When should a repeat computed tomography (CT) scan of the face/orbit/neck be performed in a patient with facial cellulitis who shows clinical deterioration or fails to improve after 48–72 hours, or who is high‑risk (e.g., immunocompromised, diabetic, elderly, or with sinus disease)?

Repeat CT Imaging in Facial Cellulitis

Repeat CT scanning of the face/orbit/neck should be performed immediately if clinical deterioration occurs at any time, or after 48–72 hours of appropriate antibiotic therapy if no improvement is observed, particularly in high-risk patients (immunocompromised, diabetic, elderly, or those with sinus disease). 1, 2

Immediate Indications for Repeat CT (Do Not Wait)

Obtain emergent repeat CT imaging if any of the following develop at any point during treatment:

• New or worsening proptosis – signals progression from preseptal to postseptal (orbital) involvement or abscess formation 1, 2
• New limitation or pain with extraocular movements – indicates orbital muscle involvement or abscess compressing orbital structures 1, 3
• Decreased visual acuity or vision changes – suggests optic nerve compression, orbital apex syndrome, or intracranial extension 1, 3, 4
• Severe pain disproportionate to examination findings – raises concern for necrotizing infection or deep fascial involvement 5, 2
• Development of ophthalmoplegia – indicates cranial nerve involvement or cavernous sinus thrombosis 1, 6
• New neurological signs (altered mental status, confusion, focal deficits, seizures) – suggests intracranial extension including subdural empyema, meningitis, brain abscess, or cavernous sinus thrombosis 3, 6
• Rapid progression of erythema or swelling despite 24–36 hours of IV antibiotics – may indicate resistant organisms, abscess formation, or necrotizing infection 2, 7

Scheduled Reassessment Timing (48–72 Hours)

If the patient shows no clinical improvement after 48–72 hours of appropriate antibiotic therapy, repeat CT with contrast is mandatory to evaluate for:

• Subperiosteal or orbital abscess formation – may require surgical drainage 1, 2
• Extension into adjacent sinuses – particularly ethmoid sinusitis, the most common source in orbital cellulitis 3
• Intracranial complications – including cavernous sinus thrombosis, subdural empyema, or brain abscess 1, 3, 6
• Vascular complications – superior ophthalmic vein thrombosis or septic emboli 3, 6

The 48–72 hour window is critical because this represents the expected timeframe for clinical response to appropriate antibiotics; failure to improve by this point indicates either inadequate antimicrobial coverage, undrained purulent collection, or progression to complications requiring surgical intervention. 2, 7

High-Risk Populations Requiring Lower Threshold for Repeat Imaging

These patients warrant more aggressive imaging surveillance and should have repeat CT at the first sign of non-improvement (even before 48 hours):

• Immunocompromised patients (HIV/AIDS, chemotherapy, transplant recipients, chronic corticosteroid use) – at risk for fungal infections including mucormycosis, which progresses rapidly and has high mortality 4
• Diabetic patients – particularly those with poor glycemic control; higher risk of aggressive polymicrobial infections and mucormycosis 4
• Elderly patients – may have atypical presentations and delayed immune responses 3
• Patients with chronic sinusitis – higher baseline risk of orbital extension and abscess formation 3, 2

In immunocompromised hosts with refractory orbital cellulitis, mucormycosis must be considered as a differential diagnosis, and MRI with contrast may provide superior soft-tissue resolution compared to CT for detecting invasive fungal infection. 1, 4

Imaging Modality Selection

CT orbits/face with IV contrast is the primary imaging modality for evaluating facial cellulitis with suspected orbital involvement because it:

• Differentiates preseptal from postseptal (orbital) cellulitis 3
• Identifies abscess formation requiring drainage 1, 3
• Detects bone erosion from adjacent sinusitis 1
• Evaluates for gas in soft tissues (suggests gas-forming organisms or necrotizing infection) 8

Add MRI head and orbits with and without contrast when:

• Intracranial extension is suspected (cavernous sinus thrombosis, subdural empyema, meningitis) 1, 3, 6
• Invasive fungal infection is a concern in immunocompromised patients 1, 4
• More detailed soft-tissue assessment is needed after initial CT 1

Consider MRA or CTA if vascular complications are suspected, particularly cavernous sinus thrombosis in the setting of rapidly progressive infection or septic emboli. 1, 6

Critical Pitfalls to Avoid

• Do not delay repeat imaging when any red-flag clinical findings develop, even if the initial 48–72 hour window has not elapsed – vision-threatening and life-threatening complications can develop rapidly 3, 4, 2
• Do not rely solely on clinical examination to rule out orbital involvement; 41% of patients with preseptal cellulitis on clinical exam had postseptal involvement on CT staging 2
• Do not assume improvement based on stable erythema alone – residual inflammation can persist after bacterial eradication, but new proptosis, vision changes, or ophthalmoplegia always indicate progression 5, 3
• Do not miss odontogenic sources – obtain dental imaging if maxillary involvement is present, as dental abscesses can cause orbital cellulitis and cavernous sinus thrombosis 6
• In immunocompromised patients, do not delay antifungal coverage if mucormycosis is suspected; mortality is extremely high without prompt surgical debridement and amphotericin B 4

Surgical Consultation Triggers

Obtain urgent ophthalmology, otolaryngology, and/or neurosurgery consultation when repeat CT demonstrates:

• Any orbital or subperiosteal abscess (stage II–IV orbital cellulitis) 2
• Intracranial extension or cavernous sinus thrombosis 3, 6
• Gas in orbital tissues 8
• Clinical deterioration despite 24–36 hours of appropriate IV antibiotics 2, 7

Surgery should be considered not only when abscess is demonstrated but also if clinical deterioration occurs within 24–36 hours of adequate IV antibiotic treatment, as delayed intervention increases risk of permanent vision loss and intracranial complications. 2