Orbital cellulitis is a bacterial infection of the soft tissues within the orbit posterior to the orbital septum (a fibrous membrane at the front of the eyelid). It is considered an ophthalmic emergency.
The severity of orbital infection is assessed using the Chandler classification (1970).
Chandler I–III
Grade I (periorbital cellulitis): Edema of the eyelids and surrounding soft tissues, limited to the area anterior to the orbital septum.
Grade II (orbital cellulitis): Spread of infection to intraorbital fat tissue, with proptosis and ophthalmoplegia.
Grade III (subperiosteal abscess): Abscess formation between the orbital periosteum and the orbital wall.
Chandler IV–V
Grade IV (orbital abscess): Abscess formation within the orbital fat, with severe proptosis and complete restriction of eye movement. Vision loss is prominent.
Grade V (cavernous sinus thrombosis): Infection spreads intracranially. The most severe type with bilateral findings and impaired consciousness.
This disease commonly occurs in children and also affects young adults. Due to the anatomical relationship around the orbit, it is closely associated with sinusitis (especially ethmoid sinusitis). Compared to adults, children have a different immune response, and infection easily spreads to the orbit through the thin lamina papyracea adjacent to the ethmoid sinus. To confirm the association with the paranasal sinuses, early imaging is recommended if suspected.
Preseptal cellulitis is an infection localized anterior to the orbital septum (eyelid side) and does not involve proptosis, ophthalmoplegia, or vision loss. Orbital cellulitis is an infection that extends posterior to the septum into the orbit, and these findings are present. CT is useful for differentiating between the two.
In a study of 9 cases of orbital cellulitis due to MRSA (methicillin-resistant Staphylococcus aureus), eyelid edema 88.9%, pain 88.9%, proptosis 66.7%, ophthalmoplegia 66.7%, and fever 55.5% were recorded. 1)
Laboratory values include a median CRP of 178 mg/L and median WBC of 17.9×10⁹/L. 1)
Vision loss is a dangerous sign indicating optic nerve compression and may require urgent intervention. However, surgical indication is not based solely on vision loss but on a comprehensive assessment of abscess size and location on CT, age, and response to antibiotic therapy. See “Standard Treatment” section for details.
Orbital cellulitis develops through three main routes.
Upper respiratory tract infection, sinusitis, facial trauma, odontogenic infection, and immunocompromised status (including HIV infection) are the main risk factors. 8)
The medial wall of the orbit (lamina papyracea) is very thin and adjacent to the ethmoid sinus. In addition, valveless veins run between the paranasal sinuses and the orbit, allowing infection to spread bidirectionally. 7) Therefore, ethmoid sinusitis can easily spread directly into the orbit.
| Test | Use/Features |
|---|---|
| CT (with contrast) | First choice. Evaluates the presence, size, and location of subperiosteal abscess. |
| MRI (STIR sequence) | Detailed evaluation of soft tissue, osteomyelitis, and intracranial lesions |
| B-scan ultrasound | Auxiliary test when radiation exposure should be avoided |
CT scan is the basic diagnostic tool, and imaging with a slice thickness of 3 mm or less including coronal views is recommended for the orbit. Contrast-enhanced CT allows identification of subperiosteal abscess and orbital abscess, as well as evaluation of associated sinusitis.
MRI (especially STIR sequence) provides excellent soft tissue contrast and can detect osteomyelitis even within 12 days of onset when CT may not. 4) It is also essential for evaluating intracranial complications (epidural abscess, brain abscess). DWI (diffusion-weighted imaging) is useful for confirming abscess formation. 1)
Diseases requiring differentiation include the following:
Orbital cellulitis is generally treated with intravenous antibiotics after hospitalization. Collaboration with an otolaryngologist is essential, and surgical drainage is performed as needed.
Initial empirical treatment is based on the following:
Transition to outpatient parenteral antibiotic therapy (OPAT) is considered after clinical stability, and switching to oral antibiotics may require a long period (up to 7 weeks). 4)
Indications for Surgery
Large abscess: Active drainage is considered for large subperiosteal abscesses (e.g., ≥20 mm).
Visual impairment: If there is decreased visual acuity or afferent pupillary defect, it may be an emergency indication.
Antibiotic resistance: If there is worsening or no improvement after appropriate antibiotic therapy.
Intracranial extension: If there is spread to epidural abscess or brain abscess.
Surgical Procedure
FESS (Functional Endoscopic Sinus Surgery): Drainage of sinusitis. Performed in 88.9% of MRSA cases. 1)
External orbital drainage: Drainage of abscess via external incision. Combined approach with endoscopic surgery is also performed. 4)
Multidisciplinary collaboration: Collaboration among otorhinolaryngology, ophthalmology, and neurosurgery is essential in severe cases. 4)
The usefulness of dexamethasone as an adjunctive therapy has been reported.
AlQahtani et al. reported a dramatic improvement in a 3-year-old patient with MRSA and Pseudomonas aeruginosa infection (subperiosteal abscess 6.6 mm) treated with ceftazidime plus clindamycin and three courses of dexamethasone 6 mg (q12h, 3 days). 6)
Heri-Kovacs et al. reported that IV dexamethasone 250 mg/day for 4 days was effective in a case of orbital cellulitis after COVID-19 vaccination without sinusitis. 5)
The use of steroids requires judgment based on individual clinical circumstances, and a standard administration protocol has not been established.
Not all SPAs require surgical drainage. If the abscess is small, visual function is preserved, and there is a good response to antibiotic therapy, conservative treatment may be attempted. However, if there is vision loss, elevated intraocular pressure, or lack of response to antibiotics, prompt surgical drainage should be considered.
The lamina papyracea, which forms the interface between the orbit and the paranasal sinuses, is a bony plate that constitutes the medial orbital wall. It is extremely thin and prone to perforation. This anatomical feature facilitates the spread of infection from ethmoid sinusitis to the orbit.
Between the paranasal sinuses and the orbit, there are valveless veins that allow infection to spread hematogenously in both directions. 7) Frontal sinusitis can also lead to direct extension to the epidural space and intracranial cavity. 4)
In a retrospective study of 9 cases by Ang et al., the median hospital stay for MRSA orbital cellulitis was 13.7 days, and 100% of cases required surgical intervention. 1) The proportion of MRSA in orbital cellulitis varies by region, rising from 14.5% to 37.5% in Taiwan. 1)
Optimization of antibiotic selection and establishment of initial treatment protocols considering PVL-producing MRSA are future challenges.
Tang et al. reported 4 cases of HOC in immunocompromised patients and emphasized that NGS can identify pathogens within 48 hours. 3)
Heri-Kovacs et al. reported a 72-year-old man who developed orbital cellulitis (5 mm proptosis, ophthalmoplegia) without sinusitis 9 days after the second dose of VeroCell (inactivated COVID vaccine). 5) It resolved within 4 days after IV dexamethasone 250 mg/day for 4 days. The pathogenesis is unknown.
Ishak et al. reported a case repeatedly treated as culture-negative “orbital cellulitis” that was ultimately found to be B-cell lymphoma. 9) In treatment-resistant or recurrent orbital cellulitis, early suspicion of tumors or granulomatous diseases and thorough examination including biopsy are essential.
