Sinusitis (Rhinosinusitis) — Causes, Symptoms, Diagnosis & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Sinusitis — more precisely rhinosinusitis — is inflammation of the mucosa of the paranasal sinuses (maxillary, frontal, ethmoid, and sphenoid), typically occurring in conjunction with nasal cavity inflammation. It is classified by duration: acute rhinosinusitis (ARS) lasts up to 4 weeks; subacute 4-12 weeks; chronic rhinosinusitis (CRS) persists beyond 12 weeks despite medical treatment. It is one of the most common medical conditions worldwide, generating enormous antibiotic prescriptions — yet 80-90% of acute cases are viral in origin and self-limiting, requiring no antibiotics. CRS with nasal polyps (CRSwNP) is a distinct eosinophilic inflammatory subtype associated with asthma, aspirin sensitivity (Samter's triad), and significantly impaired quality of life including anosmia. Rare but serious complications — orbital and intracranial extension — require emergency recognition.

Viral upper respiratory tract infections cause 80-90% of acute sinusitis — rhinovirus, coronavirus, adenovirus, and influenza virus. Bacterial secondary sinusitis occurs in approximately 0.5-2% of viral URTI cases — Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis are the main pathogens. Risk factors for CRS: allergic rhinitis (most important predisposing factor); nasal polyps (eosinophilic inflammation); deviated nasal septum or anatomical variants (concha bullosa, septal spur) obstructing the osteomeatal complex (key drainage area for the sinuses); immunodeficiency (IgA deficiency, CVID, CGD); cystic fibrosis and primary ciliary dyskinesia; asthma and NSAID sensitivity; GERD (reflux); dental infections (odontogenic sinusitis — up to 20% of maxillary sinusitis cases); and aspirin-exacerbated respiratory disease (Samter's triad: asthma + nasal polyps + aspirin sensitivity).

Major symptoms of rhinosinusitis: nasal blockage/congestion, anterior or posterior (post-nasal drip) mucopurulent nasal discharge, facial pain/pressure (site depends on sinus involved: maxillary — cheek pain; frontal — forehead pain; ethmoid — medial canthal/between-eyes pain; sphenoid — vertex/occipital — the 'forgotten sinus'), and hyposmia or anosmia (reduced or absent smell — often the most distressing symptom in CRS). Acute rhinosinusitis diagnosis: 2 or more symptoms including nasal blockage and/or discoloured nasal discharge, with or without facial pain/pressure and reduced smell. 'Double sickening' pattern — initial improvement after day 5 followed by worsening — suggests bacterial superinfection. Fever, unilateral pain, and tooth pain suggest bacterial sinusitis. Chronic rhinosinusitis (CRS): same cardinal symptoms for more than 12 weeks; with or without nasal polyps (visualised on endoscopy). CRS without nasal polyps (CRSsNP) tends to be bilateral facial pain/pressure; CRS with nasal polyps (CRSwNP) causes bilateral nasal obstruction and anosmia as dominant features.

Acute bacterial sinusitis is a clinical diagnosis — the ARIA/EPOS criteria identify bacterial sinusitis by: symptoms persisting beyond 10 days without improvement; or 'double sickening'; or severe symptoms (high fever above 38.5°C, severe unilateral facial pain, periorbital oedema) from the outset. Imaging is not recommended for acute sinusitis without suspected complications. For CRS: CT sinuses (gold standard) demonstrates mucosal thickening, air-fluid levels, osteomeatal complex obstruction, and polyp extent — Lund-Mackay score guides surgical decision-making. Nasal endoscopy: visualises nasal polyps, discharge, and anatomical variants. Allergy testing (skin prick test or specific IgE) for suspected allergic component. IGRA or ANCA for granulomatous causes (sarcoidosis, granulomatosis with polyangiitis). Swab of middle meatus for microbiological culture in CRS (identifies pathogens for targeted antibiotic therapy). Serum immunoglobulins (IgA, IgG, IgM) for suspected immunodeficiency. Sweat test and genetic testing if cystic fibrosis is suspected.

Viral acute rhinosinusitis (self-limiting, 7-10 days): high-volume nasal saline irrigation (hypertonic 2%, 240 mL twice daily — using neti pot or squeeze bottle — most evidence-based self-treatment); intranasal corticosteroids (mometasone furoate 200 mcg BD, fluticasone propionate 200 mcg BD — NICE-recommended for persistent symptoms beyond 10 days; modest but significant symptom reduction); analgesics (paracetamol, ibuprofen); steam inhalation (limited evidence but widely used). Bacterial acute sinusitis: amoxicillin-clavulanate 500/125 mg TDS for 5-7 days (first-line); doxycycline 100 mg BD if penicillin-allergic; co-trimoxazole if local resistance patterns dictate. Reserve antibiotics for clear evidence of bacterial disease — most improve without them. Chronic rhinosinusitis (CRS): prolonged high-dose intranasal corticosteroids (mometasone 200 mcg each nostril BD); nasal saline irrigation twice daily; systemic corticosteroids (short course — prednisolone 40 mg for 7-14 days) for polyp reduction before surgery; macrolide antibiotics long-course (low-dose azithromycin 250 mg 3x weekly for 12 weeks — anti-inflammatory not antibacterial effect) for CRSsNP. Biologics for CRSwNP: dupilumab (anti-IL-4Rα; anti-IL-4/13) — NICE approved for severe CRSwNP inadequately controlled by INCS and FESS — significantly reduces polyp score, improves olfaction and asthma control. Mepolizumab (anti-IL-5) alternative. Functional endoscopic sinus surgery (FESS): refractory CRS (despite maximal medical therapy); opens sinus drainage pathways endoscopically; significantly improves QoL, smell, and prevents recurrence with post-operative INCS and irrigation.

Most acute sinusitis is self-limiting, but certain forms — particularly aggressive bacterial rhinosinusitis — can cause serious and potentially life-threatening complications. Orbital complications: the ethmoid sinuses are adjacent to the orbit; infection can spread causing periorbital (pre-septal) cellulitis (eyelid redness and swelling), orbital cellulitis (post-septal — proptosis, ophthalmoplegia, reduced visual acuity — emergency requiring IV antibiotics and imaging), or subperiosteal orbital abscess (requiring surgical drainage). Orbital complications occur in approximately 3-4% of paediatric sinusitis cases and can cause permanent visual loss if not treated urgently. Intracranial complications (rare but life-threatening): meningitis (from frontal or sphenoid sinusitis spreading to the meninges); epidural or subdural empyema (pus between skull and dura — emergency neurosurgical drainage); brain abscess (frontal lobe from frontal sinusitis — presenting with frontal headache, personality change, and focal neurological deficits); and cavernous sinus thrombosis (bilateral eye signs, high fever, meningism — mortality 20-30% even with treatment). Pott's puffy tumour: frontal bone osteomyelitis from frontal sinusitis causing subperiosteal forehead abscess. Chronic rhinosinusitis leads to irreversible mucosal thickening, nasal polyp formation, anosmia, and significant quality of life impairment affecting work, sleep, and physical activity.

Annual influenza vaccination and pneumococcal vaccination reduce viral URTI and bacterial sinusitis incidence. Aggressive management of allergic rhinitis (allergen avoidance, antihistamines, intranasal corticosteroids, allergen immunotherapy) is the most effective preventive strategy for CRS. Daily nasal saline irrigation reduces recurrence rate of CRS by approximately 50% and prevents URTI-triggered flares. Manage GERD (proton pump inhibitors) as it contributes to mucosal irritation. Maintain adequate indoor humidity (40-60%) in winter heating season. Identify and treat dental infections promptly to prevent odontogenic maxillary sinusitis. Avoid tobacco smoke — impairs mucociliary clearance. After FESS: twice-daily nasal saline irrigation for at least 6 months; continue INCS indefinitely; regular endoscopic follow-up at 1, 3, 6, and 12 months post-surgery.

Go to Emergency Department immediately for any sinusitis with: periorbital swelling, redness, or eye movement limitation (orbital cellulitis or abscess — ophthalmic emergency); proptosis (forward protrusion of the eye); sudden severe headache, neck stiffness, photophobia, or altered consciousness (intracranial extension — meningitis, epidural/subdural abscess); fever with severe facial pain and swelling or rapid clinical deterioration. These are rare but potentially life-threatening complications requiring emergency CT, IV antibiotics, and surgical drainage. See your GP urgently for: symptoms persisting beyond 10 days without improvement; fever above 38.5°C with severe unilateral facial pain; any visual changes with sinus symptoms. Routine GP referral to ENT for: symptoms lasting more than 12 weeks despite medical treatment; suspected nasal polyps; recurrent acute sinusitis (more than 4 episodes per year).