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Summary Table

Feature	Details
Risk Factors	Recent URI (most common), allergic rhinitis, nasal polyps, dental infections (maxillary), immunodeficiency, smoking, barotrauma, nasogastric/nasotracheal intubation, cystic fibrosis
Etiology	Viral (vast majority of acute cases); bacterial superinfection by Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis; fungal (Aspergillus, Mucor in immunocompromised)
Patient Presentation	Facial pain/pressure worsened by leaning forward, nasal congestion, purulent nasal discharge, anosmia/hyposmia, post-nasal drip, headache
Classic Physical Exam	Tenderness over the affected sinus on palpation, purulent discharge in the middle meatus on anterior rhinoscopy, transillumination showing opacity
Key Diagnostic Results	Clinical diagnosis in uncomplicated cases; CT sinus (gold standard imaging) showing mucosal thickening, air-fluid levels, or opacification
Management	Viral: symptomatic care (saline irrigation, decongestants, analgesics). Bacterial: amoxicillin-clavulanate first-line. Complicated/refractory: broader antibiotics, CT imaging, ENT referral
Keywords	"Symptoms >10 days without improvement," "double-worsening," "purulent discharge with facial pain," "air-fluid level on CT"

1. Pathophysiology

Rhinosinusitis begins with obstruction of the ostiomeatal complex (OMC), which is the final common pathway shared by the maxillary, anterior ethmoid, and frontal sinuses for mucociliary drainage. When the OMC is blocked, mucus accumulates within the sinus cavity, oxygen tension drops, and the local environment shifts from aerobic to anaerobic conditions. This creates an ideal medium for bacterial proliferation.

The most common precipitant is a viral upper respiratory infection, which causes mucosal edema and impairs ciliary function. The swollen mucosa physically narrows the ostia, trapping secretions. In roughly 0.5 to 2% of viral cases, secondary bacterial infection develops. The bacteria most commonly responsible are S. pneumoniae and H. influenzae, both of which thrive in the stagnant, oxygen-poor secretions. This is why patients develop purulent (thick, colored) discharge rather than the clear, watery rhinorrhea of a simple viral cold.

Facial pain and pressure localize to the affected sinus because the trapped secretions exert pressure on the sinus walls and surrounding periosteum. The pain classically worsens with leaning forward or Valsalva maneuver because these actions transiently increase venous pressure in the face and further distend the already pressurized cavity. Maxillary sinusitis causes cheek or upper dental pain, frontal sinusitis causes forehead pain, ethmoid sinusitis causes retro-orbital or periorbital pain, and sphenoid sinusitis causes vertex or occipital headache. This anatomic correlation is commonly tested.

In chronic rhinosinusitis (symptoms lasting 12 weeks or more), the pathophysiology shifts from acute infection toward persistent mucosal inflammation, tissue remodeling, and polyp formation. The epithelium undergoes squamous metaplasia, submucosal fibrosis develops, and the normal ciliated pseudostratified columnar epithelium loses its clearance function. This explains why chronic rhinosinusitis responds poorly to antibiotics alone and often requires intranasal corticosteroids and, in refractory cases, endoscopic sinus surgery to restore ventilation and drainage.

A special consideration is fungal rhinosinusitis. In immunocompromised patients (uncontrolled diabetes with ketoacidosis, neutropenia, organ transplant recipients), Mucor and Aspergillus can invade the sinus mucosa, causing invasive fungal sinusitis. This is an aggressive, tissue-destructive process with angioinvasion leading to black necrotic eschars on the nasal turbinates or palate. The pathophysiology here is direct vascular invasion and thrombosis by fungal hyphae. Recognizing this presentation in a vignette is critical because management is surgical debridement plus systemic antifungals, not antibiotics.

2. Classification and Clinical Manifestation

Classification	Duration	Key Clinical Features
Acute Viral Rhinosinusitis	< 10 days	Nasal congestion, clear to mucopurulent discharge, mild facial pressure, low-grade fever; symptoms improving by day 7 to 10
Acute Bacterial Rhinosinusitis (ABRS)	10 to 30 days (or double-worsening pattern)	Persistent symptoms beyond 10 days without improvement OR initial improvement followed by worsening ("double-worsening"); purulent nasal discharge, facial pain/pressure, fever > 39C with purulent discharge for 3 to 4 consecutive days (severe onset)
Subacute Rhinosinusitis	4 to 12 weeks	Persistent but less intense symptoms; represents incomplete resolution of acute episode
Chronic Rhinosinusitis (CRS)	> 12 weeks	Nasal obstruction, anterior/posterior mucopurulent drainage, facial pain/pressure, hyposmia; divided into CRS with nasal polyps and CRS without nasal polyps
Recurrent Acute Rhinosinusitis	4 or more episodes per year, each lasting 7 to 10 days, with complete resolution between episodes	Same presentation as ABRS but repeating pattern; raises suspicion for anatomic abnormality or allergic contribution
Acute Invasive Fungal Sinusitis	Rapid onset (days to weeks)	Immunocompromised host; black necrotic eschar on turbinate or palate, orbital symptoms (proptosis, vision loss), cranial nerve palsies; caused by Mucor (Rhizopus) or Aspergillus
Allergic Fungal Sinusitis	Chronic	Immunocompetent, atopic patient; unilateral nasal polyps, "peanut butter-like" thick allergic mucin, elevated IgE, eosinophilia; CT shows heterogeneous opacification with areas of high attenuation

The distinction between viral and bacterial acute rhinosinusitis is one of the most tested concepts. Three clinical criteria define ABRS:

Persistent symptoms lasting 10 days or more without improvement
Severe onset with high fever (above 39C) and purulent discharge for 3 to 4 consecutive days
Double-worsening: initial improvement of a viral URI followed by new onset of fever, headache, or increased nasal discharge

Any one of these three patterns is sufficient to diagnose ABRS clinically.

3. Diagnostic Workup

Test	Role	Key Findings
Clinical assessment	Best initial approach for uncomplicated ABRS	Meets criteria (persistent >10 days, severe onset, or double-worsening); no imaging needed
CT sinus (non-contrast)	Gold standard imaging; indicated for complicated, chronic, or refractory cases	Mucosal thickening > 4 mm, air-fluid levels, complete sinus opacification, bony erosion (suggests complication or tumor)
Nasal endoscopy	Adjunct in chronic or recurrent disease	Purulence from middle meatus, polyps, anatomic abnormalities (septal deviation, concha bullosa)
Sinus culture (endoscopic-guided)	Treatment failure after two courses of antibiotics	Identifies causative organism and antibiotic sensitivities
Plain radiograph (Waters view)	Largely replaced by CT; low sensitivity	Air-fluid level or complete opacification (limited diagnostic value)
MRI sinus	Suspected intracranial or orbital complication, or to differentiate tumor from retained secretions	Superior soft tissue contrast; distinguishes mucosal inflammation from neoplasm
Biopsy	Suspected fungal invasion or malignancy	Histopathology confirms invasive hyphae (broad non-septate for Mucor, narrow septate and 45-degree branching for Aspergillus)

Uncomplicated acute rhinosinusitis is a clinical diagnosis. This is a key testing point. The exam will not reward you for ordering a CT on a patient with a 12-day history of purulent nasal discharge and facial pressure who otherwise looks well. Imaging is unnecessary and inappropriate for a straightforward first episode of ABRS.

CT sinus without contrast becomes the study of choice when you suspect complications (periorbital cellulitis, orbital abscess, intracranial extension), when the patient fails to respond to appropriate antibiotic therapy, when evaluating chronic rhinosinusitis before surgical planning, or when the presentation is atypical. Air-fluid levels and complete opacification are the hallmark findings, but remember that CT cannot reliably distinguish viral from bacterial rhinosinusitis because mucosal changes are present in both. This is why clinical criteria, not imaging, drive the initial diagnosis.

Endoscopic sinus culture is reserved for patients who fail two courses of antibiotics. The culture must be obtained from the middle meatus under direct visualization (not a nasal swab, which reflects nasal flora and is unreliable). This distinction between an endoscopic culture and a simple nasal swab is testable.

For invasive fungal sinusitis, the workup is urgent. CT may show bony erosion and soft tissue invasion. However, the definitive diagnosis requires tissue biopsy showing fungal hyphae invading tissue, blood vessels, or bone. Do not wait for culture results in a diabetic ketoacidosis patient with a black eschar on the palate. The next best step is biopsy and urgent surgical consultation.

4. Management and Treatment

Scenario	Treatment	Details
Acute viral rhinosinusitis	Supportive care	Saline nasal irrigation, analgesics (acetaminophen/NSAIDs), topical decongestants (oxymetazoline) for no more than 3 days, oral decongestants (pseudoephedrine); no antibiotics
ABRS, first-line	Amoxicillin-clavulanate	875/125 mg PO twice daily OR high-dose 2 g/125 mg PO twice daily for 5 to 7 days (adults); high-dose preferred in areas with penicillin-resistant S. pneumoniae
ABRS, penicillin allergy	Doxycycline or respiratory fluoroquinolone (levofloxacin, moxifloxacin)	Doxycycline 100 mg PO twice daily for 5 to 7 days; levofloxacin 500 mg PO daily or moxifloxacin 400 mg PO daily for 5 to 7 days
ABRS, treatment failure (no improvement at 72 hours)	Switch to high-dose amoxicillin-clavulanate if not already used, or switch to respiratory fluoroquinolone	Reassess for complications; consider CT sinus
Chronic rhinosinusitis	Intranasal corticosteroids (first-line)	Fluticasone or mometasone daily for minimum 8 to 12 weeks; saline irrigation as adjunct; antibiotics only for acute exacerbations
CRS refractory to medical therapy	Functional endoscopic sinus surgery (FESS)	Restores OMC patency and sinus ventilation; continue intranasal steroids postoperatively
Invasive fungal sinusitis	Urgent surgical debridement + IV amphotericin B	Liposomal amphotericin B preferred for reduced nephrotoxicity; correct underlying immunosuppression (e.g., resolve DKA); voriconazole for Aspergillus
Allergic fungal sinusitis	Surgery + systemic corticosteroids	Endoscopic removal of allergic mucin and polyps; oral prednisone taper; intranasal steroids for maintenance

For acute viral rhinosinusitis, the single most important management principle is avoiding antibiotics. The exam commonly presents a patient with 5 to 7 days of nasal congestion, mild facial pressure, and clear-to-mucopurulent discharge, and the correct answer is symptomatic management only. Prescribing antibiotics here is a classic wrong answer. Topical decongestants like oxymetazoline should be limited to 3 days maximum to avoid rhinitis medicamentosa (rebound nasal congestion from chronic vasoconstrictor use).

For ABRS, the drug of choice is amoxicillin-clavulanate, not plain amoxicillin. Current guidelines from IDSA recommend amoxicillin-clavulanate over amoxicillin alone because of increasing beta-lactamase-producing H. influenzae and M. catarrhalis. The high-dose formulation (2 g/125 mg twice daily) is chosen in regions with high rates of penicillin-resistant pneumococcus, in patients with recent antibiotic use, or in patients who are immunocompromised. A treatment duration of 5 to 7 days is now considered sufficient for uncomplicated ABRS in adults, though some guidelines extend to 10 days.

If the patient has a penicillin allergy, the approach depends on the type of reaction. For non-anaphylactic allergy, doxycycline is preferred. For severe (type I hypersensitivity) allergy, a respiratory fluoroquinolone (levofloxacin or moxifloxacin) is appropriate. Macrolides (azithromycin, clarithromycin) are no longer recommended as monotherapy due to high rates of pneumococcal resistance.

Chronic rhinosinusitis is treated primarily with intranasal corticosteroids, not antibiotics. This is a frequently tested distinction. Saline nasal irrigation is an important adjunct. Antibiotics are reserved for acute exacerbations superimposed on the chronic baseline. When medical therapy fails after an adequate trial (typically 8 to 12 weeks), the next step is functional endoscopic sinus surgery (FESS) to widen the natural ostia and restore mucociliary drainage.

For invasive fungal sinusitis, the management is a surgical emergency. The next best step is always urgent surgical debridement combined with IV amphotericin B. Simultaneously, the underlying immunosuppression must be reversed (correct DKA, reduce immunosuppressive medications). Delay in surgery directly increases mortality.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Is Similar	Key Discriminator
Viral URI (common cold)	Nasal congestion, rhinorrhea, facial pressure, overlapping early symptoms	Viral URI improves by day 7 to 10; ABRS is diagnosed when symptoms persist beyond 10 days without improvement, or follow a double-worsening pattern
Allergic rhinitis	Nasal congestion, rhinorrhea, facial pressure, post-nasal drip	Allergic rhinitis features sneezing, watery (clear) discharge, itchy nose/eyes, bilateral pale/boggy turbinates; no purulent discharge, no fever; seasonal or perennial pattern
Migraine or tension headache	Facial pain, frontal headache, pressure sensation	Headache disorders lack purulent nasal discharge and nasal obstruction; migraine may have photophobia, nausea, aura; "sinus headache" is frequently misdiagnosed migraine
Dental abscess (periapical)	Unilateral maxillary pain, facial swelling, fever	Pain localizes to a specific tooth, worsened by percussion on that tooth; maxillary sinusitis from dental origin often shows unilateral disease with foul-smelling discharge; dental exam or panoramic radiograph clarifies
Nasal foreign body (pediatric)	Unilateral purulent, foul-smelling nasal discharge	Unilateral and foul-smelling discharge in a young child points toward foreign body rather than bilateral sinusitis; anterior rhinoscopy reveals the object
Wegener granulomatosis (GPA)	Chronic nasal crusting, purulent/bloody discharge, sinus destruction on imaging	Saddle nose deformity, c-ANCA/PR3 positive, pulmonary nodules, renal involvement (hematuria/proteinuria); multi-organ pattern distinguishes this from isolated sinusitis
Sinonasal malignancy (SCC, lymphoma)	Unilateral nasal obstruction, bloody discharge, facial pain	Unilateral symptoms, epistaxis, bony destruction on CT, cranial nerve deficits; older patient or occupational exposure (woodworking for adenocarcinoma); biopsy is diagnostic
Periorbital/orbital cellulitis	Complication of sinusitis, not a differential per se, but a progression the exam tests	Eyelid edema, proptosis, restricted extraocular movements, vision changes; CT shows ethmoid sinusitis with subperiosteal abscess; requires IV antibiotics and possibly surgical drainage

6. Traps and High-Yield Pearls

The most common way students lose points on rhinosinusitis questions is by prescribing antibiotics too early. A vignette describing 5 to 7 days of congestion, colored nasal discharge, and mild facial pain is almost certainly describing viral rhinosinusitis, and the correct answer is supportive care. The test-writer deliberately includes purulent discharge to tempt you into choosing antibiotics, but purulent discharge alone does not equal bacterial infection. You must apply the time-based criteria: persistent beyond 10 days, severe onset with high fever for 3 to 4 days, or double-worsening.

Another classic trap is ordering imaging for uncomplicated ABRS. The exam wants you to know that a first episode of clinically diagnosed bacterial sinusitis does not require a CT scan. Imaging is reserved for complications, treatment failure, or chronic disease evaluation.

Students also confuse the first-line antibiotic. The answer is amoxicillin-clavulanate, not plain amoxicillin and not azithromycin. Azithromycin as a sinusitis treatment is a distractor that appears frequently because it is commonly prescribed in practice, but it is no longer guideline-recommended due to pneumococcal resistance.

Finally, never miss the invasive fungal sinusitis vignette. A diabetic patient in ketoacidosis or a neutropenic patient with facial pain, black eschar on the palate or turbinate, and rapidly progressive orbital symptoms is mucormycosis until proven otherwise. The next best step is surgical debridement, not antibiotics and not a CT scan first. This is a surgical emergency, and delay kills.

The core competency being tested across rhinosinusitis questions is your ability to differentiate viral from bacterial disease using clinical criteria, to withhold antibiotics appropriately, to choose the correct first-line agent when antibiotics are indicated, and to recognize complications that escalate the workup and management.

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