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]

Branch 1 — classification and pathophysiology

Examiner: Walk me through the Chandler classification. [2]

Candidate: The Chandler classification describes five stages of orbital complications of sinusitis of increasing severity. Stage 1 is inflammatory oedema, corresponding to preseptal cellulitis. Stage 2 is orbital cellulitis — infiltration of the orbital fat posterior to the septum without a discrete abscess. Stage 3 is subperiosteal abscess, a collection between the periosteum and the orbital wall. Stage 4 is orbital abscess, a collection within the orbital fat itself. Stage 5 is cavernous sinus thrombosis, via the valveless ophthalmic veins. The stages are a continuum, and a child may present at any stage. [2]

Examiner: Why does sinusitis cause orbital cellulitis so readily in children? [1]

Candidate: The ethmoid sinuses are present at birth and sit immediately medial to the orbit, separated only by the lamina papyracea, a paper-thin and often dehiscent bony wall. Ethmoid sinusitis can erode or spread through this barrier directly into the orbit. Once infection crosses it, the inflamed orbital fat raises intraorbital pressure, restricting the extraocular muscles and compressing the venous and lymphatic drainage. That is why ethmoiditis is the dominant sinogenic source of orbital cellulitis in children. [1] [2]

Branch 2 — investigations and imaging

Examiner: What investigations will you do, and when will you image? [6]

Candidate: I would take blood cultures and inflammatory markers before antibiotics, though blood cultures are often negative. The key investigation is contrast-enhanced CT of the orbits and paranasal sinuses, which I would obtain now because this child has orbital signs. CT defines the sinus source, looks for a subperiosteal or orbital abscess and its extent, and reveals intracranial complications such as epidural or subdural empyema. I would not delay intravenous antibiotics while waiting for imaging. MRI is reserved for suspected intracranial or cavernous sinus involvement where CT is equivocal. [6] [1]

Examiner: What organisms are you covering? [1]

Candidate: The dominant organisms in paediatric orbital cellulitis are Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae and the Streptococcus anginosus group, which is particularly common in subperiosteal abscesses. Anaerobes contribute when dental disease or chronic sinusitis is the source, and community-acquired MRSA is a consideration where locally prevalent. Haemophilus influenzae type b is now rare in immunised children but must be considered in an unvaccinated child. I would send pus from any drained abscess for Gram stain, culture and susceptibility. [1] [8]

Branch 3 — treatment and the surgical decision

Examiner: What is your intravenous antibiotic regimen? [8]

Candidate: I would give intravenous ceftriaxone 50 mg per kilogram (maximum 2 g) once daily plus flucloxacillin 25 to 50 mg per kilogram (maximum 2 g) every six hours, covering the streptococci and staphylococci that dominate paediatric orbital disease. I would add metronidazole 7.5 mg per kilogram (maximum 400 mg) every eight hours for anaerobic cover if dental disease or chronic sinusitis is suspected, and vancomycin or clindamycin if MRSA is a concern. I would de-escalate when culture and susceptibility results return. [8]

Examiner: The CT shows a medial subperiosteal abscess. When do you operate, and when can you trial medical therapy? [7]

Candidate: The age-based criteria guide this. A medial subperiosteal abscess in a child under nine years with normal vision may be given a trial of intravenous antibiotics with close monitoring, because many resolve without surgery. The indications for surgical drainage are any visual compromise, a non-medial or large abscess, failure to improve after 48 hours of intravenous antibiotics, intracranial extension, and generally age nine years or older. This child is five years old but has visual compromise — reduced acuity and a relative afferent pupillary defect — which is an absolute indication for urgent surgical drainage regardless of the favourable age and medial site. [7] [8]

Branch 4 — complications and a sick child

Examiner: What are the complications of orbital cellulitis? [1]

Candidate: The feared complications are optic neuropathy and permanent visual loss from raised intraorbital pressure or direct optic nerve infection; cavernous sinus thrombosis presenting with bilateral orbital signs, cranial nerve palsies and systemic toxicity; and intracranial extension producing epidural or subdural empyema, brain abscess or meningitis. Each carries significant morbidity, and the intracranial complications carry the highest mortality. The defence against each is prompt recognition, early intravenous antibiotics, timely imaging and surgical drainage of a threatening abscess. [1] [2]

Examiner: What if the child deteriorates with bilateral signs and cranial nerve palsies? [1]

Candidate: That picture suggests septic cavernous sinus thrombosis, the Chandler stage 5 extreme, caused by spread through the valveless ophthalmic veins. I would admit to intensive care, give broad-spectrum intravenous antibiotics including MRSA and anaerobic cover, obtain urgent imaging of the cavernous sinus and intracranial structures, and involve neurology, ophthalmology, ENT and infectious diseases. The mortality remains substantial despite modern treatment, so this is an emergency of the highest order. [1] [2]

Wrap

Examiner: Summarise the periorbital-cellulitis stance in one sentence. [3]

Candidate: The orbital septum is the line: a well child with lid swelling, normal eye movements and normal vision has preseptal cellulitis and oral antibiotics with a safety-net, while a child with any orbital sign — proptosis, ophthalmoplegia, pain on movement, visual change or an abnormal pupil — has orbital cellulitis and needs admission, intravenous ceftriaxone plus flucloxacillin, contrast CT, urgent ophthalmology and ENT referral, and surgical drainage for the abscess that fails medical therapy or threatens vision, because the one child you treat late is the one who loses sight or dies. [3] [8]