Orbital cellulitis is defined as a serious infection that involves the muscle and fat located within the orbit. It is also sometimes referred to as postseptal cellulitis. Orbital cellulitis does not involve the globe itself. Although orbital cellulitis can occur at any age, it is more common in the pediatric population.The causative organisms of orbital cellulitis are commonly bacterial but can also be polymicrobial, often including aerobic and anaerobic bacteria and even fungal or mycobacteria. The most common bacterial organisms causing orbital cellulitis are Staphylococcus aureus and Streptococci species. Rare cases of orbital cellulitis caused by non-spore-forming anaerobes Aeromonas hydrophila, Pseudomonas aeruginosa, and Eikenella corrodens have also been reported. Fungal pathogens causing invasive orbital cellulitis include Mucorales which causes mucormycosis and Aspergillus which can cause life-threatening invasive orbital infections. In immunocompromised patients with orbital cellulitis, mucormycosis and invasive aspergillosis should be considered as the cause of orbital cellulitis. Mucormycosis affects patients with diabetic ketoacidosis as well as the patients with renal acidosis. Aspergillus infection of the orbit occurs in patients with severe neutropenia or other immune deficiencies, such as HIV infection. Other rare reported cause of orbital cellulitis is mycobacteria, especially Mycobacterium tuberculosis.
Orbital cellulitis is primarily diagnosed clinically by objective findings on physical examination combined with presenting signs and symptoms. The most important distinguishing feature of orbital cellulitis is the presence of ophthalmoplegia, the presence of pain with eye movement, and/or proptosis. Orbital cellulitis also typically cause eyelid swelling with or without erythema; however, these findings are also seen in another less serious condition called preseptal cellulitis. The diagnosis of orbital cellulitis can be confirmed by imaging modalities such as Computed Tomography (CT) and Magnetic Resonance Imaging (MRI). Due to the controversy surrounding imaging use and the risks of radiation exposure to the pediatric population, there are guidelines and recommendation in place that highlight the indications and aid in the proper use of imaging for diagnosis of orbital cellulitis.
Treatment of orbital cellulitis includes antibiotics and other supportive therapies. An ophthalmologist and otolaryngologist should also be consulted for proper examination and because, in some cases, surgery may be required. Without prompt diagnosis and proper treatment, the infection of the orbit can progress and extend to the adjacent anatomical locations and result in serious complications. Those complications include loss of vision, subperiosteal abscess, orbital abscess, and intracranial extension of the infection. The choice of antibiotics is broad spectrum regimens aimed at covering for organisms such as S. aureus (including methicillin-resistant S. aureus [MRSA]), Streptococcus pneumoniae, other Streptococci, as well as gram-negative bacilli. The antibiotic regimen should also include coverage for anaerobes when an intracranial extension is suspected. Antifungals are indicated only when a fungal infection is suspected in the appropriate clinical setting. Further details on specific antibiotics will be explained in the diagnosis section. Analgesics such as NSAIDs and acetaminophen can be used alone or in combination to achieve effective pain control in patients with orbital cellulitis.
The most common cause of orbital cellulitis is bacterial rhinosinusitis. Other potential causes include:
Orbital cellulitis is commonly seen in young children. It is seen less in older children and adults.
Orbital cellulitis is a rare complication of bacterial rhinosinusitis. However, in most cases of orbital cellulitis, rhinosinusitis is the source of infection. Data show that in up to 86% to 98% of cases of orbital cellulitis, there is coexisting rhinosinusitis present. Moreover, pansinusitis and ethmoid sinusitis are the forms of rhinosinusitis that most likely to lead to orbital cellulitis.
The best indicators of orbital cellulitis is a pain with eye movements, proptosis, and ophthalmoplegia with diplopia. Chemosis (conjunctival swelling) is more commonly present in orbital cellulitis; however, it may also be seen occasionally in severe cases of preseptal cellulitis. Fever and peripheral leukocytosis with a predominance of neutrophils are also seen in orbital cellulitis. Eyelid erythema may or may not be present.
The diagnosis of orbital cellulitis should always begin with a physical exam looking for clinical findings of orbital cellulitis but also for its serious complications. It is important that an ophthalmologist evaluate a patient with suspected orbital cellulitis for extraocular movements, visual acuity, and to assess for proptosis. In addition, an otolaryngologist should be consulted for evaluation of patients with extensive rhinosinusitis.
Although low yield, it is recommended to obtain blood cultures for common bacterial pathogens and, depending on the circumstances, fungi and mycobacteria from patients with suspected orbital cellulitis prior to the administration of antibiotics.
Two main imaging tools are available such as a CT and MRI to aid in the diagnosis of orbital cellulitis. MRI has been found to be superior to CT scan because it can help in following soft tissue disease progression. However, due to lack of availability of MRI, CT scanning is more commonly used. Other specific imaging modalities such as MRI or CT venography are used when complications of orbital cellulitis are suspected. Based on the studies and guidelines it is recommended that patients with suspected orbital cellulitis with any of the following features undergo a contrast-enhanced CT scan of the orbits and sinuses:
Findings on Imaging
Common CT findings in orbital cellulitis are inflammation of extraocular muscles, fat stranding, and anterior displacement of the globe, although this may be subtle. Evidence of rhinosinusitis, with the most intense, is commonly seen in ethmoid sinuses. Complications of orbital cellulitis, for example, subperiosteal abscesses and orbital abscesses appear as low-density collections on CT scan.
Uncomplicated orbital cellulitis can be treated with antibiotics alone. Treatment regimens are usually empiric and designed to address the most common pathogens as described above because reliable culture results are difficult to obtain in the absence of surgical intervention. For patients with uncomplicated orbital cellulitis, it is suggested that antibiotics be continued until all signs of orbital cellulitis have resolved. The duration of antibiotic therapy ranges from a total of at least 2 to 3 weeks. For patients with severe ethmoid sinusitis and bony destruction of the sinus, a longer period, at least 4 weeks is recommended.
Appropriate antibiotic regimens for empiric treatment in patients with normal renal function include:
Intravenous (IV) Therapy
For MRSA coverage
Plus one of the following:
Should be added to include coverage for anaerobes.
Other agents that cover for MRSA infection are daptomycin, linezolid, and telavancin; however, there is little experience using them for orbital or intracranial infections. In the absence of a contraindication such an allergy, vancomycin is the preferred agent for MRSA coverage of orbital cellulitis. Linezolid is not recommended for children with CNS infections as its concentrations in the CNS have been inconsistent in children.
In case of allergy to penicillins and/or cephalosporins, treatment with a combination of vancomycin plus:
There are no controlled trials to define the ideal duration of antimicrobial therapy in orbital cellulitis or when to switch to oral treatment from intravenous. For uncomplicated orbital cellulitis with good response to IV antibiotics, it is reasonable to switch to oral therapy. If patient remains afebrile and the eyelid and orbital findings have begun to resolve substantially, which usually takes three to five days then switching to oral antibiotics is warranted. If definitive culture data are available, oral therapy should be directed against the infecting organisms. When there are no definitive culture data, appropriate empiric oral regimens include the following:
Clindamycin or Trimethoprim-Sulfamethoxazole
Plus one of the following:
Surgery is almost always indicated in patients with intracranial extension of the infection. Other indications for surgery are poor or failure to respond to antibiotic therapy, worsening visual acuity or pupillary changes, or evidence of an abscess, especially a large abscess, greater than 10 mm in diameter. Smaller abscesses can be followed clinically and with repeat imaging unless impairment of vision is a concern. If either the clinical findings or CT scan show no improvement within 24 to 48 hours, surgical drainage is usually indicated. Surgery may also be indicated to obtain culture material, for example, in patients with suspected fungal or mycobacterial infection of the orbit. External approaches (through the orbit) and endoscopic transcaruncular surgery can be employed.
The outcomes of orbital cellulitis entirely depend on whether complications are present. For the most part, patients with orbital cellulitis respond quickly and completely to appropriate antibiotic therapy. Serious complications such as cavernous sinus thrombosis, intracranial extension, and vision loss can lead to permanent sequelae. Death is a rare but possible sequela of the complications of the orbital cellulitis.
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