Management of Orbital Cellulitis

Abstract

Orbital cellulitis is an acute infectious inflammation of the post-septal orbital tissues. This chapter outlines the medical and surgical management of bacterial orbital cellulitis. The paranasal sinus complex is the most common source of orbital bacterial infection. Over 50% of orbital cellulitis cases result from secondary extension from the paranasal sinuses. Other causes of orbital cellulitis include spread from ocular and periocular infections such as dacryoadenitis, dacryocystitis, and panophthalmitis; trauma, insect bites, or surgery; or endogenous sources in immunocompromised or septic patients. Orbital cellulitis resulting from sinusitis is believed to start with viral or allergic inflammation of the upper respiratory system. The inflammation decreases mucociliary clearance and causes obstruction of the sinus ostia. The sinus mucosa absorbs air, thereby creating negative pressure within the sinuses. Transudation occurs, creating a nutrient medium for bacteria. Aerobic and facultative organisms proliferate, and inflammatory products accumulate resulting in decreasing oxygen tension and pH. As inflammatory products are produced, sinus pressure increases, causing mucosal blood flow to decrease. A proliferation of obligate anaerobes occurs as aerobic bacteria consume the remaining oxygen. Young children are less likely to develop anaerobic conditions within their sinuses because their ratio of ostia size to sinus volume is much larger than that of adults. The sinus cavities enlarge markedly with age while the ostia remain approximately the same size. Thus, as children become adults, the decreased ratio of ostia size to total sinus volume increases the propensity for anaerobic sinus infections. The bony walls shared by the orbit and sinuses account for approximately half of the orbital surface area. Bacteria and inflammatory products from the sinuses may extend directly into the orbit through the neurovascular foramina, congenital bony dehiscences, anastomosing valveless venous channels, or compromised bony walls in cases of osteitis and necrosis secondary to sinusitis. An abscess may form in the subperiosteal area, a relatively avascular potential space. Subperiosteal abscesses most often involve the medial orbital wall, as it is the thinnest wall and is adjacent to the ethmoid sinuses.