Acute rhinosinusitis

Acute rhinosinusitis (ARS) is a self-limited inflammatory condition of the paranasal sinus mucosa and nasal cavity lasting up to four weeks, most commonly caused by viral upper respiratory infection with occasional secondary bacterial superinfection.[1][2] The maxillary and ethmoid sinuses are most frequently involved. Pathogenesis involves mucosal edema, impaired mucociliary clearance, and obstruction of the ostiomeatal complex, leading to fluid accumulation and sinus opacification.[3][4] On dental radiographs, ARS manifests as partial or complete radiopacity of the maxillary sinus, with or without an air-fluid level. Most episodes resolve spontaneously; management is primarily supportive, with antibiotics reserved for confirmed or presumed bacterial cases.[1][2]

• Acute rhinosinusitis (ARS) is the current preferred term, reflecting the near-universal concurrent involvement of the nasal mucosa and paranasal sinuses.[2]
• ARS is subclassified by presumed etiology:
  • Viral rhinosinusitis (VRS): symptoms present [2]
  • Acute bacterial rhinosinusitis (ABRS): symptoms persisting ≥10 days without improvement, or worsening within 10 days after initial improvement ("double worsening")[2]
• Recurrent acute rhinosinusitis (RARS): four or more annual episodes of ABRS without persistent symptoms between episodes[2]
• The older term "sinusitis" remains in widespread clinical use but is considered less precise.[2]
• Duration-based classification: acute (12 weeks).[1][2]

• Approximately 12% of U.S. adults report a rhinosinusitis diagnosis annually, generating over 30 million patient encounters per year.[2][5]
• Women are affected more frequently than men (13.3% vs. 9.0% in U.S. survey data), with peak prevalence in adults aged 45–74 years.[5][6]
• Viruses cause 90–98% of ARS episodes; only 0.5–2% of viral upper respiratory infections progress to ABRS.[1][6]
• Approximately 20 million cases of presumed ABRS occur annually in the United States.[2]
• The most common bacterial pathogens are Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis; Staphylococcus aureus is an occasional pathogen in adults.[1][7]
• Common viral pathogens include rhinovirus, coronavirus, respiratory syncytial virus, adenovirus, and metapneumovirus.[5]

Symptoms and presentation

• Cardinal symptoms: purulent nasal discharge accompanied by nasal obstruction, facial pain/pressure/fullness, or both.[1][2]
• Additional common symptoms include headache, postnasal drip, cough, hyposmia, low-grade fever, and malaise.[5][8]
• Facial pain location may suggest the involved sinus: cheek pain (maxillary), forehead (frontal), medial canthus (ethmoid), occiput (sphenoid).[8]
• Dental pain in the posterior maxilla is common when the maxillary sinus is involved, particularly with odontogenic sources.[8][9]

Distinguishing bacterial from viral ARS

• VRS symptoms typically peak at days 3–5 and resolve within 7–10 days.[1]
• ABRS is diagnosed clinically when symptoms persist ≥10 days without improvement, or worsen within 10 days after initial improvement.[1][2]
• Features suggesting severe ABRS include high fever (≥39°C), unilateral facial pain, and purulent nasal discharge lasting ≥3 days.[5]

Complications and red flags

• Orbital complications (preseptal cellulitis, orbital abscess, subperiosteal abscess) are the most common serious complications, typically arising from ethmoid sinusitis.[10][11]
• Intracranial complications (epidural/subdural abscess, brain abscess, meningitis, cavernous sinus thrombosis) are less common but carry significant morbidity and mortality; they occur most often in adolescent males with frontal sinusitis.[10][12]
• Red flags warranting urgent evaluation: periorbital swelling, proptosis, impaired extraocular motility, visual changes, severe headache, altered mental status, and focal neurologic deficits.[10]

Imaging is not recommended for uncomplicated ARS meeting clinical diagnostic criteria.[2] However, dental radiologists frequently encounter incidental sinus findings on routine dental imaging, and recognition of ARS-related changes is essential for appropriate referral.

Location and distribution

• The maxillary sinus is the most commonly affected sinus visible on dental radiographs, owing to its anatomic proximity to the posterior maxillary dentition.[11][13]
• Involvement is often unilateral in odontogenic sinusitis but may be bilateral in rhinogenic ARS.[9][14]
• The ethmoid sinuses are frequently co-involved but are not well visualized on conventional dental radiographs.[13]

Periphery and shape

• The normal thin cortical outline of the maxillary sinus floor may become indistinct or obscured by adjacent mucosal thickening or fluid.[15][16]
• Loss of the sharp cortical line of the sinus floor on periapical radiographs, particularly adjacent to teeth with periapical pathology, suggests extension of inflammation into the sinus.[15][17]

Internal architecture

• Mucosal thickening: appears as a band-like radiopacity along the sinus walls, most readily identified along the sinus floor on periapical and panoramic radiographs. Generalized mucosal thickening is the most prevalent sinus abnormality on CBCT, observed in approximately 65% of sinuses with disease.[18]
• Air-fluid level: a horizontal radiopaque line with a sharp superior border demarcating fluid from air, best seen on upright imaging. On CBCT, air-fluid levels are well demonstrated in coronal and sagittal reconstructions and may contain scattered air bubbles within the fluid.[3][4]
• Complete sinus opacification: total radiopacity of the sinus cavity, which may represent extensive mucosal disease, retained secretions, or a combination. Complete opacification is nonspecific and requires clinical correlation to distinguish infection from other causes.[3][19]
• Localized dome-shaped radiopacity: a well-circumscribed, dome-shaped soft-tissue density arising from the sinus floor or walls represents either localized mucosal thickening or a mucous retention cyst; these are common incidental findings and should not be confused with acute sinusitis.[3][18]

Effects on adjacent structures

• Periapical lesions of maxillary premolars and molars may extend to or through the sinus floor, producing localized mucosal thickening or discontinuity of the sinus floor cortex. The first molar is the tooth most frequently associated with odontogenic sinus disease.[13][17][18]
• In uncomplicated ARS, teeth adjacent to the involved sinus are typically vital and show no root resorption or displacement.
• Bony changes such as osteolysis, demineralization, or subperiosteal edema of the sinus walls are not features of uncomplicated viral ARS; their presence suggests bacterial or fungal superinfection or an alternative diagnosis.[3]

Extent and cortical involvement

• Uncomplicated ARS does not cause expansion, cortical destruction, or erosion of the sinus walls.[3][20]
• Cortical erosion, wall expansion, or extra-sinus soft-tissue extension are red flags for complicated infection, invasive fungal sinusitis, or neoplasm and warrant urgent advanced imaging.[2][3]

Limitations of dental radiographs

• Panoramic radiography has low sensitivity (approximately 37%) for detecting maxillary sinus mucosal thickening compared with CBCT, though specificity is high.[21]
• Periapical radiographs can identify sinus floor discontinuity and gross opacification but cannot reliably characterize the extent or nature of sinus disease.[15][22]
• CBCT provides superior three-dimensional assessment of the tooth–bone–sinus complex and is valuable when an odontogenic source is suspected or when conventional radiographs are inconclusive.[23][24]

CT without contrast

• Non-contrast CT of the paranasal sinuses is the standard medical imaging modality for evaluating ARS when complications or an alternative diagnosis are suspected. Findings include mucosal thickening, air-fluid levels, and partial or complete sinus opacification. The Lund-Mackay scoring system quantifies opacification across all sinuses and the ostiomeatal complex on a 0–24 scale and is the most widely used staging tool.[2][3][25][26]
• Osseous destruction, extra-sinus extension, or infratemporal surface erosion on CT suggest neoplasm rather than inflammatory disease.[2][20]

Contrast-enhanced CT

• Indicated when orbital or intracranial complications are suspected. Abscesses appear as low-density collections with an enhancing rim. Contrast-enhanced CT is the first-line study for evaluating preseptal/postseptal orbital involvement and intracranial extension.[3][10]

MRI

• MRI is complementary to CT when fungal sinusitis, mucocele, or sinonasal neoplasm must be excluded. Inflamed mucosa in ARS demonstrates T2 hyperintensity and enhances with gadolinium, whereas inspissated secretions and fungal concretions show T2 hypointensity. MRI is superior for distinguishing tumor from obstructed secretions and for evaluating perineural or intracranial spread.[3][25][27][28]

Sinus opacification on dental radiographs is nonspecific. The following entities most commonly enter the differential when maxillary sinus radiopacity is encountered on dental imaging.

The highest-risk diagnostic pitfall is misinterpreting a sinonasal neoplasm as inflammatory sinusitis. Any unilateral sinus opacification with cortical destruction, wall expansion, or failure to respond to medical therapy warrants contrast-enhanced CT or MRI and otolaryngologic referral to exclude malignancy.[2][25]

Histopathologic examination of sinus mucosa is not routinely performed in uncomplicated ARS but may be obtained during surgical management of complicated cases.

Microscopic findings

• The lamina propria shows the most prominent changes: marked edema, extensive neutrophilic infiltration, microabscess formation, thrombophlebitis of small vessels, and focal necrosis.[31]
• Epithelial involvement is comparatively modest, with preservation of the pseudostratified ciliated columnar epithelium in early disease; epithelial degeneration occurs in more severe infections.[31][32]
• Luminal exudates composed of neutrophils, fibrin, and cellular debris are characteristic.[32]
• Immunohistochemistry demonstrates increased T lymphocytes (diffusely scattered) and B lymphocytes (clustered around venules, seromucous glands, and subepithelially), suggesting active immune cell recruitment from the bloodstream.[31]

Distinction from chronic sinusitis

• Complicated sinusitis demonstrates a lymphoplasmacytic-predominant infiltrate with enhanced neutrophilic component, distinguishing it from chronic rhinosinusitis with nasal polyps (CRSwNP), which is typically eosinophil-predominant.[33]
• Chronic sinusitis shows basement membrane thickening, submucosal fibrosis, goblet cell hyperplasia, and squamous metaplasia—features absent in acute disease.[31][33]

Supportive care

• Approximately 85% of ARS episodes resolve spontaneously within 7–15 days without antibiotics.[1]
• Symptomatic relief measures include analgesics, nasal saline irrigation, topical intranasal corticosteroids, and short-term decongestants.[1][2]

Antibiotic therapy

• Watchful waiting without antibiotics is recommended as initial management for uncomplicated ABRS, provided follow-up is assured.[1][2]
• When antibiotics are initiated, amoxicillin with or without clavulanate for 5–7 days is first-line therapy.[2][34]
• For beta-lactam allergy: doxycycline or a respiratory fluoroquinolone in adults.[5]
• Treatment failure (no improvement after 3–5 days of appropriate antibiotics) requires reassessment to confirm the diagnosis, exclude complications, and change the antibiotic regimen.[2]

Odontogenic source management

• When an odontogenic etiology is identified, definitive dental treatment (endodontic therapy, extraction, or management of oroantral communication) is essential for resolution. Sinus mucosal changes typically resolve within approximately 3 months after successful dental treatment.[15][24][29]

Complicated ARS

• Orbital or intracranial complications require hospitalization, intravenous antibiotics, and urgent contrast-enhanced imaging.[10]
• Surgical intervention (endoscopic sinus surgery, abscess drainage) is indicated for subperiosteal or orbital abscess, intracranial abscess, or failure of medical therapy.[11][12]
• Neurologic complications carry approximately 30% long-term morbidity, including vision loss, seizures, and hemiparesis.[12]

Prognosis

• Uncomplicated ARS has an excellent prognosis. Serious complications are rare but can be life-threatening if not promptly recognized and treated.[1][12]
• Recurrent episodes (≥4/year) should prompt evaluation for underlying predisposing factors including allergic rhinitis, anatomic variants, immunodeficiency, or unrecognized odontogenic sources.[2][6]