CT Scan Indications in Sinusitis
CT imaging is not indicated for acute uncomplicated sinusitis but becomes appropriate when complications develop, when symptoms persist despite adequate medical therapy (≥12 weeks for chronic rhinosinusitis), or before planned surgical intervention. 1
When CT Scan is NOT Indicated
Acute uncomplicated rhinosinusitis does not require imaging, as the distinction between viral and bacterial infection is a clinical diagnosis that should be made based on symptom duration and pattern rather than radiographic findings. 1
Symptoms alone without objective documentation are insufficient for diagnosis, and imaging should not be ordered based solely on non-specific complaints like halitosis or postnasal drip without accompanying sinus-specific symptoms. 2
Plain radiographs are largely obsolete due to high inaccuracy rates and have been supplanted by CT when imaging becomes necessary. 1
Absolute Indications for CT Scan
Suspected Complications (Urgent)
Orbital complications: facial swelling, orbital proptosis, periorbital edema, vision changes, or ophthalmoplegia warrant immediate CT with IV contrast to detect orbital cellulitis, subperiosteal abscess, or orbital abscess (87-91% accuracy). 1, 3, 4
Intracranial complications: severe headache, altered mental status, cranial nerve palsies, or meningeal signs require CT with IV contrast, though MRI with contrast is superior (97% accuracy) for detecting epidural abscess, subdural empyema, meningitis, or brain abscess. 1, 3, 4
Invasive fungal sinusitis: immunocompromised patients with fever and sinus symptoms require urgent non-contrast CT initially, with contrast added if orbital or intracranial extension is suspected. 3
Pre-Surgical Planning
Non-contrast CT is mandatory before functional endoscopic sinus surgery to delineate complex ethmoidal anatomy, ostiomeatal unit obstruction, and anatomic variations (including Onodi cells that increase risk of optic nerve or carotid artery injury). 1
CT provides essential information for computer navigation systems used during endoscopic sinus surgery, with accuracy within 2 mm. 1
Chronic or Recurrent Disease
Recurrent acute rhinosinusitis (RARS): Four or more episodes annually warrant non-contrast CT for objective confirmation and to identify anatomic variants, foreign bodies, or underlying structural abnormalities. 1
Chronic rhinosinusitis (≥12 weeks of symptoms): CT is indicated after failure of appropriate medical therapy (including intranasal corticosteroids and antibiotics) to confirm diagnosis and guide further management. 5
Symptoms alone have only 37-73% sensitivity for chronic rhinosinusitis diagnosis, and up to 35% of patients have normal endoscopic findings, making CT critical for objective documentation. 5
Special Circumstances
Suspected odontogenic sinusitis: Maxillary sinusitis may be dental in origin in 10-12% of cases; CBCT or standard CT can identify periapical infections spreading from molar teeth. 1
Unilateral disease: Persistent unilateral symptoms raise concern for anatomic variants, fungal disease (fungus ball), or neoplasm requiring CT evaluation. 1
Immunocompromised patients with fever: These patients require urgent imaging due to increased risk of serious complications including invasive fungal infection. 6
Timing Considerations
Wait at least 2 weeks after an upper respiratory infection and 4 weeks after acute bacterial sinusitis before obtaining CT to avoid false-positive findings from transient mucosal inflammation. 1
Imaging should be performed after appropriate medical management has been attempted to identify true underlying chronic disease rather than acute inflammatory changes. 1
CT Protocol Selection
Non-contrast CT is the standard protocol for uncomplicated sinusitis, providing optimal visualization of bone anatomy, sinus drainage pathways, and mucosal disease without unnecessary radiation exposure. 3
Add IV contrast only when evaluating for complications: orbital involvement, intracranial extension, vascular complications, or suspected mass lesions. 3
Avoid dual-phase imaging (both non-contrast and contrast) as it doubles radiation exposure without additional diagnostic yield. 3
Alternative Imaging Modalities
MRI with contrast is superior to CT for soft-tissue differentiation in cases of suspected sinonasal mass, skull base dehiscence, intracranial extension, or invasive fungal sinusitis, though it poorly visualizes bone anatomy. 1, 4
Nasal endoscopy is preferred over imaging as the initial diagnostic step for evaluating postnasal drip and non-specific symptoms, providing direct visualization of the nasopharynx and documenting inflammation. 2, 5
Critical Pitfall to Avoid
- CT findings do not correlate with symptom severity in chronic sinusitis, so imaging abnormalities must be interpreted in conjunction with clinical findings to avoid overdiagnosis—up to 40% of symptomatic adults and 18-82% of asymptomatic individuals show incidental sinus abnormalities on CT. 2, 6, 7, 8