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While the terms periorbital (preseptal) and orbital (postseptal) cellulitis sound similar, their pathogenesis, management, and complications are quite different. Periorbital infections refer to infections located anterior to the orbital septum, while orbital infections are infections located posteriorly.
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Periorbital infections occur more frequently than orbital infections. Both infections are most commonly bacterial in origin and represent infections of the eyelid and the area surrounding the orbit. In general, these infections are caused by contiguous spread from adjacent infected structures, local trauma, or bacteremia. Noninfectious etiologies of periorbital and orbital cellulitis include inflammatory, allergic, endocrinologic, and neoplastic diseases.1
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Prior to the advent of the Haemophilus influenzae type b conjugate vaccine in 1985, the majority of periorbital cellulitis in children was secondary to bacteremia from H. influenzae type b, which caused approximately 80% of the cases.2 The introduction of the H. influenzae type b vaccine reduced pediatric cases of periorbital and orbital cellulitis by 59%.3 Today, the most common cause of periorbital cellulitis is adjacent spread from infected neighboring structures, including skin, conjunctiva, eyelids, sinuses, respiratory tract, and teeth.4 Other causes of periorbital cellulitis include blunt or penetrating trauma, viral infections such as adenovirus or Epstein–Barr virus, and bacteremia. In immunocompromised hosts, fungal etiologies, such as aspergillosis and phycomycosis, should be considered.4,5
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Orbital cellulitis is an inflammation of the orbital structures, which is most commonly a complication of sinusitis, and, in more than 90% of cases, is ethmoidal in origin.5 Other causes of orbital cellulitis include blunt or penetrating trauma, bacteremia, extension from infected adjacent structures such as dacryocystitis, or severe odontogenic infections.1,5 Because sinusitis is more common in older than in younger children, orbital cellulitis tends to be seen more commonly in older children, and the occurrence tends to peak in the winter months when sinusitis is more prevalent (Table 22–1).6
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