Fig. 25. A 6-year-old boy with a clinical diagnosis of left orbital cellulitis. A medial sub-periosteal abscess is present, secondary to a seemingly minor infection of the anterior ethmoid complex. (Harris GJ, Beatty RL: Acute proptosis in childhood. In Linberg JV [ed]: Oculoplastic and Orbital Emergencies. Norwalk, CT: Appleton & Lange, 1989:100.)