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Findings: Axial CT images through the orbits demonstrate abnormal soft tissue swelling over the left orbit. In addition, there is abnormal soft tissue extending post septally along the lamina papyracea, causing displacement of the medial rectus laterally. In addition, the left medial rectus muscle is asymmetrically enlarged suggesting associated edema. There is also minimal left sided proptosis.
Diagnosis: Pre and post septal orbital cellulitis.
Discussion: One of the more common childhood orbital disorders are infectious processes. Orbital infections are usually secondary to paranasal sinus infection and trauma. Clinically, patients usually present with eyelid swelling and pain. CT examination is most useful to evaluate the extent of orbital involvement as well as possible bony and intracranial extension.
Inflammatory changes of the orbit are divided into two categories (preseptal versus post septal) based on their relation to the orbital septum. Pre septal cellulitis does not affect the orbital contents. On the other hand, post septal cellulitis commonly demonstrates swelling of the extra-occular muscles, as well as displacement of extraconal fat and rectus muscle away from the orbital wall. Soft tissue planes can also be obliterated. Subperiosteal cellulitis or abscess formation is often associated with multifocal sinusitis with either direct spread through the sinus wall or thrombophlebitis. Specifically, this most commonly results from inflammatory changes involving the ethmoid air cells or frontal sinuses.
The distinction of pre septal versus post septal inflammatory changes is critical because of the much more benign course of pre septal cellulitis than post septal disease.
References:
Hopper KD, et al. CT and MR Imaging of the Pediatric Orbit.
Radiographics 1992;12:485-503.
Latchaw RE. MR and CT Imaging of the Head, Neck and Spine.
Mosby, St. Louis;1991:838-842.
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