Periorbital vs Orbital Cellulitis

Preseptal cellulitis is an inflammation of the tissues localized anterior to the orbital septum.

The orbital septum is a fibrous tissue that divides the orbit contents into 2 compartments:

• preseptal (anterior to the septum)
• postseptal (posterior to the septum).

The inflammation that develops posterior to the septum is known as “orbital cellulitis.”

Both entities are caused by an infectious process.

Pathophysiology

Routes of Pathogen Inoculation:

1. Direct inoculation:
   • Eyelid trauma
   • Infected insect bites
2. Contiguous spread from adjacent structures:
   • Paranasal sinuses (especially ethmoid sinuses via lamina papyracea)
   • Chalazion or hordeolum
   • Dacryocystitis or dacryoadenitis
   • Canaliculitis
   • Impetigo, erysipelas
   • Herpes simplex/zoster lesions
   • Endophthalmitis
3. Hematogenous spread:
   • From URTI or otitis media via valveless venous systems

Venous Anatomy and Spread:

• Orbit, eyelids, and sinuses drain via superior/inferior orbital veins to the cavernous sinus
• Lack of valves → facilitates bidirectional spread
• Risk of cavernous sinus thrombosis from both preseptal and orbital infections

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Classification (Modified Chandler’s Classification)

1. Preseptal cellulitis
2. Orbital cellulitis
3. Subperiosteal abscess
4. Orbital abscess
5. Cavernous sinus thrombosis

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Etiology

Bacterial causes (most common overall):

• Gram-positive cocci:
  • Staphylococcus aureus (including trauma-related cases)
  • Staphylococcus epidermidis
  • Streptococcus pyogenes
  • Streptococcus pneumoniae (especially with sinusitis)
• Anaerobes (e.g., Clostridium) → human bite-related cases
• Haemophilus influenzae type b (Hib):
  • Historically common in children <5 yrs (now rare with vaccination)
  • Still relevant in unvaccinated patients

Viral causes:

• Adenovirus
• Herpes simplex virus (HSV)
• Varicella zoster virus (VZV)

Fungal causes:

• Consider in immunocompromised patients (e.g., mucormycosis)

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Diagnosis

General symptoms:

• Eyelid abscess may occur (may need I&D)
• Periorbital vs Orbital Cellulitis
• Eyelid swelling, erythema, warmth
• Low-grade fever, malaise
• Cellulitis may extend to cheek/forehead

Feature	Periorbital (Preseptal)	Orbital (Postseptal)
Location	Anterior to orbital septum	Posterior to orbital septum
Systemic features	Mild or absent	Systemically unwell, fever common
Eyelid	Unilateral swelling	More marked swelling, unilateral
Conjunctiva	Normal	Chemosis
Eye movements	Normal	Painful, restricted
Proptosis	Absent	Present
Diplopia	Absent	Present (early sign)
Optic nerve function	Normal	May show ↓ acuity, colour, visual field defects
Common causes	Trauma, hordeolum, dacryocystitis	Sinusitis (esp. ethmoid), trauma, surgery
Complications	Spread to orbit (rare)	Cavernous sinus thrombosis, vision loss, abscess

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Orbital Cellulitis is a Medical Emergency

• Requires urgent imaging (CT orbits/sinuses)
• May lead to intracranial infection, abscess, permanent vision loss
• Admit for IV antibiotics ± surgical drainage

👶 Children <4 years

• Higher risk of orbital cellulitis from posterior spread due to incomplete orbital septum
• Children <3 months: always refer to hospital

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Approach to Periorbital Cellulitis

as per eTG

Initial Assessment

• Check for orbital signs: proptosis, ophthalmoplegia, reduced visual acuity
• If unable to examine due to swelling, escalate care

Indications for IV Therapy or Hospital Referral

• Systemically unwell
• Inadequate eye exam (due to swelling or non-cooperation)
• Failure of oral therapy within 48h
• Age <3 months
• High Hib risk (e.g., incomplete vaccination)

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Antibiotic Choices for Periorbital Cellulitis

as per eTG 2025

🧑‍⚕️ Patients without sinusitis/Hib risk:

• Low MRSA risk:
  • Dicloxacillin 500 mg PO q6h (child: 12.5 mg/kg up to 500 mg)
  • Flucloxacillin 500 mg PO q6h (child: same as above)
  • OR Cefalexin 500 mg PO q6h (child: 12.5 mg/kg or 20 mg/kg q8h if poor adherence)
• Penicillin allergy:
  • Nonsevere: Cefalexin as above
  • Severe: Trimethoprim + Sulfamethoxazole 160+800 mg PO q12h (child: 4+20 mg/kg)
  • OR Clindamycin 450 mg PO q8h (child: 10 mg/kg)
• High MRSA risk:
  • TMP+SMX or Clindamycin as above

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With sinusitis or Hib risk (e.g., <5 yrs not fully vaccinated):

• Low MRSA risk:
  • Amoxicillin+clavulanate 875+125 mg PO q12h (child: 22.5+3.2 mg/kg)
  • OR Cefuroxime 500 mg PO q12h (child: 15 mg/kg)
• Severe Penicillin allergy:
  • TMP+SMX 160+800 mg PO q12h (child: as above)

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IV Therapy for Periorbital Cellulitis (when indicated)

• Low MRSA risk:
  • Flucloxacillin 2 g IV q6h (child: 50 mg/kg up to 2 g)
  • OR Cefazolin 2 g IV q8h (child: 50 mg/kg) if nonsevere penicillin allergy
• Severe allergy:
  • Vancomycin IV (dosing per renal function and guidelines)

Duration & Review

• Review within:
  • 24 hrs (IV therapy) or 48 hrs (oral therapy)
• Usual duration: 7 days (IV + oral)
• Extend if symptoms persist

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Approach to Orbital Cellulitis

Investigations

• Urgent CT orbits + sinuses
• Blood cultures
• 4-hourly visual acuity/pupil checks

Empirical IV Antibiotics

• Standard regimen:
  • Ceftriaxone 2 g IV daily + Flucloxacillin 2 g IV q6h
  • OR Cefotaxime 2 g IV q8h
• MRSA risk or severe beta-lactam allergy:
  • Add or substitute Vancomycin
  • If anaerobes suspected: add Metronidazole 500 mg IV q8h
  • For severe beta-lactam allergy: Vancomycin + Ciprofloxacin IV

📤 Step Down Oral Therapy (Total 10–14 Days)

• Amoxicillin+clavulanate 875+125 mg PO q12h
• OR Cefuroxime 500 mg PO q12h
• OR TMP+SMX 160+800 mg PO q12h (if MRSA or penicillin allergy)

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from RCH

https://www.rch.org.au/clinicalguide/guideline_index/Periorbital_and_orbital_cellulitis

antibiotic treatment

	Intravenous therapy	Oral therapy	Total duration
Orbital cellulitis	3rd generation cephalosporin Cefotaxime 50 mg/kg (max 2 g) IV 6 hourly OR Ceftriaxone 100 mg/kg (max 4 g) IV daily If suspected MRSA, add vancomycin (see link for dosing) Duration based on clinical severity and improvement. Usually at least 3-4 days, then switch to oral	Amoxicillin with clavulanic acid (doses based on amoxicillin component) 22.5 mg/kg (max 875 mg) oral bd	10–14 days
Severe periorbital cellulitis
Moderate periorbital cellulitis	Cefazolin 50 mg/kg (max 2 g) IV 8 hourly OR Ceftriaxone 50 mg/kg (max 2 g) IV daily (HITH) OR If suspected MRSA, Clindamycin 15 mg/kg (max 600 mg) IV 8 hourly  OR  oral   Duration based on clinical severity and improvement. Usually 1-2 days, then switch to oral	When improving, switch to oral antibiotics as per mild periorbital cellulitis If suspected MRSA:Clindamycin 15 mg/kg (max 600 mg) oral TDS  OR Trimethoprim/sulfamethoxazole (8/40 mg/mL) 4/20 mg/kg (max 320/1600 mg) oral BD	7–10 days
Mild periorbital cellulitis	Not applicable	Cefalexin 20 mg/kg (max 750 mg) oral TDS OR Cefuroxime 3 months – 2 years: 10 mg/kg (max 125 g), 2 – 12 years: 15 mg/kg (max 250 mg) oral BD	7-10 days

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Prognosis

• Generally good with prompt diagnosis and treatment.
• Risk of complications remains, even with early and appropriate management.

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Complications

1. Orbital Extension

• Orbital cellulitis
• Subperiosteal abscess
• Orbital abscess
• Cavernous sinus thrombosis (via valveless ophthalmic veins)

2. Central Nervous System Involvement

• Occurs secondary to orbital extension
  • Meningitis
  • Intracranial abscesses: brain, subdural, or extradural

3. Necrotizing Fasciitis

• Rare, but severe
• Typically caused by β-hemolytic Streptococcus
• Clinical features:
  • Rapidly spreading cellulitis
  • Poorly demarcated margins
  • Violaceous skin discoloration
  • Risk of necrosis and toxic shock syndrome
• Management:
  • Hospital admission
  • IV fluid resuscitation
  • IV broad-spectrum antibiotics
  • Urgent surgical debridement may be required