Orbital cellulitis

Orbital cellulitis is a completely different disease from periorbital cellulitis and has a completely different pathogenesis. It is no trivial problem and in the pre-antibiotic era the mortality rate was 17% and 20% of the survivors were blind in the affected eye. The disease starts in the ethmoid sinus and the infection spreads into the subperiosteal lining of the orbit through the ethmoid bone.

18.	This bone (see SLIDE 18) is also called the lamina papyracea because of its thinness and because it is perforated by several blood vessels. This combination allows ready egress of inflammation from the ethmoid sinus. The orbital septum is an extension of the periosteum of the frontal bone and...
19.	extends into the eye lid (SLIDE 19) attaching to the superior portion of the tarsal plate (shown in blue). The orbital septum forms a sturdy barrier to spread of orbital infection from posteriorly to anteriorly, or anteriorly to posteriorly. Only if the orbital septum is perforated, as might occur in a sharp injury, will infection spread between these two completely separate compartments.
20.	Because of its firm attachment to the upper edge of the frontal bone, infection beginning posteriorly is limited by the orbital septum and this can be used clinically (see SLIDE 20), where a sharp demarcation line is visible just below the brow.
21-22.	Even in severe orbital cellulitis (see SLIDE 21-22) a sharp demarcation line, corresponding to the periosteal attachment of the frontal bone is clearly visible. These children tend to be ill and all have a significant fever, significant leucocytosis, and all will have evidence of sinusitis, particularly the ethmoid sinus on the affected side.
23.	In the early stages the eye may be completely normal with swelling and induration confined to the upper and/or lower lid as can be ssen on SLIDE 23.
24.	It is not clinically possible to differentiate early orbital from early periorbital cellulitis (SLIDE 24) in the absence of an obvious external cause, as seen in periorbital cellulitis.
25.	As the infection worsens (SLIDE 25) the globe itself becomes involved with injection and chemosis (edema).
26.	Pain on eye movement, pain on touch, proptosis and extraocular muscle restriction (SLIDE 26) are extremely late signs of orbital cellulitis and cannot be used to differentiate orbital from periorbital cellulitis in the early stages.
27.	All of these patients have a significant fever (SLIDE 27) and all have a significant leucocytosis with white counts often in the 14,000 to 18,000 range.

The differential diagnosis of orbital cellulitis includes the following

Sinus x-rays may show opacification of the ethmoid, sphenoid, maxillary, or frontal sinus (which does not develop until after age seven)

32.	An ethmoiditis is often readily apparent and SLIDE 32 demonstrates a left ethmoiditis and maxillary sinusitis.
33.	While CT scan is usually unnecessary to make the diagnosis, SLIDE 33 shows a left maxillary sinusitis, and...
34.	SLIDE 34 demonstrates a left ethmoiditis and sphenoiditis.
35.	Proptosis and extraocular muscle restriction (SLIDE 35) are late complications of the problem and ...
36.	are uniformly accompanied by a sterile subperiosteal abscess (SLIDE 36) where infection has spread from the obviously infected ethmoid beneath the periosteum of the ethmoid bone. In this CT the eye is proptosed as well.
37.	The subperiosteal abscess may be quite significant as shown in this left orbit in SLIDE 37 and...
38.	may push the eye into an exodeviated position (SLIDE 38).
39.	In a different view (SLIDE 39)...
40.	it is also readily apparent why this left eye can not be adducted (SLIDE 40).

Work up of orbital cellulitis

These children require admission to hospital and treatment with intravenous antibiotics. A CBC will usually indicate an elevated white count, the eye and nasopharynx may be cultured, but blood culture offers a far greater yield of offending organisms. The most common organisms are H. influenza, streptococcus, staphylococcus or diplococcus.

These children need to be followed very closely, particularly over the first 48 hours, as they may get dramatically worse before they get better. It normally takes 36 hours for the antibiotics to generate significant improvement. Daily or even twice daily assessment of their clinical condition is indicated and includes the following:

ASSESSMENT OF ORBITAL CELLULITIS

Temperature Visual acuity in each eye separately Assessment of fundi Assessment of proptosis Assessment of extraocular muscle restriction Assessment of neurological signs

Treatment of orbital cellulitis

Currently the antibiotics of choice are

CEFOTAXIME	50 mg/kg/Q6h I/V
or
CEFTRIAXONE	50 mg/kg/Q12h I/V
combined with
CLINDAMYCIN	40 mg/kg/day I/V in 3 divided doses

In patients with known allergy to penicillin:

VANCOMYCIN	30 mg/kg/day in three divided doses to run in over 90 minutes to two hours. Blood levels should be taken after the fourth dose, and the therapeutic range is 25-30 ug/ml.
With clinical improvement after three to five days of intravenous antibiotic, the intravenous medication may be changed to:
KEFLEX	P/O 25-50 mg/kg/day in four divided doses
or
CEFUROXIME	P/O 200 mg/kg/day in four divided doses (tastes awful)
or
CEFIXIME	P/O 8 mg/kg/day in one dose (tastes yummy)

Indications for surgical drainage

Worsening of ocular or neurological status despite 72 hours of full therapy Significant sub-periosteal abscess formation, unresponsive to treatment Corneal exposure from proptosis

Complications of orbital cellulitis

Extraocular muscle palsy Corneal scarring from exposure Optic nerve damage Visual loss MENINGITIS

Cavernous sinus thrombosis Osteomyelitis of skull and orbit Cerebral abscess