A 12-year-old boy is brought to the emergency room with progressive eye lid swelling and redness associated with blurring of vision for the past 24 hours. Physical examination is significant for left eye lid swelling, erythema, ptosis, and painful eye movements. A computed tomography (CT) scan of the orbit shows opacification of the paranasal sinuses with retro-orbital extension and abscess formation (Figure 18-1). He is diagnosed with orbital cellulitis and orbital abscess and he is admitted to the hospital for intravenous antibiotics, and otolaryngology and ophthalmologic evaluation. His orbital abscess is surgically drained and he completes a 3-week course of antibiotic therapy and recovers completely.

Orbital cellulitis is a serious infection of the orbit that involves the tissue located posterior to the orbital septum (postseptal cellulitis). Orbital cellulitis most commonly results as a complication of sinusitis, and should be distinguished from preseptal (periorbital) cellulitis, which involves the anterior portion of the septum (Figure 18-2).^1,2

• 
  

  Post-septal cellulitis; orbital subperiosteal abscess.

• 
  

  Orbital cellulitis is mostly a disease of children, although it can be seen at any age.

  
  
• 
  

  Most commonly occurs during the winter months because of the close association between upper respiratory viral infections, rhinosinusitis, and orbital cellulitis.

• 
  

  Orbital cellulitis in children is usually a complication of rhinosinusitis, especially ethmoidal sinusitis, which results in direct extension of the inflammation to the orbit.^1,3,4

  
  
• 
  

  The ethmoid sinuses are separated from the orbit by a thin and fenestrated bony structure called lamina papyracea. Loss of integrity of the lamina papyracea from inflammation results in orbital extension (Figure 18-1).

  
  
• 
  

  Less common pathogenic causes of orbital cellulitis include penetrating trauma to the orbit, infection of the orbit following eye surgery, and bacteremic disease.

  
  
• 
  

  The etiologic agent implicated depends on the mechanism of infection. Streptococcus pneumoniae is the most likely pathogen complicating acute sinusitis. Staphylococcus aureus, Streptococcus anginosus, and anaerobic bacteria warrant consideration when orbital cellulitis complicates chronic sinusitis. These pathogens as well as gram-negative aerobes need to be considered when the process is secondary to penetrating trauma.^1,3

  
  
• 
  

  At one time a very common pathogen, Haemophilus influenzae type b (Hib) has become a very rare cause of orbital cellulitis since the introduction of the Hib vaccine. However, this organism should always be considered as a potential cause of orbital cellulitis in unimmunized children.⁵

  
  
• 
  

  Community-acquired methicillin-resistant S aureus (CA-MRSA) is an emerging pathogen causing orbital cellulitis.^6,7

  
  
• 
  

  Fungal infection (i.e., Aspergillus or mucormycosis) is a rare but life threatening cause of orbital cellulitis, occurring exclusively in immunocompromised hosts.

• 
  

  Ethmoidal sinusitis or pansinusitis.

  
  
• 
  

  Upper respiratory tract infections.

  
  
• 
  

  Incomplete or unimmunization.

  
  
• 
  

  Eye surgery or trauma to the orbit.