What imaging modalities are recommended for preseptal cellulitis?

Imaging for Preseptal Cellulitis

Imaging is generally not required for uncomplicated preseptal cellulitis when the clinical diagnosis is clear, but CT orbits with IV contrast should be obtained immediately if clinical findings cannot reliably distinguish preseptal from orbital cellulitis or if there are any concerning features suggesting postseptal involvement. 1, 2

When Imaging is NOT Needed

• Preseptal cellulitis is primarily a clinical diagnosis that does not require imaging when the presentation is straightforward. 2, 3
• The American College of Radiology guidelines state that imaging should be reserved for cases where clinical examination alone cannot reliably differentiate preseptal from orbital cellulitis. 1
• Uncomplicated preseptal cellulitis presents with diffuse periorbital erythema and edema, warmth, and tenderness confined to the eyelid and tissues anterior to the orbital septum, without proptosis, normal extraocular movements, and preserved vision. 2

Absolute Indications for Immediate CT Imaging

Obtain CT orbits with IV contrast emergently if ANY of the following are present: 1, 4

• Proptosis (indicates postseptal involvement) 1
• Impaired or painful extraocular movements 1, 4
• Ophthalmoplegia 4, 5
• Decreased visual acuity 4, 5
• Gross periorbital edema with eyelid >50% closed 2, 4
• Age >3 years with significant periorbital swelling 1, 4
• High neutrophil count 1, 4
• Previous antibiotic therapy without improvement after 24-48 hours 1, 2
• Inability to adequately examine the eye 2
• Systemic signs of toxicity 2

Recommended Imaging Modality

• CT orbits with IV contrast is the most useful imaging modality for suspected orbital infection. 1
• CT accurately differentiates preseptal cellulitis from postseptal cellulitis and abscess, detects subperiosteal abscesses (particularly along the medial orbital wall from ethmoid sinusitis), identifies underlying sinusitis, and assesses for bone erosion. 1, 4
• Precontrast imaging is not necessary as it does not add significant diagnostic information in this scenario. 1, 4

When to Add Additional Imaging

Add CT head with IV contrast if intracranial complications are suspected: 1, 4

• Subdural empyema 1, 4
• Cavernous sinus thrombosis 1, 4
• Meningitis or cerebritis 5
• Frontal bone osteomyelitis 4

Consider MRI head and orbits with and without IV contrast as complementary imaging when: 1

• More detailed assessment of intraorbital spread is clinically warranted 1
• Clinical or CT-based suspicion for intracranial complications exists 1, 4
• CT is non-diagnostic but clinical suspicion remains high 6

Critical Pitfalls to Avoid

• Do not rely on clinical examination alone to distinguish preseptal from orbital cellulitis, as proptosis and limitation of extraocular movements are not accurate enough to differentiate postseptal inflammation from abscess. 1, 5
• Assuming all periorbital infections are preseptal cellulitis can delay diagnosis of orbital cellulitis, which requires urgent intervention to prevent vision loss, cavernous sinus thrombosis, or intracranial extension. 2, 5, 6
• Plain radiographs are insufficient to detect orbital pathology and have been supplanted by CT. 1, 4
• Point-of-care ultrasound may help differentiate preseptal from orbital cellulitis but cannot exclude intracranial extension of infection. 6

Special Considerations

• In children with preseptal cellulitis secondary to sinusitis (particularly ethmoid sinusitis) or dental abscess, maintain a lower threshold for imaging as these have higher risk of postseptal extension. 1, 4, 7
• C-reactive protein >120 mg/L suggests orbital rather than preseptal involvement and should prompt imaging. 7
• Fever is present in 51.5% of preseptal cellulitis cases versus 82.2% of orbital cellulitis cases, but this alone should not guide imaging decisions. 7