprising the maxillary ostium, anterior ethmoid cells, and middle turbinate—is the critical drainage pathway for the maxillary, anterior ethmoid, and frontal sinuses. Obstruction at this site is the anatomic bottleneck in most sinusitis cases.

• Inflammatory mediator cascade and tissue damage: Infection and mucosal injury trigger release of inflammatory cytokines (TNF-α, IL-6, IL-8), chemokines attracting neutrophils and eosinophils, and vasoactive mediators. These amplify mucosal edema, increase vascular permeability, and perpetuate epithelial damage. Neutrophilic elastase and reactive oxygen species released by activated immune cells can cause additional tissue injury. In allergic rhinitis (which predisposes to sinusitis), IgE-mediated mast cell activation releases histamine and tryptase, contributing to ostiomeatal complex edema and secondary bacterial sinusitis.

• Viral infection (primary trigger in acute sinusitis): Viral upper respiratory infections precede most cases of acute bacterial sinusitis. Common viruses include rhinovirus (most frequent), influenza, parainfluenza, adenovirus, respiratory syncytial virus (RSV), and coronavirus (including SARS-CoV-2). Viruses damage ciliated epithelium and trigger inflammatory edema of ostiomeatal complex structures, impair mucociliary clearance, and reduce local immune defenses, creating conditions for secondary bacterial infection. Viral rhinosinusitis alone typically resolves in 7-10 days; bacterial superinfection develops in approximately 2% of viral upper respiratory infections.

• Allergic rhinitis: Allergic rhinitis causes chronic OMC obstruction through IgE-mediated mast cell degranulation and eosinophilic inflammation. Approximately 50% of patients with CRS have concurrent allergic rhinitis. Allergic inflammation impairs sinus drainage and increases susceptibility to recurrent acute sinusitis, making allergen avoidance and intranasal corticosteroids (which reduce both allergic and non-allergic inflammation) important in management.

• Anatomic obstruction: Septal deviation, uncinate process pneumatization or hypertrophy, and concha bullosa (pneumatized middle turbinate) can narrow the OMC and impair drainage. Large septal deviation may cause contact point headaches or obstruct sinus ostia. These anatomic factors alone do not cause sinusitis but predispose to ostial blockade when concurrent mucosal edema occurs.

• Primary ciliary dyskinesia (PCD): This rare autosomal recessive condition involves inherited defects in ciliary structure (most commonly lacking dynein arms required for axonemal ATP hydrolysis and sliding motion). Patients present with chronic productive cough, recurrent sinusitis, otitis media with effusion, and bronchiectasis. Approximately 50% have situs inversus totalis (complete mirror-image reversal of thoracic and abdominal organs), a classic diagnostic clue. Diagnosis requires ciliary biopsy with transmission electron microscopy demonstrating structural defects and/or genetic testing.

• Cystic fibrosis (CF): CF mutations in the CFTR gene (cystic fibrosis transmembrane conductance regulator) impair chloride secretion, resulting in thick, dehydrated secretions and defective mucociliary clearance. Nearly 100% of CF patients develop CRS with nasal polyposis. Chronic Pseudomonas and Burkholderia infections are common. Sinus CT often shows opacification of all sinuses with polyps.

• Immunocompromise: Patients with HIV/AIDS, particularly those with CD4 <200 cells/μL, develop aggressive sinusitis with opportunistic pathogens (including fungal infections). Neutropenia, common variable immunodeficiency (CVID), and medications causing immunosuppression (corticosteroids, TNF-α inhibitors, chemotherapy) increase susceptibility.

• Fungal infection: Invasive fungal sinusitis occurs in immunocompromised hosts and presents with severe symptoms, tissue necrosis, and high mortality if untreated. Causative organisms include Aspergillus fumigatus, Mucor species (especially in diabetics with diabetic ketoacidosis), and Candida. Fungal ball (aspergilloma) represents colonization of the sinus by Aspergillus without tissue invasion; it often presents incidentally on imaging or with minimal symptoms. Allergic fungal sinusitis (AFS) is a non-invasive entity characterized by hypersensitivity reaction to fungal antigens, resulting in eosinophil-rich inflammation and thick, tenacious secretions; it occurs in immunocompetent individuals and is associated with asthma and atopic disease.

• Smoking and environmental pollutants: Active smoking impairs ciliary function and mucociliary clearance within days, significantly increasing risk of sinusitis and prolonging symptom duration. Secondhand smoke exposure has similar effects in children.

• Gastroesophageal reflux disease (GERD): Refluxed acid damages respiratory epithelium and impairs mucociliary clearance, predisposing to sinusitis. Conversely, sinusitis may worsen reflux through swallowing of infected secretions and increased cough reflex.

• Nasal polyps: Benign polyps obstruct the OMC and impair drainage. While polyps are present in only ~5% of the general population, they occur in 30-50% of CRS patients and in nearly all CF patients. Polyp presence is associated with more severe CRS and higher revision surgery rates.

• Dental pathology: Odontogenic infections, root canals, and dental extractions can spread to the maxillary sinus, which shares an anatomic boundary with the maxillary teeth. Maxillary sinusitis may be odontogenic in origin (~10% of cases).

• Recent nasal surgery or trauma: Instrumentation or septal surgery can disrupt anatomy, create adhesions, or lead to scarring that obstructs drainage pathways.

• Asthma and eosinophilic diseases: Asthma is present in 40-60% of CRS patients, and CRS is associated with asthma exacerbations. Chronic eosinophilic rhinosinusitis (characterized by tissue eosinophilia >10 eosinophils per high-power field) represents a distinct CRS phenotype and is associated with nasal polyps, elevated serum IgE, and poor response to standard therapy.

Acute sinusitis

• Purulent nasal discharge and congestion: Nasal obstruction results from mucosal edema and inflammatory cell infiltration. Purulent (yellow-green) drainage suggests bacterial infection, though color alone does not reliably predict bacterial versus viral etiology. Patients describe posterior drainage of purulent secretions, which may irritate the pharynx.

• Facial pain and pressure sensation: Pain typically localizes over the affected sinuses—maxillary sinusitis causes cheek and upper tooth pain, frontal sinusitis causes pain over the forehead, and ethmoid sinusitis causes pain between the eyes (can be confused with tension headaches). Pain is often worse when bending forward or in the morning (from gravity and positional pressure changes) and may be bilateral. The underlying mechanism involves inflammatory mediator stimulation of trigeminal nerve (CN V) pain fibers in the sinus mucosa. Pain severity helps distinguish bacterial (typically moderate-to-severe) from viral (mild-to-moderate) rhinosinusitis.

• Hyposmia or anosmia: Loss of smell results from nasal obstruction preventing odorant molecules from reaching olfactory epithelium in the superior nasal cavity and from inflammatory damage to olfactory receptor neurons. This may persist for weeks after infection.

• Cough and throat clearing: Postnasal drip from infected secretions irritates the pharynx and stimulates the cough reflex. Cough is often worse at night when supine (gravity promotes posterior drainage).

• Constitutional symptoms: Low-grade fever, malaise, and fatigue occur more commonly in acute bacterial sinusitis than viral disease. High fever should raise concern for complications (orbital cellulitis, meningitis, or brain abscess).

• Symptoms NOT typically caused by sinusitis: Dizziness, vertigo, hearing loss, and tinnitus are not directly caused by uncomplicated sinusitis and suggest alternative diagnoses (inner ear disease, eustachian tube dysfunction, or a complication like labyrinthitis).

Chronic rhinosinusitis (CRS)

• Chronic nasal obstruction and drainage: Unlike acute disease, purulence is not required for diagnosis. Symptoms must persist ≥12 weeks. Drainage may be clear, mucoid, or purulent. Obstruction is often bilateral and progressive, significantly impacting quality of life and sleep.

• Chronic or recurrent facial pain: Pain may be less severe than in acute sinusitis but is persistent and demoralizing. Some patients develop medication overuse headache from excessive analgesic use.

• Recurrent acute exacerbations: CRS is punctuated by acute episodes of increased purulence, pain, and fever superimposed on chronic baseline symptoms.

• Reduced quality of life: CRS patients report impaired sleep quality, daytime somnolence, reduced cognitive function, and work productivity loss comparable to that of patients with COPD or angina.

• Nasal polyps (in subset of patients): Polyps appear as smooth, pale, edematous masses obstructing the nasal cavity. They are non-tender and insensate, distinguishing them from other masses. Polyp presence indicates more severe disease and predicts worse outcomes.

Physical examination findings

• Nasal endoscopy (gold standard exam for sinusitis): Direct visualization with rigid or flexible endoscopes allows direct assessment of drainage site, polyps, and mucosal quality. Findings include mucopurulent drainage from the OMC, nasal polyps, mucosal edema, erythema, crusting, or granulation tissue. Endoscopy identifies the specific sinus(es) affected and drainage characteristics, guiding treatment. In acute disease, purulent drainage specifically from the OMC is the most specific finding for bacterial sinusitis.

• Facial tenderness and percussion tenderness: Gentle percussion over the maxillary sinuses (over the cheek) or frontal sinuses (forehead) may elicit tenderness in acute bacterial sinusitis. However, tenderness is nonspecific and insensitive and should not drive diagnosis.

• Fever: Low-grade fever may accompany acute bacterial sinusitis. High fever (>38.5°C) warrants concern for complications.

• Proptosis, chemosis, ophthalmoplegia: These signs indicate orbital involvement and are medical emergencies (see Complications).

Clinical diagnosis of acute bacterial sinusitis (ACS)

• Major factors (any one suggests ACS when associated with nasal symptoms):
• Purulent nasal drainage (thick, yellow-green secretions seen on exam or reported by patient)
• Nasal obstruction
• Facial pain, pressure, or fullness
• Hyposmia or anosmia
• Fever (temperature >38.5°C)

• Diagnosis criteria: ACS is diagnosed when symptoms persist for ≥10 consecutive days or when acute worsening (new fever, nasal drainage, or facial pain) occurs after 5-6 days of initial improvement ("double sickening"). A patient with 10+ days of symptoms and purulent nasal drainage on exam, especially with facial pain and fever, has a high pretest probability of bacterial ACS. The

Uncomplicated acute bacterial rhinosinusitis (ABRS)

• Watchful waiting: the AAO-HNS adult sinusitis guideline permits either 7 days of observation with symptomatic care or immediate antibiotics in reliable patients, because most ABRS resolves spontaneously.
• Symptomatic therapy: analgesics, high-volume saline irrigation, and an intranasal corticosteroid (e.g., fluticasone) to reduce ostiomeatal edema and restore drainage.
• First-line antibiotic: aminopenicillin — amoxicillin or amoxicillin-clavulanate. IDSA favors amoxicillin-clavulanate outright to cover beta-lactamase–producing H. influenzae and M. catarrhalis; AAP recommends amoxicillin (± clavulanate) in children.
• Penicillin allergy: doxycycline, or a respiratory fluoroquinolone (levofloxacin) reserved for those without alternatives given FDA boxed warnings. Cephalosporin cross-reactivity is only about 1–3% and is driven by shared R1 side chains, so a third-generation cephalosporin plus clindamycin is acceptable in non-anaphylactic allergy.
• Failure at ~7 days: reassess diagnosis, then escalate to high-dose amoxicillin-clavulanate or change class; obtain endoscopically guided culture rather than empirically cycling antibiotics.

Orbital (Chandler spectrum) — emergencies once postseptal

• Preseptal cellulitis: lid edema and erythema with normal extraocular movement, vision, and no proptosis; managed with antibiotics alone.
• Orbital (postseptal) cellulitis and subperiosteal abscess: ethmoid infection crosses the lamina papyracea — the classic pediatric route. Signalled by proptosis, painful/limited extraocular movement, chemosis, diplopia. Vision loss or a relative afferent pupillary defect means optic nerve compromise: contrast CT, IV antibiotics, and surgical drainage without delay.
• Cavernous sinus thrombosis: retrograde spread via ophthalmic veins. Bilateral ophthalmoplegia (CN VI palsy first, as it lies free in the sinus), V1/V2 sensory loss, and rapid deterioration. Emergency.

Intracranial — all emergencies

• Meningitis, epidural/subdural empyema, brain abscess: frontal or sphenoid disease seeding the frontal lobe; headache with fever, focal deficit, seizure, or personality change is the tip-off. Subdural empyema deteriorates fastest.
• Pott puffy tumor: frontal bone osteomyelitis with subperiosteal abscess — a doughy, boggy forehead swelling; implies underlying intracranial extension until imaging proves otherwise.

Treatment-related

• Antibiotics: Clostridioides difficile colitis, amoxicillin-induced morbilliform rash if the "sinusitis" is actually EBV pharyngitis, fluoroquinolone tendinopathy/aortopathy.
• Endoscopic sinus surgery: cribriform plate breach → CSF rhinorrhea and meningitis risk; lamina papyracea breach → orbital hematoma or diplopia; sphenopalatine or anterior ethmoidal artery injury → epistaxis; synechiae with restenosis.
• Amphotericin B: nephrotoxicity, hypokalemia, hypomagnesemia.

• The two clinical triggers for antibiotics: symptoms ≥10 days without improvement, OR double sickening (worsening after initial improvement). Severe symptoms with high fever and purulence for 3–4 consecutive days also qualifies under IDSA. Anything shorter is viral and gets supportive care only.
• First-line drug: amoxicillin-clavulanate (IDSA) or amoxicillin ± clavulanate (AAO-HNS). The classic triad of organisms is S. pneumoniae, nontypeable H. influenzae, and M. catarrhalis — the latter two make beta-lactamase, which is why clavulanate is added.
• Imaging is not part of diagnosing uncomplicated sinusitis. Order contrast CT (or MRI for intracranial/cavernous sinus questions) only when orbital or intracranial complication is suspected. Air-fluid levels and mucosal thickening occur in plain viral colds and cannot distinguish viral from bacterial disease — the single most common distractor.
• Ethmoid sinusitis is the usual source of orbital cellulitis in children, spreading through the lamina papyracea. Pain with eye movement plus proptosis = postseptal until proven otherwise; preseptal cellulitis spares motility and vision.
• Diabetic in DKA with facial pain and a black eschar on the turbinate or hard palate = mucormycosis. Best next step is urgent surgical debridement with liposomal amphotericin B, not a CT-then-wait strategy.
• Nasal polyps in a child should prompt sweat chloride/CFTR testing for cystic fibrosis. Polyps plus asthma plus aspirin sensitivity in an adult is Samter's triad (aspirin-exacerbated respiratory disease).
• Recurrent sinusitis + otitis + bronchiectasis + situs inversus = Kartagener syndrome (primary ciliary dyskinesia, dynein arm defect).
• Oxymetazoline beyond 3 days causes rebound congestion (rhinitis medicamentosa) — a favorite stem for "congestion that got worse on treatment."
• Penicillin allergy pitfall: cross-reactivity with cephalosporins is roughly 1–3% and side-chain driven; doxycycline is the standard non–beta-lactam alternative. Macrolides and TMP-SMX are no longer recommended because of pneumococcal resistance.