Periorbital Cellulitis

Etiology

Periorbital cellulitis is commonly caused by the spread of infection of rhinosinusitis or infection after a local trauma; therefore, knowledge of the anatomy of the orbit and its surrounding structures is important in understanding the spread and cause of periorbital cellulitis. The orbit, lined by periosteum, is surrounded by paranasal sinuses: the frontal sinus is superior, the ethmoid sinus is medial, and the maxillary sinus is inferior. Acute ethmoiditis is the most common rhinosinusitis causing periorbital and orbital cellulitis. An infection stemming from the ethmoid sinus is rapidly progressive, especially because the lamina papyracea is the only border between the ethmoid sinus and the orbit. This lamina is very thin with perforations and fenestrations, called Zuckerkandl’s dehiscence, that allows passage of nerves and blood vessels. This allows the easy spread of infection from the ethmoid sinuses to the periorbital and orbital region.[5][6][7][8]

The orbital septum is a membranous sheet arising from the orbital periosteum lining; this boundary determines if the infection is periorbital (preseptal) or orbital (postseptal). Infections that are preseptal rarely result in serious complications, and some cases can lead to orbital cellulitis. A more common problem is the misdiagnosis of orbital cellulitis as periorbital cellulitis which leads to improper treatment. Also, the orbital septum does act as a barrier. However, periorbital infections can also spread via the facial venous system which has no valves, allowing easy access to the posterior spread of infection into the orbits and beyond. The superior and ophthalmic veins also drain blood directly into the cavernous sinus, which can allow spread to intracranial structures. With inadequate or improper treatment and continued spread, periorbital and orbital cellulitis can become invasive leading to ophthalmic complications such as vision impairment and blindness and intracranial complications.

The Chandler classification of orbital complications groups orbital complications based on severity to assist with determining the appropriate treatment. Although this classification is not a true continuum of disease, it is important to consider these groups when making a diagnosis, especially because of similarities in presentation. The groups are:

• Group 1 pre-septal cellulitis
• Group 2 orbital cellulitis
• Group 3 subperiosteal abscess
• Group 4 orbital abscess
• Group 5 cavernous sinus thrombosis.

Epidemiology

Periorbital cellulitis can occur at any age, but it is especially common in the pediatric population. Periorbital cellulitis is more common than orbital cellulitis. Some studies suggest a mortality rate ranging from 5% to 25% of periorbital or orbital cellulitis with intracranial complications.

Pathophysiology

The most common bacterial causes of periorbital cellulitis are Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes. With increased vaccination, there are fewer cases of Haemophilus influenzae as a causative organism. However, there are now increasing instances of methicillin-resistant Staphylococcus aureus (MRSA) causing periorbital cellulitis. Less common causes are from Acinetobacter, Nocardia, Bacillus, Pseudomonas, Neisseria, Proteus, Pasteurella, and Mycobacterium. While rarer, fungal infections have been documented, specifically from Mucorales and Aspergillus.

The most common inciting events of periorbital cellulitis include sinusitis, hematogenous seeding, direct inoculation of the skin such as with insect bites, periocular or facial trauma, and impetigo. Pathogens causing sinusitis, especially ethmoiditis, spread to nearby tissues through the valveless ophthalmic venous system or the lamina papyracea. In fact, the most common complications of sinusitis are periorbital or orbital involvement and intracranial extension.

Without the proper treatment, periorbital cellulitis can cause orbital cellulitis and loss of vision. In extreme cases, it can extend further to cause a subperiosteal abscess, orbital abscess, cavernous sinus thrombosis, and intracranial infection such as intracerebral abscess, meningitis, empyema or abscess of the epidural or subdural space.

History and Physical

The history and physical exam are essential in the evaluation for periorbital cellulitis. In many cases, there will be a history of sinusitis or upper respiratory infection, trauma, infection from a nearby area, or insect bites. It is important to note ophthalmic complaints, temperature, and swelling. Periorbital and orbital cellulitis present similarly making diagnoses difficult in some scenarios.

Periorbital cellulitis presents with periorbital erythema, edema, and eyelid swelling, Complaints are normally unilateral. Vision, globe motility, and intraocular pressures are usually normal because the infection and inflammation are superficial and anterior to periocular tissue with no involvement of extraocular muscles. In contrast, orbital cellulitis occurs after more extensive infection posterior to the orbital septum. This leads to symptoms such as proptosis, limited extraocular movement, ophthalmoplegia, and decreased vision in addition to eyelid erythema and edema. The absence of fever usually suggests that the infection is preseptal. However, some instances of orbital cellulitis may not have a fever. Also, some cases of periorbital cellulitis have been associated with fever, injected conjunctiva, chemosis, teary eyes, discharge, and some reduction in vision, making it difficult to differentiate from orbital cellulitis.

Furthermore, it is important to differentiate periorbital cellulitis from allergic reactions, trauma without cellulitis, orbital tumors, dysthyroid exophthalmos, chalazion, and hordeolum.

With inadequate treatment, periorbital cellulitis can lead to complications such as orbital cellulitis, subperiosteal abscess, orbital abscess, or cavernous sinus thrombosis, as seen in the Chandler classification of orbital complications. Group 1 of this classification is preseptal cellulitis, inflammation, and edema affecting the soft tissues of the eyelid and other superficial structures. Group 2, orbital cellulitis, is the infection of bacteria within the orbits causing inflammation of the periorbital and orbital adipose tissues causing impaired vision, ophthalmoplegia, pain with eye movement, chemosis, injected conjunctiva, proptosis, fever, and leukocytosis. Group 3, subperiosteal abscess, is the collection of pus between the wall of the orbit and the surrounding periorbital structures causing a displaced globe in the lateral or downward direction. Patients will have limited movement and present with proptosis. This abscess can rupture through the orbital septum and present in the eyelids or rupture posteriorly into the orbital space to form a true orbital abscess, which is group 4. Group 4, orbital abscesses, is a discrete collection of pus that develops within the orbital tissue leading to exophthalmos, chemosis, severe vision impairment, and ophthalmoplegia. This abscess can also extend anteriorly and rupture into the eyelids. Group 5, cavernous sinus thrombosis, results from the further progression into the cavernous sinuses leading to symptoms in the opposite eye. In very severe cases, patients may have meningitis. Although not always a true continuum, the conditions in this classification system present similarly and must be considered during the evaluation of a patient with ophthalmic complaints.

Evaluation

The diagnosis of periorbital cellulitis is mainly a clinical diagnosis with radiologic findings. In many cases, the clinical distinction between periorbital and orbital cellulitis is unclear. A CT scan of the orbits and sinuses allows differentiation of the two conditions, as well as a way to determine the extent of the infection. If it is still unclear, patients are treated as if they have the diagnosis of orbital cellulitis. In cases where abscesses are suspected, a CT head is required to rule out intracranial involvement. A CT scan is also recommended if marked eyelid swelling, fever, leukocytosis, or no improvement after 24 hours of the proper antibiotics.

The CT scan of periorbital cellulitis will show eyelid swelling, no proptosis, no fat stranding of orbital contents, and no involvement of the extraocular muscles. One study found that 41% of patients with periorbital cellulitis had evidence of sinusitis on CT scan.

Blood cultures are not performed routinely. They are difficult to obtain in those with periorbital cellulitis and are almost always negative.

Treatment / Management

The treatment of periorbital cellulitis differs based on the severity of disease and age of the patient. The mainstay of treatment is usually antibiotic coverage against S. aureus, the Streptococcus species, and anaerobes. Patients who are over one year of age with mild symptoms can be treated as an outpatient with oral antibiotics. Those with more severe disease or are less than one year of age, should be admitted to the hospital.

Prior treatment of periorbital cellulitis included amoxicillin-clavulanic acid, cefpodoxime or cefdinir. However, this is no longer recommended due to the rise of MRSA. For MRSA coverage, it is recommended that patients receive Trimethoprim-sulfamethoxazole (TMP-SMX), Clindamycin, or Doxycycline, however, TMP-SMX and doxycycline do not cover group A Streptococcus and doxycycline is not recommended for children under eight years of age. The current recommendation is Clindamycin or TMP-SMX plus Amoxicillin-clavulanic acid or Cefpodoxime or Cefdinir. If the patient is unimmunized by H.influenzae, antibiotic coverage with a beta-lactam is recommended. The antibiotic course is usually for five to seven days or longer if the cellulitis persists.

Response to antibiotics is usually rapid and complete. If outpatient therapy fails to show improvement after 24 to 48 hours, patients should be hospitalized with broad-spectrum antibiotics, CT scan, and a surgical consultation should be considered for possible incision and drainage. No studies have shown an association between steroids and the recurrence or complication of orbital cellulitis, and thus steroids are not routinely prescribed.

For patients with group 3, 4, or 5 of the Chandler classification, surgery is necessary for drainage. Also, if a clinician is unsure if a patient has periorbital or orbital cellulitis even with a CT scan, it is recommended to treat as orbital cellulitis. [9][10](A1)

Differential Diagnosis

• Angioedema 

• Insect bites

• Cavernous sinus thrombosis

• Chalazion

• Internal and external hordeola

• Mucormycosis

• Nephrotic syndrome

• Orbital cellulitis

• Pott's puffy tumour

• Periorbital necrotizing fasicitis