Preseptal and orbital cellulitis — branching viva

Opening question

Examiner: Take me through this child. What is the diagnosis, and what is your frame for managing it? ^[1]

Candidate: The diagnosis is orbital cellulitis. The fever, irritability, proptosis, limited eye movement and pain on movement in a child with a recent upper-respiratory infection are the classic orbital signs indicating that infection has crossed the septum and involved the orbital contents, almost certainly spreading from ethmoid sinusitis. My frame is to recognise this as a sight- and life-threatening emergency: admit, take blood cultures, start broad-spectrum intravenous antibiotics, obtain contrast CT, refer urgently to ophthalmology and ENT, and monitor vision serially. ^{[1] [3]}

Examiner: How do you distinguish orbital cellulitis from preseptal cellulitis? ^[3]

Candidate: The orbital septum is the dividing line. Preseptal cellulitis is infection anterior to the septum in the eyelid soft tissues, usually from a local skin breach or conjunctivitis; the child is well and afebrile and there is no proptosis, no chemosis, no limitation of eye movement, no pain on movement and normal vision. Orbital cellulitis is infection posterior to the septum in the orbital contents, usually from sinusitis; the child is febrile and unwell and there are the orbital signs: proptosis, chemosis, ophthalmoplegia, pain on movement, decreased visual acuity and a relative afferent pupillary defect. The presence of any orbital sign means postseptal disease. ^{[3] [1]}