Orbital cellulitis overview

# Overview
Orbital cellulitis is an inflammation of the deep, soft tissue cells surrounding the eye, posterior to the orbital septum. This inflammation can occur by means of extension of an adjacent infection, by direct inoculation through traumatic or iatrogenic pathways, or by hematogenous spread from a distant infected site. Orbital cellulitis most commonly occurs from typical bacterial infections. In some cases, mycobacteria or mycosis may be implicated. The most common underlying condition is ethmoid sinusitis. Children are more commonly affected by orbital cellulitis than adults. Orbital cellulitis has a higher incidence in the winter months and follows the seasonal patterns of sinusitis and upper respiratory tract infections. The most commonly reported pathogens are Staphylococcus aureus, Streptococcus spp. and Haemophilus influenzae. MRSA must be considered as a potential cause and is correlated with geographic prevalence. A positive history of  fever, proptosis, eyelid edema and erythema, diplopia, and painful or restricted ocular movements is highly suggestive of orbital cellulitis. Orbital cellulitis must be differentiated from various conditions which affect the eye and present similarly, such as periorbital cellulitis, cavernous sinus thrombosis, and orbital or periorbital neoplasia. Both CT and MRI of the head may be used as gold standard diagnostic imaging modalities. The most common risk factors for orbital cellulitis include acute or chronic ethmoid sinusitis, upper respiratory tract infection, and recent ocular or periocular procedures or infections. If left untreated, orbital cellulitis may result in blindness in 20% of patients and death in 17%. Serious complications can develop as a result of orbital cellulitis, such as abscess, orbital compartment syndrome, intracranial extension of infection, and septic shock. Although orbital cellulitis is an ophthalmologic emergency, the prognosis is good if prompt medical treatment is received. The mainstay of therapy for orbital cellulitis involves prompt intravenous antimicrobial therapy. Surgery may be necessary if medical therapy is ineffective, if there is intracranial extension of the disease, or in the presence of abscesses. Effective measures for the primary prevention of orbital cellulitis include prompt, appropriate, and aggressive treatment of adjacent infections.

# Historical Perspective
Orbital cellulitis first appears in the literature as early as 1882. Hypotheses regarding the etiology and management approaches were developed by various physicians and scientists. In 1937, Dr. Davis reported a review of 54 successfully treated patients, and suggested a management guideline for orbital cellulitis.

# Classification
Orbital cellulitis may be classified according to the microbial family of the offending pathogen (bacterial vs. fungal), or by the management protocol (medical vs. surgical therapy). In 1970, Chandler's classification was created to describe five groups of complications of sinusitis by invading the surrounding tissue. This system is often used to describe the extent of orbital and periorbital disease.

# Pathophysiology
Orbital cellulitis occurs secondary to microbial infiltration of the deep soft tissue cells surrounding the eye, posterior to the orbital septum. The infiltration can occur by means of extension of an adjacent infection (e.g. rhinosinusitis), by direct inoculation through traumatic or iatrogenic pathways, or by hematogenous spread from a distant infected site. Regardless of the mode of infiltration of the retroseptal orbital space, symptoms may arise due to the immune system triggering a regional or systemic acute inflammatory response.

# Causes
Orbital cellulitis occurs most commonly from typical bacterial infections. In some cases, mycobacteria or mycosis may also be implicated. By far, the most common underlying condition is ethmoid sinusitis. It has been reported as the cause in 90-98% of orbital cellulitis cases. Thus, the most commonly reported pathogens were Staphylococcus aureus, Streptococcus spp., and Haemophilus influenzae. With the rise of microbial resistance in more recent years, methicillin-resistant Staphylococcus aureus (MRSA) must be considered as a potential cause and correlated with geographic prevalence.Though some causes may be uncommon, orbital cellulitis is a medical emergency. Thus, it is pertinent to consider all possible etiologies and the most common pathogens according to the clinical scenario.

# Differentiating Orbital cellulitis from other Diseases
Orbital cellulitis must be differentiated from various conditions which affect the eye and present with similar symptoms, and include periorbital cellulitis, cavernous sinus thrombosis, and neoplasia.

# Epidemiology and Demographics
Children are more affected by orbital cellulitis than adults. In childhood, males are more likely to contract the disease than females. Orbital cellulitis has a higher incidence in the winter months and follows the seasonal patterns of sinusitis and upper respiratory tract infections.

# Risk Factors
The most common risk factors for orbital cellulitis include acute or chronic ethmoid sinusitis, pansinusitis, upper respiratory tract infection and recent ocular or periocular procedures or infections.

# Screening
There are no recommended screening guidelines for orbital cellulitis.

# Natural History, Complications, and Prognosis
If left untreated, orbital cellulitis may result in death in 17% of patients, and blindness in 20%. Complications that can develop as a result of orbital cellulitis include abscess, orbital compartment syndrome, intracranial extension of infection, and septic shock. Although orbital cellulitis is considered an ophthalmic emergency, the prognosis is good if prompt medical treatment is received. Depending on the extent of complications at the time of diagnosis, prognosis may vary. The most feared complications include septic shock, cavernous sinus thrombosis, and meningitis. These complications carry a much poorer prognosis.

# Diagnosis

## History and Symptoms
A positive history of fever, proptosis, eyelid edema and erythema, and painful or restricted ocular movements is suggestive of orbital cellulitis. Additionally, patients with orbital cellulitis often have a recent history of rhinosinusitis, upper respiratory tract infection, facial insect bite, orbital surgery or trauma, tooth abscess, or otitis media.

## Physical Examination
Patients with orbital cellulitis usually appear ill. Physical examination of patients with orbital cellulitis is usually remarkable for fever, proptosis, ophthalmoplegia, and impaired visual acuity. Patients should undergo a complete physical examination, paying particular attention to general appearance, vital signs, visual acuity, visual field, orbital positioning, ocular movmements, oropharynx, and nasopharynx examinations.

## Laboratory Findings
There are no diagnostic lab findings associated with orbital cellulitis. Some patients with orbital cellulitis may have elevated ESR, CRP, and white blood cells with a left shift. These are non-specific findings associated with infections, inflammatory conditions and some neoplasia. Blood and nasal mucosal cultures are often ordered to help guide medical therapy, though they have low positive and negative predictive values, and thus do not contribute to diagnosis of orbital cellulitis.

## X Ray
There are no diagnostic x ray findings associated with orbital cellulitis. In cases where CT scan is contraindicated, plain radiograph (x ray) is indicated prior to MRI in patients with a suspected history of metallic object ocular trauma.

## CT
Computed tomography of the orbit is the imaging modality of choice for patients with orbital cellulitis. On CT scan of the head, orbital cellulitis is characterized by hyperdensity within low density periorbital fat and generalized elevation of the periobital space. CT is also diagnostic of subperiosteal and orbital abscesses associated with orbital cellulitis.

## MRI
MRI has demonstrated equivalence to CT in diagnosing orbital disease and is also accepted as a gold standard diagnostic imaging modality. On MRI scan of the head, orbital cellulitis is characterized by hypointense signal on T1-weighted fat-suppressed images, and hyperintense signal on T2-weighted fat-suppressed images. Although an MRI scan is safer in children since there is no risk of radiation exposure, the long acquisition time and the need for prolonged sedation make CT scan the imaging modality of choice.

## Ultrasound
There are no ultrasound findings specifically associated with orbital cellulitis. Ultrasound can detect an abscess in the anterior orbit or medial orbital wall with high sensitivity. On orbital ultrasound, orbital abscess may show an anechoic mass with low internal reflectivity.

## Other Imaging Findings
There are no other diagnostic imaging findings associated with orbital cellulitis.

## Other Diagnostic Studies
There are no other diagnostic studies associated with orbital cellulitis.

# Treatment

## Medical Therapy
Orbital cellulitis is considered an ophthalmologic emergency. The mainstay of therapy for orbital cellulitis involves prompt intravenous antimicrobial therapy with either beta-lactams or Clindamycin. Patients suspected to have MRSA-induced orbital cellulitis require more extensive antimicrobial therapy.

## Surgery
An abscess can threaten the vision or neurological status of a patient with orbital cellulitis, therefore sometimes surgical intervention is necessary. Surgery typically requires drainage of the sinuses and if a subperiosteal abscess is present in the medial orbit, drainage can be performed endoscopically. Post-operatively, patients must follow up regularly with their surgeon and remain under close observation.

## Primary Prevention
Effective measures for the primary prevention of orbital cellulitis include prompt, appropriate and aggressive treatment of adjacent infections. Cases of acute bacterial rhinosinusitis should be managed effectively.

## Secondary Prevention
Secondary Prevention strategies following orbital cellulitis include obtaining blood cultures and immediately starting aggressive empirical antimicrobial therapy, diagnostic imaging studies to monitor for abscess formation and evaluation of necessity of surgical intervention. If cultures are positive, tailor antimicrobial therapy to the pathogen.