Orbital Cellulitis

The orbital septum is a fibrous membrane arising from the periosteum of the orbital rim at the arcus marginalis. Superiorly it inserts into the levator aponeurosis, and inferiorly it inserts into the tarsal plate. It forms the key anatomical barrier separating preseptal from postseptal infection.

Chandler's classification stages orbital complications of sinusitis from preseptal inflammation to cavernous sinus thrombosis. The original 1970 Chandler classification was based on clinical staging; modern practice applies the same staging together with CT findings for localization of abscess and surgical planning.

1. Sinusitis: Most Common Source

Paranasal sinusitis accounts for the majority of orbital cellulitis cases. The ethmoid sinus is the most common source, especially in children, because the thin lamina papyracea allows direct spread into the orbit.

2. Other Sources

• Contiguous spread from facial cellulitis, dacryocystitis, dental infection, panophthalmitis, or infected eyelid/orbital wounds.
• Post-traumatic infection, especially penetrating trauma or orbital fractures communicating with sinuses.
• Foreign body implantation, particularly wood or vegetable matter, which increases the risk of fungal infection.
• Post-operative infection after orbital, sinus, or eyelid surgery.
• Haematogenous spread during systemic sepsis, especially in neonates and immunocompromised patients.

Causative Organisms

Preseptal vs Orbital Cellulitis

Symptoms

• Painful, red, swollen eyelids; the eye may be difficult to open.
• Severe orbital ache, worsened by eye movement.
• Blurred vision, diplopia, or reduced colour vision if optic nerve function is threatened.
• Fever, malaise, headache and systemic toxicity.
• History of sinusitis, URTI, dental infection, trauma, surgery, diabetes, or immunosuppression.

Signs

• Proptosis: axial if diffuse or posterior; directional if due to a localized subperiosteal abscess, such as medial abscess causing lateral displacement.
• Chemosis with conjunctival injection and oedema.
• Restricted painful EOM, either in all directions due to inflammatory oedema or in a pattern related to abscess site.
• RAPD and reduced VA indicate optic nerve compromise and require urgent intervention.
• Raised IOP from proptosis and venous congestion.
• Lid erythema, warmth, tenderness, and tense orbital swelling.

1. CT Orbit and Paranasal Sinuses with Contrast

CT orbit and paranasal sinuses with contrast is the investigation of choice in suspected orbital cellulitis when orbital signs, abscess, trauma, poor response, or complications are suspected. It should include axial and coronal sections.

• Differentiates preseptal from postseptal disease.
• Shows postseptal fat stranding, extraocular muscle thickening, abscess formation, bony erosion, foreign body, and extent of sinus disease.
• Abscess appears as a hypodense collection with rim enhancement.
• Subperiosteal abscess is often a biconvex or lenticular hypodense collection, most commonly along the medial orbital wall.
• Defines anatomy and guides surgical approach.

2. MRI Orbit / Brain and MR Venography

• MRI is superior for soft tissue detail, optic nerve involvement, orbital apex disease, intracranial extension, and cavernous sinus thrombosis.
• T1 with gadolinium may show ring-enhancing abscess; T2 shows high signal in oedematous tissue.
• MRI/MRV is the gold-standard imaging approach for cavernous sinus thrombosis, showing loss of flow void and venous filling defect.

3. Blood Tests

• Full blood count: leukocytosis with neutrophilia.
• CRP and ESR: elevated and useful for response monitoring.
• Blood cultures before antibiotics, though yield is modest.
• Renal function and LFTs before IV antibiotics or antifungals.
• Blood glucose and ketones when diabetes or mucormycosis is suspected.

4. Microbiological Sampling

• Nasal swab or nasal discharge culture.
• Pus culture from abscess drainage is critical for targeted therapy.
• Lumbar puncture only when meningitis is suspected and after appropriate neuroimaging if raised ICP is a concern.

5. Ophthalmic Assessment

• Visual acuity and colour vision.
• Pupil examination for RAPD.
• Ocular motility and diplopia charting where feasible.
• IOP measurement.
• Fundoscopy for papilloedema, optic disc oedema, choroidal folds, vascular occlusion, or retinal complications.

All patients with orbital cellulitis require admission and urgent multidisciplinary care involving ophthalmology, ENT, paediatrics or medicine, microbiology, and neurosurgery when intracranial spread is suspected.

A. Initial Measures

• Admit and start IV broad-spectrum antibiotics after blood cultures if this does not delay treatment.
• Baseline and serial monitoring of VA, pupils, colour vision, EOM, proptosis, IOP, temperature, CRP, and systemic status.
• Urgent CT orbit and sinuses with contrast when orbital signs are present or abscess is suspected.
• Treat associated sinusitis with ENT input.
• Protect cornea if exposure keratopathy is present.

B. Empirical Medical Treatment

C. Adjunctive Measures

• Analgesics, antipyretics, fluids, and sepsis management where required.
• Nasal saline irrigation and topical nasal decongestants to improve sinus drainage.
• Steroids are controversial: they may reduce oedema in selected bacterial Chandler II-III cases after antibiotics have started, but must be avoided in suspected fungal infection.

D. Indications for Surgical Drainage

• Orbital abscess or significant subperiosteal abscess on imaging.
• No clinical improvement after 24-48 hours of adequate IV antibiotics.
• Visual compromise: reduced VA, RAPD, impaired colour vision, optic nerve compression, or worsening ophthalmoplegia.
• Large abscess, commonly >10 mm, or enlarging abscess on repeat imaging.
• Non-medial abscess, especially superior, lateral, inferior, or posterior collection.
• Age >9 years, because older children behave more like adults and are more likely to need drainage.
• Fungal infection, foreign body, dental source, or intracranial extension.

E. Surgical Approaches

Management Algorithm

• Suspected orbital cellulitis: admit, CT orbit/PNS with contrast, FBC, CRP, blood cultures, glucose, and full ophthalmic assessment.
• Chandler I-II without abscess: IV antibiotics, close monitoring every 6-8 hours, repeat CT in 24-48 hours if not improving.
• Chandler III subperiosteal abscess: small medial abscess in child <9 years without visual compromise may receive initial IV antibiotics and close review; age >9 years, non-medial abscess, >10 mm abscess, visual threat, or deterioration requires drainage.
• Chandler IV orbital abscess: urgent surgical drainage plus IV antibiotics.
• Chandler V cavernous sinus thrombosis: ICU, broad-spectrum IV antibiotics, LMWH anticoagulation, MRI/MRV, ENT/neurosurgery involvement.

Ocular Complications

• Visual loss from central retinal artery occlusion, central retinal vein occlusion, ischaemic optic neuropathy, or compressive optic neuropathy.
• Exposure keratopathy and corneal ulceration due to severe proptosis.
• Raised IOP and secondary glaucoma.
• Exudative retinal detachment.
• Panophthalmitis in severe delayed disease.

Intracranial Complications

• Cavernous sinus thrombosis: bilateral chemosis/proptosis, high septic fever, headache, meningism, altered sensorium, and ophthalmoplegia.
• Meningitis due to direct or haematogenous spread.
• Subdural empyema, extradural abscess, brain abscess, or frontal lobe abscess.

Systemic Complications

• Septicaemia and septic shock.
• Osteomyelitis of orbital walls or frontal bone.
• Pott's puffy tumour: frontal osteomyelitis with subperiosteal abscess.

Cavernous Sinus Thrombosis: Exam Table

Rhino-Orbital Mucormycosis

In diabetic ketoacidosis or immunocompromised patients, Mucorales such as Rhizopus, Mucor, and Absidia cause angioinvasive fungal infection. It is a separate emergency entity and should be suspected when orbital cellulitis is associated with necrosis, black eschar, rapid visual loss, or orbital apex involvement.

• Black eschar on nasal mucosa or palate is a key clue.
• Rapid orbital apex involvement may cause sudden blindness.
• Cavernous sinus involvement may occur early.
• Treatment is urgent control of diabetes/DKA, IV liposomal amphotericin B, aggressive surgical debridement of necrotic tissue, and possible orbital exenteration.
• Steroids must be avoided when fungal infection is suspected.

Paediatric Orbital Cellulitis

• Children <9 years with small medial subperiosteal abscess, no RAPD, normal vision, and good response to antibiotics may be managed medically with very close monitoring.
• Children >9 years behave more like adults and have a higher likelihood of polymicrobial infection and need for drainage.
• Empirical antibiotic choice should reflect local vaccination status; Hib is now uncommon in routinely Hib-vaccinated populations but remains a historical PYQ organism.