Sinusitis (Sinus Infection)
Sinusitis
Sinusitis — more precisely termed rhinosinusitis, as the nasal lining is invariably involved alongside the sinus lining — is inflammation of the mucosa of the paranasal sinuses. It is one of the most prevalent conditions managed in both primary and specialist medical care, affecting an estimated 12–15% of the adult population at any given time in developed countries. Understanding sinusitis requires familiarity with the anatomy of the paranasal sinuses, the mechanisms by which they become inflamed or infected, the important distinction between acute and chronic disease, and the evidence base for the treatments currently available.
For an overview of all sinus conditions managed by Dr Roth, see the Sinus Problems page →
The Paranasal Sinuses — Anatomy
The paranasal sinuses are paired air-filled cavities within the bones of the skull, named according to the bone in which they are situated. Four pairs of sinuses exist:
All sinuses are lined with pseudostratified columnar epithelium with cilia and goblet cells. The cilia beat rhythmically at approximately 700–1,000 strokes per minute, moving the mucus blanket toward the sinus ostia and into the nasal cavity. This mucociliary transport is essential for keeping the sinuses clear of inhaled particles, pathogens, and cellular debris. When mucociliary function is impaired — by viral infection, allergy, environmental pollutants, or ciliary disease — mucus accumulates and infection becomes more likely.
The ostiomeatal complex (OMC) is a functionally critical region in the lateral nasal wall where the drainage pathways of the maxillary, anterior ethmoid, and frontal sinuses converge. Blockage of the OMC — from mucosal swelling, polyps, anatomical variants, or structural obstruction — impairs drainage from all three sinuses simultaneously and is a key target of endoscopic sinus surgery.
Classification of Rhinosinusitis
Acute Rhinosinusitis
Sinusitis lasting fewer than 12 weeks, with complete resolution of symptoms between episodes. Most commonly follows viral upper respiratory tract infection (URTI). Viral rhinosinusitis affects approximately 1 in 8 people per year. The distinction between viral and secondary bacterial acute rhinosinusitis is clinically important because most cases are viral and do not benefit from antibiotics:
- Viral: Symptoms typically peak at 2–3 days and improve by days 7–10. The presence of purulent nasal discharge does not reliably distinguish viral from bacterial disease.
- Bacterial (acute): Suggested by symptom duration beyond 10 days without improvement, severe symptoms (high fever ≥39°C, severe unilateral facial pain), or biphasic illness — initial improvement followed by worsening around day 5–6. The most common pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.
Recurrent Acute Rhinosinusitis
Defined as four or more episodes of acute bacterial rhinosinusitis per year, with complete symptom resolution between episodes. Patients with recurrent acute sinusitis often have predisposing anatomical or mucosal factors that warrant investigation and potentially surgical treatment.
Chronic Rhinosinusitis (CRS)
Inflammation of the sinonasal mucosa persisting for 12 weeks or more, diagnosed when at least two of the following cardinal symptoms are present: nasal obstruction or blockage, nasal discharge or post-nasal drip, facial pain or pressure, and reduction or loss of smell (anosmia). CRS is subdivided into CRS without nasal polyps (CRSsNP) and CRS with nasal polyps (CRSwNP), which have distinct pathophysiological profiles and response to treatment. A third category — allergic fungal rhinosinusitis — requires specific diagnosis and management.
Subacute Rhinosinusitis
Sinusitis lasting 4–12 weeks — a transitional category sometimes used clinically to describe sinusitis that has not resolved but has not yet become chronic.
Pathophysiology — How Sinusitis Develops
The development of sinusitis begins with impairment of the normal sinus ventilation and mucociliary clearance mechanisms. The sequence is well understood for acute sinusitis following viral URTI:
- Viral infection of the nasal mucosa produces oedema, increased mucus production, and ciliary dysfunction.
- Swelling of the mucosa at the ostiomeatal complex obstructs drainage from the maxillary and frontal sinuses.
- Negative pressure develops within the obstructed sinus as oxygen is absorbed; this draws nasal secretions — including bacteria — into the sinus via the ostium.
- The warm, nutrient-rich environment of the sinus, combined with reduced mucociliary clearance, allows bacterial proliferation.
- Pus accumulates within the sinus, generating further pressure, pain, and local inflammation.
In chronic rhinosinusitis the pathophysiology is more complex and less fully understood. Current evidence supports a model in which an aberrant immune response to colonising organisms — possibly bacteria, fungi, or both — drives persistent mucosal eosinophilic inflammation in patients with a genetic predisposition. This explains why CRS often persists despite treatment of infection and why anti-inflammatory strategies (corticosteroids, biologics) are central to its management.
Symptoms in Detail
Nasal Obstruction
Mucosal oedema and increased secretions reduce the nasal airway. In chronic disease, turbinate hypertrophy and nasal polyps may contribute to persistent obstruction that does not fully resolve between episodes.
Facial Pain and Pressure
The character and location of pain reflects which sinuses are involved. Maxillary sinusitis produces cheek pain and fullness, sometimes radiating to the upper teeth. Ethmoiditis causes pain between and behind the eyes. Frontal sinusitis produces forehead pain, often worse in the morning and on leaning forward. Sphenoid sinusitis causes deep, poorly localised headache. Important caveat: the majority of patients who self-diagnose “sinus headache” actually have migraine or tension-type headache — the absence of nasal symptoms makes a primary headache disorder more likely, and ENT assessment with nasendoscopy and CT is essential to confirm or exclude sinus pathology before attributing headache to the sinuses.
Loss of Smell (Anosmia)
Olfactory dysfunction in sinusitis can be conductive (obstruction preventing odorants from reaching the olfactory epithelium) or sensorineural (direct damage to olfactory neurons from chronic mucosal inflammation or viral infection). CRS with nasal polyps typically causes conductive anosmia that improves substantially with appropriate treatment. Post-viral olfactory loss — increasingly recognised following COVID-19 — is predominantly sensorineural and may not respond to treatment.
Post-Nasal Drip and Chronic Cough
Excessive or abnormally thick mucus draining posteriorly from inflamed sinuses causes throat irritation, a chronic need to clear the throat, and a cough that is typically worse in the supine position. This is a very common presenting complaint in patients with CRS and may be the dominant symptom in some.
Fatigue and Systemic Effects
Chronic rhinosinusitis has measurable effects on quality of life comparable to chronic medical conditions such as congestive heart failure and diabetes in validated health status measures. Chronic sleep disruption from nasal obstruction, recurrent infections, and the physical burden of chronic inflammation all contribute to fatigue and reduced daytime function.
When to Seek Assessment
- Swelling or redness around the eye or orbit — periorbital or orbital cellulitis
- Proptosis (forward displacement of the eye) or restricted eye movement
- Severe headache with neck stiffness, altered consciousness, or photophobia — suggesting meningitis
- High fever with a toxic clinical appearance
- Forehead swelling — Pott’s puffy tumour, a subperiosteal abscess of the frontal sinus
These rare but serious complications of acute sinusitis represent intracranial or orbital spread of infection and require emergency hospital admission.
Routine ENT assessment is appropriate when:
- Symptoms persist beyond 10 days without improvement despite appropriate first-line treatment
- Symptoms are recurrent — three or more episodes in six months
- Significant loss of smell is present
- Symptoms suggest CRS (present for more than 12 weeks)
- Symptoms are disproportionate, unilateral, or there is concern about an alternative diagnosis
Investigation
Nasal Endoscopy
The cornerstone of ENT assessment for sinusitis. A thin, rigid telescope is passed through each nostril under topical anaesthetic to directly visualise the nasal septum, inferior and middle turbinates, and the middle meatus — where the ostiomeatal complex is located. Nasal polyps, purulent discharge from sinus ostia, mucosal oedema, and structural abnormalities (deviated septum, Haller cells, concha bullosa) can all be identified. Endoscopy is far more informative than anterior rhinoscopy with a speculum and is essential for any patient with suspected CRS.
CT Scanning
High-resolution CT of the sinuses is the standard imaging investigation for sinusitis. It provides detailed anatomical information about the extent and distribution of sinus disease, the anatomy of the drainage pathways, and any structural variants or complications. CT should not be performed during an acute episode of sinusitis — acute mucosal oedema produces opacification of normal sinuses that is indistinguishable radiologically from chronic disease, and CT findings will not accurately represent the baseline anatomy. Scanning is best performed after appropriate medical treatment has been completed. CT is an essential prerequisite for any sinus surgery.
Allergy Testing
Skin prick testing or specific serum IgE measurement is appropriate in patients with suspected allergic rhinitis contributing to sinusitis. Identifying the specific allergen(s) guides avoidance strategies and determines suitability for allergen immunotherapy, which can reduce the long-term burden of allergic rhinosinusitis.
Microbiological Swab
An endoscopically directed culture swab from the middle meatus can identify the causative organism and antibiotic sensitivities in cases not responding to empirical antibiotics, or in immunocompromised patients.
Treatment
Acute Rhinosinusitis — Medical Management
The majority of acute rhinosinusitis episodes are viral and resolve without antibiotics. The EPOS (European Position Paper on Rhinosinusitis and Nasal Polyps) guidelines recommend:
- Saline nasal irrigation (high-volume, isotonic or hypertonic) — reduces mucosal oedema, washes out secretions and inflammatory mediators, and improves mucociliary function. A grade A recommendation for all forms of rhinosinusitis.
- Topical nasal corticosteroids — reduce mucosal oedema at the ostiomeatal complex, improving drainage. Recommended for moderate-severe acute rhinosinusitis and as monotherapy for mild acute CRS.
- Antibiotics — indicated only for bacterial acute sinusitis (symptom duration beyond 10 days, severe symptoms, or biphasic illness). Amoxicillin-clavulanate is the first-line oral antibiotic in Australia (based on resistance patterns). A 5–7 day course is typically sufficient for uncomplicated acute bacterial rhinosinusitis.
- Short course oral corticosteroids — for severe acute sinusitis causing significant pain or marked nasal obstruction, a brief course reduces mucosal oedema. Not for routine use.
- Decongestants (topical oxymetazoline) — provide short-term symptomatic relief by reducing nasal mucosal engorgement. Limit to 3–4 days of use due to rebound congestion.
Chronic Rhinosinusitis — Medical Management
The EPOS guidelines recommend a stepwise approach for CRS:
- Intranasal corticosteroids (INS): The most important medical treatment for CRS with and without nasal polyps. Used twice daily — correct technique (directing the spray laterally toward the turbinate rather than medially toward the septum) is essential. Should be continued long-term. In CRS with nasal polyps, higher doses or nasal corticosteroid drops or sprays designed for polyp penetration may be used.
- High-volume saline nasal irrigation: Daily irrigation with isotonic saline significantly reduces symptom burden and is recommended as routine adjunct therapy. Hypertonic solutions may provide additional benefit for thick secretions.
- Prolonged low-dose macrolide antibiotics: Macrolides (clarithromycin, roxithromycin) have anti-inflammatory as well as antimicrobial properties. A 12–24 week course at low dose benefits CRS without polyps patients with low IgE, particularly those with bacterial biofilm formation. Not effective for CRSwNP.
- Oral corticosteroids: Short courses are effective for CRSwNP — they reduce polyp bulk, improve smell, and reduce the need for surgery. Not suitable for long-term use due to systemic side effects.
- Biological agents (dupilumab, mepolizumab): Monoclonal antibodies targeting the type 2 inflammatory pathway (dupilumab targets IL-4/IL-13; mepolizumab targets IL-5) are now available for severe CRSwNP not controlled by corticosteroids. They represent a significant advance for the most difficult-to-treat patients and are PBS-subsidised in Australia for appropriate cases. Assessment by a specialist is required for prescribing.
Surgical Treatment — FESS
Functional endoscopic sinus surgery (FESS) is recommended when appropriate medical treatment has failed to achieve adequate symptom control over 12 weeks. It is the standard surgical approach for chronic rhinosinusitis, nasal polyps, and recurrent acute sinusitis. Read in detail about sinus surgery →
Contact us to arrange a consultation → | Sinus Problems → | Sinus Surgery (FESS) → | Nasal Polyps →
Dr Roth’s Clinical Perspective
The distinction between acute sinusitis that needs antibiotics and viral rhinosinusitis that does not is one of the most practically important in ENT. The duration and pattern of symptoms — not the colour of the discharge or the appearance of the throat — is what guides the diagnosis. Symptoms improving then worsening, or symptoms persisting beyond ten days without any improvement, are the patterns that suggest bacterial involvement and justify antibiotic treatment. A single episode of acute sinusitis that responds to treatment does not require specialist referral. Recurrent episodes, persistent symptoms, or failure to respond to appropriate treatment are the referral indications.
— Dr Jason Roth, MBBS, FRACS (ORL-HNS), IBCFPRS
Specialist Otolaryngologist & Head and Neck Surgeon
Specialist registration — Otorhinolaryngology, Head & Neck Surgery
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