Sinusitis

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Sinusitis

Sinusitis (rhinosinusitis) is inflammation of the paranasal sinuses. It is one of the most common diagnoses in outpatient medicine and a leading driver of unnecessary antibiotic prescribing.

Definition and Classification

Sinus symptoms are classified by duration:

Category	Duration
Acute	< 4 weeks
Subacute	4-12 weeks
Chronic	≥ 12 weeks
Recurrent acute	≥ 4 episodes/year without symptoms between episodes

Harrison's Principles of Internal Medicine 22E, p.299

Etiology and Pathophysiology

Acute sinusitis is caused primarily by respiratory viruses. Although bacteria cause fewer than 2% of sinusitis episodes (most often S. pneumoniae, H. influenzae, or M. catarrhalis), antibiotics are prescribed at over 70% of office visits. According to guideline criteria, probably no more than 20-50% of adults meet antibiotic prescribing criteria.

Pathophysiologically, most cases are preceded by rhinitis, which produces mucosal edema that impairs sinus drainage. Maxillary sinusitis can also arise by extension of a periapical dental infection through the bony sinus floor. Outflow obstruction occurs most often in the frontal and anterior ethmoid sinuses and may cause mucus accumulation (mucocele).

Chronic sinusitis is typically polymicrobial, largely composed of normal oral microbes. Staphylococcus aureus, anaerobes, and fungi become more prominent. Fungi may cause severe chronic sinusitis especially in diabetic patients (e.g., mucormycosis). Sinusitis also occurs as a component of Kartagener syndrome (bronchiectasis + situs inversus + sinusitis) due to inherited ciliary defects.

Robbins, Cotran & Kumar Pathologic Basis of Disease, p.803-805
Harrison's 22E, p.299

Clinical Features

Symptoms:

Purulent nasal discharge
Facial congestion, fullness, or pressure/pain
Postnasal drip, halitosis, cough, fatigue
Fever, hyposmia or anosmia
Ear pressure/fullness
Maxillary toothache

Risk factors: Age 45-65, smoking, asthma, air travel, allergies.

Exam findings: Direct rhinoscopy shows excess mucus or purulence. Tenderness over maxillary sinuses; in severe cases, erythema and swelling. Sinus transillumination is not accurate for diagnosis.

Harrison's 22E, p.299

Differential Diagnosis

Common cold / allergic rhinitis
Vasomotor rhinitis
Rhinitis medicamentosa (from topical decongestants)
Drug-induced rhinitis (aspirin, NSAIDs, beta-blockers)
Granulomatosis with polyangiitis
CSF leak
Dental pathology / temporomandibular disorder
Headache syndromes
Invasive fungal infection (especially in immunocompromised)
Foreign body (especially in children)

Antibiotic Prescribing Criteria

Antibiotics should only be prescribed when symptoms meet one of these criteria (Harrison's Table 37-2):

Indication	Definition
Persistent	Symptoms lasting ≥ 10 days
Severe	Fever > 102°F AND purulent nasal discharge or facial pain for ≥ 3-4 consecutive days
Worsening	New fever, headache, or increased nasal discharge following an upper respiratory infection that lasted 5-6 days and was initially improving ("double sickening")

Harrison's 22E, p.299-300

Treatment

Symptomatic (all patients)

Intranasal decongestants: oxymetazoline, 2 sprays each nostril BID, for no more than 5 days
Oral decongestants: pseudoephedrine 120 mg extended-release during the day
Analgesics/antipyretics: acetaminophen or ibuprofen
Nasal saline spray or washes
Intranasal glucocorticoids - particularly helpful with an allergic component

Antibiotic Therapy (when criteria met)

First line: Amoxicillin/clavulanate 875/125 mg PO BID x 7 days. Amoxicillin 875 mg PO BID x 7 days is an acceptable alternative.

Penicillin allergy (mild): Cefuroxime

Penicillin allergy (severe): Doxycycline

Not recommended: Macrolides (high rates of macrolide-resistant S. pneumoniae)

No improvement after 3-5 days on first-line antibiotic:

Amoxicillin/clavulanate 2000/125 mg PO BID x 7 days, OR
Levofloxacin (note: fluoroquinolones carry risks of dysglycemia, neuropathy, tendon and aortic rupture)

Still no improvement after second-line antibiotic: Refer to otorhinolaryngology and/or obtain non-contrast CT.

Chronic Sinusitis

Medical treatment with antibiotics for 4-6 weeks
Nasal saline irrigation (recent meta-analysis supports budesonide nasal irrigation for chronic rhinosinusitis)
Adenoidectomy may help in younger children
Endoscopic sinus surgery (FESS) for failed medical management, targeting involved sinuses
Harrison's 22E, p.299-300
K.J. Lee's Essential Otolaryngology, p.1015

Complicated Sinusitis

Frontal and ethmoidal sinusitis usually responds to decongestants and antibiotics. Failure to respond or evidence of spread beyond the sinus requires drainage. Failure to recognize extra-sinus spread can lead to orbital abscess and intracranial infection - this should be identified within 24 hours of the first signs.

If infection spreads beyond the frontal sinus (bony wall infection + venous thrombosis through bone), prolonged antibiotics are required - 8-12 weeks. A patient may show dramatic initial improvement with a 2-week course, creating a false sense of security - this is a pitfall; stopping short risks chronic osteomyelitis or secondary intracranial sepsis.

Complications include:

Orbital cellulitis and abscess
Osteomyelitis
Meningitis
Intracranial abscesses
Cavernous sinus thrombosis
Septic thrombophlebitis of dural venous sinuses

Red flags requiring urgent reassessment: confusion, unilateral weakness, proptosis, limited ocular movements, acute vision changes.

Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol 1, p.495
Harrison's 22E, p.299

Fungal Sinusitis

Classification

Invasive:

Acute invasive fungal sinusitis (AIFS) - occurs in immunocompromised patients; rapidly progressive and potentially fatal. CT may show subtle bone erosion; early finding is severe unilateral nasal mucosal inflammatory changes. MRI is superior (sensitivity 85% vs CT 63%) - look for "black turbinate sign" (non-enhancing devitalized tissue on post-contrast MRI), obliteration of periorbital fat, leptomeningeal enhancement.
Chronic invasive fungal sinusitis (CIFS) - immunocompetent or mildly immunocompromised (e.g., diabetics). Homogeneous opacification without focal hyperdensities; limited unilateral bony erosion.
Chronic granulomatous invasive fungal sinusitis (CGIFS) - seen mainly in Africa/South Asia; usually Aspergillus spp; immunocompetent individuals.

Non-invasive:

Allergic fungal sinusitis (AFS) - immunocompetent atopic patients; "allergic mucin" visible on endoscopy. CT: bilateral multisinusal opacification with sinus expansion, bony erosion, and intra-sinus high attenuation (calcium, heavy metals, inspissated secretions).

Causative Organisms

Mucorales fungi (mucormycosis) - especially in uncontrolled diabetes
Aspergillus spp. (A. flavus has high propensity for acute sinus infection; cavernous sinus thrombosis involving CN III, IV, V, VI)

Management of AIFS

This is a diagnostic and therapeutic emergency
Nasal endoscopy + biopsy (frozen section to accelerate treatment)
Gadolinium-enhanced MRI is the preferred imaging modality
Wide debridement to viable tissue
IV antifungal agents
Surgical debridement often required
Treat even without histologic confirmation of invasion if clinical scenario + fungal elements on silver stain or culture are consistent

CT and MRI of Aspergillus sinusitis (Cummings Otolaryngology):

CT (A) shows left maxillary sinusitis with bony wall erosion; T2 MRI (B) shows thickened mucosa with hypointense signal at bony destruction site

Fig: (A) Coronal CT - left maxillary sinusitis with erosion of the superior lateral bony wall. (B) T2 axial MRI - thickened left maxillary sinus mucosa with hyperintense inflammation and a hypointense signal corresponding to bone destruction. Differential includes invasive fungal disease, lymphoma, and SCC.

Cummings Otolaryngology Head and Neck Surgery, p.231-233
Scott-Brown's Otorhinolaryngology Head & Neck Surgery Vol 1

Nosocomial Sinusitis

Occurs in critically ill patients, particularly those with nasotracheal intubation. Management: address precipitating factors (e.g., remove nasal tube) and treat empirically with broad-spectrum antibiotics until culture/sensitivity results are available.

Special Populations

Immunocompromised Patients

Initial evaluation includes thorough head and neck exam, nasal endoscopy, and endoscopy-guided cultures from the middle meatus or sphenoethmoid recess. A low threshold for imaging in patients with low neutrophil or CD4 counts is advised. Goals include swift treatment of bacterial sinusitis and early identification of fungal sinusitis or neoplasm.

Recurrent Acute Sinusitis

Consider: nasal culture during episodes, CT imaging between episodes to identify anatomic abnormalities (e.g., septal deviation, concha bullosa), and allergic/immunologic evaluation.

Kartagener Syndrome

Sinusitis + bronchiectasis + situs inversus - due to inherited genetic defects in ciliary action.

Recent Evidence (2025)

A meta-analysis (Magboul et al., Rhinology 2025) supports budesonide nasal irrigation as an effective and safe treatment for chronic rhinosinusitis (PMID 39729039). An Italian intersociety consensus (2025) addressed sinusitis treatment in children, reinforcing antibiotic stewardship principles in the pediatric setting (PMID 40140854).

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