Question: Our physicians saw a patient with an acutely swollen eyelid that prevented her from fully opening her eye. Other than her obstructed vision, she exhibited no disturbance in visual activity or ocular motility, and showed no signs of proptosis, protrusion of the eye. She was diagnosed with preseptal cellulitis. Which diagnosis codes should I use for the cellulitis and the abscess? Mississippi Subscriber Answer: You should use code 373.13 (Abscess of eyelid; furuncle of eyelid) for the patient's preseptal cellulitis. As for the abscess, you will have to choose between 373.13 and 376.01 (Orbital cellulitis; abscess of orbit) based on the location and specific characteristics of the abscess. Caused by sinus infections, orbital cellulitis involves the multiple venous channels that exist between sinuses and orbits, while preseptal cellulitis involves external soft tissues and the eyelid. Interchanging the two cellulitis codes can lead to denials, given that orbital cellulitis leads potentially to more severe conditions, including abscesses of the orbital or brain, meningitis, optic neuritis, cavernous sinus thrombosis, and blindness. Physicians distinguish between the two conditions using imaging: Preseptal cellulitis appears as inflammatory changes involving external soft tissues, while orbital cellulitis can involve three separate compartments: intraconal, extraconal and subperiosteal. Check the documented evaluation of these tests, if available, to verify which code to apply.