Orbital Cellulitis

Background: the orbital septum

The orbital septum is a fibrous sheet which is attached peripherally around the margin of the orbit where it is continuous with the periosteum. Centrally, it fuses into the tarsal plates. It effectively separates the eyelids from the contents of the orbital cavity.

Orbital cellulitis versus preseptal cellulitis

Orbital cellulitis is an extremely serious (potentially life-threatening) but uncommon condition characterised by infection of the soft tissues behind the orbital septum. Preseptal cellulitis refers to the much more common and far less serious infection anterior to the orbital septum. Very occasionally, preseptal cellulitis progresses to orbital cellulitis. Orbital cellulitis and preseptal cellulitis are not terms that can be used interchangeably.

Orbital cellulitis: pathophysiology

This often arises in one of three situations:¹

• As an extension of an infection from the periorbital structures (usually the paranasal sinuses: ethmoid sinusitis is the most common causative factor) and also from the face, the globe, the lacrimal sac and dental infection (via an intermediary maxillary sinusitis).
• As a result of direct inoculation of the orbit from trauma (accidental or surgical). Post-traumatic orbital cellulitis tends to develop within 72h of the injury.
• Due to haematogenous spread from distant bacteremia.

Occasionally, it may occur as an extension of preseptal cellulitis. The pathogens most commonly involved are the aerobic, non-spore forming bacteria - Strep. pneumoniae, Staph. aureus, Strep. pyogenes and H. influenzae (the latter classically found in children² although there has been a significant decline in this organism over the past couple of decades³). Mucormycosis associated with patients who have diabetic ketoacidosis or immunosuppression is also described. This very rare and rapidly spreading infection is caused by fungi is aggressive and often fatal.⁴ Orbital cellulitis may be complicated by spread to adjacent structures and to the central nervous system.

Preseptal cellulitis: pathophysiology

This may also arise in one of three situations:⁴

• As a result of local skin trauma such as lacerations and insect bites.
• Due to spread from local infection such as dacrocystitis and paranasal sinuses.
• Spread from distant infections such as those outlined above as well as from the upper respiratory tract.⁵

The most common pathogenic organisms are Staph. aureus, Staph. epidermidis, the Streptococcus species and anaerobes. In this day and age of bioterrorist threat, it is worth noting that both anthrax and smallpox cause preseptal cellulitis⁶ but clearly, in this situation, patients will present with a host of other problems. The orbital septum limits spread to associated structures and notably to the central nervous system.⁵

• Orbital cellulitis is much less common than preseptal cellulitis although data relating to the exact incidence is scant.
• Both conditions occur more commonly in the winter months owing to the increased incidence of paranasal sinus infection.
• There is no predilection for gender or race.
• Both conditions are more common in children: orbital cellulitis more frequently affects 7-12 year olds whereas preseptal cellulitis occurs at younger ages (80% of patients are under 10 years of age and most are younger than 5⁶ with a mean age of 21 months⁷).

• Orbital / preseptal cellulitis
• Necrotizing fasciitis
• Chalazion
• Allergic lid swelling
• Severe viral conjunctivitis
• Cavernous sinus thrombosis
• Erysipelas
• Other orbital conditions e.g. thyroid eye disease, orbital tumours / pseudotumours, orbital vasculitis
• Other conditions e.g. insect bite, angioedema, maxillary osteomyelitis

• Diagnosis is usually made based on the clinical findings and investigations are aimed at identifying the root cause of the infection - particularly in the case of orbital cellulitis. Investigations are carried out in the hospital setting.
• A full blood count frequently shows a leucocytosis (>15,000 X10⁶) but blood cultures are frequently negative in adults. In children < 7 or 8 years of age, Strep. pneumoniae and H. influenzae may be found.
• Any discharge from skin breaks should be swabbed and sent to microbiology. Throat swabs and samples of nasal secretions may also help diagnosis.
• CT remains the gold standard imaging modality, carried out to identify any subperiosteal abscesses, paranasal sinusitis or cavernous sinus thrombosis (all needing multi-speciality input). It is also valuable in assessing trauma cases where there may be concerns about a retained orbital or intraocular foreign body.

Orbital infections fall into one of five categories:

• Stage I - preseptal cellulitis
• Stage II - orbital cellulitis
• Stage III - subperiosteal abscess (which may arise from orbital cellulitis or paranasal sinusitis)
• Stage IV - orbital abscess (a complication of orbital cellulitis)
• Stage V - cavernous sinus thrombosis and infection (the cavernous sinus drains venous blood from both eyes)

Preseptal cellulitis^8,4

• Adults: 250(qds) - 500(tds)mg oral co-amoxiclav depending on severity of infection.
• Children: 20-40mg/kg/day oral co-amoxiclav over 24h in three divided doses.
• Lid abscesses should be drained.⁶

Clinical improvement should occur over 24-48 hours. Refer if patient is systemically unwell, if there is doubt over the diagnosis, if the patient is not responding to treatment or if drainage of a lid abscess is required. It is prudent to refer all children. Hospital management may involve intravenous therapy and further investigation to confirm that this is indeed a simple preseptal cellulitis and that there are no unusual organisms involved. ENT will be involved if sinusitis is found.

Orbital cellulitis

• Hospital admission under the joint care of the ophthalmologists and the ENT surgeons is mandatory.² (Prior to the advent of antibiotics, orbital cellulitis had a mortality rate of 17% and 20% of the survivors were blind in the affected eye.¹)
• These patients will have a full set of investigations (see above).
• Intramuscular - or more commonly - intravenous antibiotics are used (e.g. ceftazidine 1gm tds) in addition to oral metronidazole (500mg tds).⁴
• Clindamycin plus a quinolone such as ciprofloxacin are used where there is penicillin sensitivity.⁹ Vancomycin is also an alternative.
• Optic nerve function is monitored every 4 hours (pupillary reactions, visual acuity, colour vision and light brightness appreciation).
• Treatment may be modified according to microbiology results and lasts for 7-10 days.
• Surgery is indicated where there is CT evidence of an orbital collection, where there is no response to antibiotic treatment, where visual acuity decreases and where there is an atypical picture which may warrant a diagnostic biopsy. Surgery often concurrently warrants drainage of infected sinuses.⁴

Preseptal cellulitis

• Progression to stage II and beyond of orbital infections.
• Unusually, lagophthalmos, lid abscess, cicatricial ectropion and lid necrosis may also be seen in these patients.¹⁰

Orbital cellulitis⁴

• Ocular: exposure keratopathy (which can lead to visual loss through permanent damage to the cornea), raised intraocular pressure, central retinal artery or vein occlusion, endophthalmitis, optic neuropathy.
• Orbital abscess: more often associated with post-traumatic orbital cellulitis. Blindness can occur through direct extension of the infection to the optic nerve.¹
• Subperiosteal abscess: usually located along the medial orbital wall. This may progress intracranially.
• Intracranial (rare): meningitis (~2%), brain abscess (~1%), cavernous sinus thrombosis (which itself can lead to spread to the brain or affect the pituitary gland). The latter is very rare in developed countries and is associated with a mortality rate of >50%.¹

Preseptal cellulitis

Prompt diagnosis and treatment should result in an uncomplicated course and full recovery.^6,10

Orbital cellulitis

Early recognition and appropriate treatment should carry a good prognosis, particularly in the absence of complications.

Preseptal cellulitis

Prophylactic antibiotics are prudent in the management of surgical and accidental trauma to the lid. Chloramphenicol ointment is a good first choice, applied qds to the clean wound for a week. Traumatic lid laceration also benefits from a review a 48-72h down the line to help identify any emerging preseptal cellulitis early.

Orbital cellulitis

There is no definitive preventative management other than the optimal treatment of any precipitative factors such as sinusitis.