Orbital Cellulitis

Complex
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Diagnosis and reasoning

This young girl has presented with acute left-sided orbital erythema and swelling, a highly concerning constellation of symptoms which mandates urgent evaluation. Examination reveals chemosis and proptosis of the affected eye, along with pain with eye movements; when considered along with the symptoms, and the history suggestive of preceding sinusitis, orbital cellulitis is a strong consideration. Given the rapid onset of symptoms, the other potential differential diagnoses are probably cavernous sinus thrombosis and periorbital cellulitis. However, the latter is not associated with proptosis, or pain on eye movements, while systemic symptoms such as fever are also uncommon. Neither are there superficial skin injuries which would favor preseptal infection. Septic cavernous sinus thrombosis can also occur secondary to sinus infection, and closely emulate the findings of orbital cellulitis; however, this is clinically less likely in the absence of neurological findings such as visual disturbances, lateral gaze palsy, ptosis, mydriasis, or ophthalmoplegia. That said, these two clinical entities can be extremely difficult to differentiate; imaging studies are essential to establish the diagnosis. Contrast computed tomography (CT) of the orbits and brain, in turn, reveals a small left-medial subperiosteal abscess, thus showing the diagnosis to indeed be orbital cellulitis; the left ethmoid sinusitis is the likely underlying source. Note also that there are no features of meningism, or imaging findings suggestive of intracranial extension; thus, there is no clear justification to perform a lumbar puncture here. Empirical broad-spectrum intravenous (IV) antibiotics are the mainstay of therapy and should be commenced as soon as possible. Blood cultures should be obtained beforehand, and the antibiotic regimen adjusted accordingly, once results are available. Nasal decongestants will be of use in improving nasal drainage, thus helping improve the underlying sinusitis. Surgical drainage is not indicated here as the abscess is small, while vision is unaffected, and the intraocular pressure still normal. Furthermore, while inpatient therapy is a must, there is little additional benefit in her being treated in an intensive care setting.


Discussion

Orbital cellulitis is an invasive bacterial infection of the postseptal tissues of the eye; it is an ophthalmological emergency which is sight-threatening, and in the absence of proper treatment, potentially life-threatening as well. The condition is most frequently encountered in children, particularly below the age of 15 years, with almost twice as many cases occurring in males as compared to females. Sinusitis, particularly that of the ethmoid sinuses, is usually the underlying source of infection. In this, there is bacterial spread via the edematous mucosa of the ethmoid sinus, into the wafer-thin medial wall of the orbit (lamina papyracea), resulting in suppuration and subperiosteal abscess formation. As the abscess enlarges, the intraorbital pressure rises, resulting in chemosis, proptosis, and ophthalmoplegia, the classical signs of the condition. Note that the orbital septum (a fibrous extension of the frontal bone periosteum) inserts into the tarsal plate of the upper lid, dividing this area into the preseptal and postseptal compartments; thus, the infection typically remains confined to the postseptal region. The above is also key in differentiating orbital cellulitis from periorbital cellulitis; the latter is typically confined to the superficial tissues (i.e. the preseptal compartment) and is a considerably less severe disease. Key causative organisms include Staphylococcus aureus and Streptococcus spp; Haemophilus influenza was the most common cause before widespread vaccination became common. Less often, anaerobes from the oral cavity are implicated, particularly where the infection has spread from the maxillary sinus. In immunocompromise, fungi such as Mucor spp and Aspergillus spp should also be suspected. Initially, patients may complain of sinusitis followed by painful eye swelling and headache. The presence of fever, disturbances in vision, and pain with eye movements helps differentiate orbital cellulitis from periorbital infection. Examination may reveal conjunctival chemosis, proptosis, and erythema and tenderness of the overlying skin. If the abscess is large, strabismus and ophthalmoplegia may also be present. Contrast computed tomography (CT) of the orbits and brain is the imaging study of choice; this will confirm the inflammation to be postseptal in location, demarcate the size and extent of the subperiosteal abscess, and detect if intracranial extension has occurred. Basic laboratory studies are also of value; a complete blood count (CBC) will typically show marked leukocytosis, corresponding to the extensive bacterial infection. In cases where periorbital cellulitis is initially suspected, this is helpful in raising consideration of orbital cellulitis. Blood cultures should also be obtained prior to antibiotic administration, although these are positive in less than one-third of cases. Where intracranial extension of the infection is suspected (for example, if there are signs of meningism), lumbar puncture may also be considered. Where orbital cellulitis is suspected, empirical broad-spectrum intravenous (IV) antibiotics should be commenced as soon as is possible; vancomycin, ampicillin-sulbactam, and piperacillin-tazobactam are the agents of choice, while antifungal drugs may be added in immunocompromised individuals. IV antibiotic therapy should be continued for at least for seven to ten days, followed by oral therapy for at least another two weeks, so as to ensure complete eradication of the bacteria. Surgical drainage is indicated if the abscess is large, or if the intraorbital pressure is elevated to the point where optic nerve and retinal decompensation has taken place or is in danger of occurring. Note that small subperiosteal abscesses can be treated medically alone, with close follow-up. Nasal decongestants can be used to ensure resolution of the sinusitis. Furthermore, as might be obvious, these patients should initially be treated in an inpatient setting, and ophthalmological and otolaryngological opinions should be obtained. The complications of orbital cellulitis are usually related to extension of the infection, either locally or systemically. The former include corneal disease, uveitis, and exudative retinal detachment leading to vision loss; cavernous sinus thrombosis and intracranial extension may occur in late cases. Overall, early detection and treatment results in a good prognosis; conversely, where left untreated, high rates of morbidity and mortality occur.


Take home messages

  1. Orbital cellulitis is a sight-threatening ophthalmological emergency which mandates early diagnosis and treatment.
  2. Differentiation between periorbital cellulitis and orbital cellulitis is crucial, as the former is a much less severe condition which can be managed using oral antibiotics in an outpatient setting.
  3. Contrast computed tomography (CT) of the orbits is key in confirming the diagnosis and detecting complications.
  4. Intravenous broad-spectrum antibiotics are the mainstay of therapy and should be commenced as soon as possible.

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