A swollen right eye in a child

Short answer

Periorbital (preseptal) or orbital (post-septal) cellulitis.

Long answer

The terminology used in the literature is often ambiguous, with the terms “periorbital” and “preseptal” cellulitis used interchangeably. Similarly, the terms “orbital” cellulitis and “post-septal” cellulitis are also used interchangeably.

The orbital septum is a tough fibrous membrane that forms the scaffold for the eyelids. It also provides a barrier to infection between the superficial tissues of the face and the deep tissues within the orbits.1 2 Infection superficial to this layer (preseptal) is termed periorbital cellulitis, whereas infection deep to the orbital septum (post-septal) is termed orbital cellulitis.

Short answer

Infection of the paranasal sinuses (most commonly ethmoid sinusitis). Causative organisms tend to reflect the underlying involvement of sinus disease, with Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and Haemophilus species most commonly being cultured.3

Long answer

Periorbital and orbital cellulitis can have a sinugenic or non-sinugenic cause. Given the history of coryzal symptoms, this patient’s infection probably originated from the paranasal sinuses (maxillary, ethmoid, frontal, or sphenoid sinusitis).

Anatomically, the ethmoid sinuses lie directly medial to the orbits and are separated from the orbital cavities by a ‘paper thin’ layer of bone called the lamina papyracea. This makes the orbital cavities vulnerable to direct spread of infection from the nose.1 2

Non-sinugenic causes of infection are less common but …