Orbital cellulitis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Tarek Nafee, M.D. [2]

Pathogenesis

Orbital cellulitis occurs secondary to microbial infiltration of the deep soft tissue cells surrounding the eye, behind the orbital septum. Damage to the cells triggers an acute inflammatory response resulting in vasodilation, increased vascular permeability, and induction of a cascade of inflammatory markers and white blood cell chemoattractants.

Extension of adjacent infection

Orbital cellulitis may spread from direct extension of an acute or chronic adjacent infection. This includes the following:
-Rhinosinusitis (Ethmoid sinusitis and pansinusitis)
-Dacryocystitis, Dacryoadenitis
-Panophthalmitis
-Infected tumour
-Otitis media
-Mucormycosis
-Dental abscess

Direct inoculation

Microbes inoculated in the retroseptal orbital space by traumatic or iatrogenic means.

Traumatic

Occur as a result of direct inoculation of the microbe due to trauma:
-Fracture
-Penetration by a foreign body

Iatrogenic

Occur as a result of direct inoculation during surgical procedures such as:
-Ocular or periocular surgeries
-Paranasal Sinus surgeries
-Other ENT surgeries

Hematogeneous Spread

Infections may seed from a distant source to the retroseptal orbital soft tissue by means of hematogeneous spread in patients with bacteremia.

Associated Conditions

sinusitis
upper respiratory tract infection
subperiosteal abscess

Microscopic Pathology

• Staphylococcus aureus, is a gram-positive bacterium which is the most common of staph infections. Staphylococcus aureus infection can spread to the orbit from the skin. Staph organisms are able to produce toxins which promote their virulence which leads to the inflammatory response seen in orbital cellulitis. Staphylococcus infections are identified by a cluster arrangement on gram stain. Staphylococcus aureus forms large yellow colonies (which is distinct from other Staph infections such as Staphylococcus epidermis which forms white colonies).

• Streptococcus pneumoniae, is also a gram-positive bacterium responsible for orbital cellulitis due to its ability to infect the sinuses (sinusitis). Strep organisms are able to determine their own virulence and can invade surrounding tissues causing an inflammatory response seen in orbital cellulitis (similar to Staphyloccoccus aureus). Streptococcal infections are identified on culture by their formation of pairs or chains. Streptococcus pneumoniae produce green (alpha) hemolysis, or partial reduction of red blood cell hemoglobin.