What is the significance of CT scan findings in a patient suspected of having Chronic Rhinosinusitis (CRS)?

CT Findings and Significance in Chronic Rhinosinusitis

CT scan remains the gold standard for radiologic confirmation of CRS, with a Lund-Mackay score ≥5 providing excellent positive predictive value for true disease, though CT findings correlate poorly with symptom severity and should primarily guide surgical planning rather than medical management decisions. 1

Key CT Findings That Confirm CRS

CT demonstrates several characteristic findings that objectively document sinonasal inflammation:

• Mucosal thickening within the paranasal sinuses 1
• Sinus opacification (partial or complete) 1
• Polyps or retention cysts 1
• Sclerosis and thickening of sinus walls (particularly in chronic disease) 1
• Ostiomeatal complex obstruction 1

Diagnostic Performance and Scoring

The Lund-Mackay scoring system is the validated standard for quantifying CT findings, scoring each sinus (maxillary, anterior ethmoids, posterior ethmoids, frontal, sphenoid) as 0 (no opacification), 1 (partial), or 2 (complete), plus 0 or 2 for ostiomeatal complex, yielding a maximum score of 24 (12 per side). 1

Critical diagnostic thresholds:

• LMS ≤2: Excellent negative predictive value; essentially rules out CRS (sensitivity 94%, specificity 41%) 1
• LMS ≥5: Excellent positive predictive value for true disease (pediatric data: sensitivity 86%, specificity 85%) 1
• LMS 3-4: Clinically relevant disease warranting treatment consideration 1

When CT Is Essential vs. Optional

CT is essential after:

• Failure of appropriate medical treatment in secondary care with continued symptoms AND abnormal endoscopy 1
• Before functional endoscopic sinus surgery for surgical planning 1
• When complications are suspected (orbital, intracranial) - use CT with contrast or MRI 1
• When neoplasia or invasive fungal sinusitis is suspected 1

CT is NOT essential at:

• Initial presentation to ENT/secondary care, even with highly suggestive symptoms (consensus unclear among experts, with 52% rating it as moderately important and 41% rating it as not essential) 1
• Acute rhinosinusitis (diagnosis is clinical; CT is overused in this context) 1

Critical Pitfall: Poor Symptom Correlation

The most important caveat is that CT findings correlate weakly or not at all with symptom severity in most CRS patients. 1, 2

• No association exists between total SNOT-22 scores and Lund-Mackay scores in CRS without nasal polyps 1
• The only symptom that significantly correlates with CT scores is olfaction 1
• Facial pain shows inverse correlation with CT findings in CRS without polyps (higher pain scores = lower LMS, p=0.022) 1
• Some correlation exists in CRS with nasal polyps subgroup, but remains weak overall 1

This means CT severity does not predict quality of life impairment or guide medical treatment intensity - it primarily serves to confirm diagnosis and plan surgery. 1, 2

Surgical Planning Value

CT is critical for identifying anatomic variants and abnormalities that increase surgical risk:

• Cribriform plate dehiscence or asymmetry 1
• Lamina papyracea integrity (orbital wall) 1
• Anterior ethmoidal artery canal location 1
• Onodi cells and sphenoid sinus variants 1
• Carotid artery dehiscence 1

Low-dose CT protocols are inadequate for visualizing these surgically critical structures, particularly in patients with nasal polyps or prior surgery. 1

Contrast Enhancement

Contrast is NOT needed for:

• Routine CRS diagnosis 1
• Surgical planning for uncomplicated inflammatory disease 1

Contrast IS needed for:

• Suspected orbital or intracranial complications 1
• Suspected neoplasia 1
• Suspected invasive fungal sinusitis 1

Alternative Imaging Modalities

• Cone beam CT: Accurate for CRS diagnosis with lower radiation, but limited soft-tissue evaluation; not preferred if extrasinus disease suspected 1
• MRI: Superior for differentiating inflammation from neoplasia; useful when complications suspected or radiation exposure is a concern 1, 3, 4
• Plain radiography: Inadequate; no longer recommended 1, 4

Stability of CT Findings Over Time

CT findings in untreated CRS patients remain relatively stable over short to middle time intervals (mean 338 days), with Lund-Mackay scores showing strong correlation (r=0.86) between serial scans regardless of initial disease severity. 5 This suggests repeating CT scans in symptomatic untreated patients should be seriously questioned unless clinical status has significantly changed. 5