There are several sight-threatening ocular conditions that are true medical emergencies that optometrists must be ready to manage at any given time, with orbital cellulitis being one such condition. Optometrists can encounter cellulitis in two forms—periorbital and orbital.
Fortunately, diagnosing and distinguishing between these two conditions is straightforward, especially with an understanding of the orbital architecture. This article will provide a quick and concise walkthrough of periorbital and orbital cellulitis, along with an essential diagnostic checklist available for download.
Distinguishing periorbital and orbital cellulitis
Distinguishing between periorbital and orbital cellulitis is crucial due to the significant difference in potential complications. Periorbital cellulitis is typically a superficial infection, while orbital cellulitis is a deeper infection that requires more aggressive treatment.
Early and accurate diagnosis is essential for ensuring appropriate management and preventing vision- and even life-threatening outcomes.
The role of the orbital septum
The basis of differentiating between periorbital and orbital cellulitis lies in the orbital architecture, specifically the orbital septum. The orbital septum is a membranous tissue that divides the orbit, separating the preseptal orbicularis muscle and eyelid skin from the deeper postseptal contents, which include the orbit, orbital fat, and extraocular muscles.1
Although the orbital septum serves as a barrier, infections can spread from the preseptal to the postseptal regions through the facial and ophthalmic venous systems, allowing periorbital cellulitis to progress to orbital cellulitis.1
Figure 1: Anatomical diagram highlighting the difference between periorbital (preseptal) and orbital cellulitis.
Periorbital cellulitis: An overview
Periorbital cellulitis, also known as preseptal cellulitis, is an infection of the periocular skin and soft tissues located anterior to the orbital septum.1
A patient with periorbital cellulitis may have a recent history of sinusitis, an upper respiratory tract infection, trauma, such as an eyelid laceration, an adjacent infection like a recent hordeolum,2 or an insect bite.1
Signs and symptoms of periorbital cellulitis
Unilateral periorbital edema, swelling, tenderness, and eyelid redness are characteristic signs of acute periorbital cellulitis. Some patients with periorbital cellulitis may also have conjunctival injection and watery eyes, resulting in only a slight reduction in vision.
Although patients with periorbital cellulitis can have a low-grade fever, this is most commonly associated with orbital cellulitis and should be treated as such until proven otherwise. Extraocular motility, pupillary function, and visual acuity are unaffected because infection and inflammation are confined to the preseptal space.1
Risk factors for periorbital cellulitis include:
- Age: Being under the age of 16 is the greatest risk factor, as periorbital cellulitis is more common in the pediatric population.1,3 Although less common, periorbital cellulitis tends to present with more severe cases in adult patients.3
- Gender: Although some studies suggest a slightly greater prevalence in male patients, periorbital cellulitis appears to affect males and females equally.3
- Comorbidities: Patients with chronic sinusitis, diabetes, human immunodeficiency virus (HIV), leukemia, or weakened immune systems are at greater risk of developing periorbital cellulitis.4
Figure 1: Slit lamp image of a patient with periorbital cellulitis.
Figure 1: Preseptal cellulitis© Afrodriguezg. Image used under CC BY-SA 3.0.
Download the Periorbital and Orbital Cellulitis Differential Diagnosis Cheat Sheet here!
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Periorbital and Orbital Cellulitis Differential Diagnosis Cheat Sheet
Use this cheat sheet to differentiate between periorbital and orbital cellulitis, with information on exam findings, risk factors, and tips for diagnosing and managing each.
Differential diagnoses for periorbital cellulitis
The diagnosis of periorbital cellulitis is based on clinical evaluation and radiological findings.1 Many conditions resemble periorbital cellulitis and can be categorized based on their etiology, including allergic reactions, systemic illnesses, and infectious processes.
Allergic reactions
Angioedema is an allergic reaction that causes swift, painless, non-tender swelling in the deeper layers of the skin. It is frequently associated with systemic allergic reactions and responds to antihistamines, corticosteroids, or epinephrine.5
Orbital lesions
Orbital tumors, such as lymphomas or schwannomas, are benign or malignant growths in the orbital region. They differ from periorbital cellulitis due to their gradual onset, lack of infection, and the presence of a palpable mass.6
Systemic conditions
Several systemic conditions can lead to a mistaken diagnosis, including:
- Thyroid eye disease: Can cause proptosis of the globe, presenting gradually without redness or swelling of the eyelids and without infection.7
- Nephrotic syndrome: A systemic condition that causes generalized edema, including periorbital swelling due to protein loss in urine.
- Nephrotic syndrome is distinguished from periorbital cellulitis by its diffuse, bilateral presentation with the absence of infection, pain, or tenderness.8
- Insect bites: Can cause localized swelling and inflammation in the periorbital region but typically do not involve infection or pus formation, unless in unusual cases of spider bites.1
- Traumatic injuries: These injuries to the periorbital area can cause swelling and bruising without infection.1
Infections
A number of infections resemble periorbital cellulitis, among them are:
- Hordeola and chalazia: Can appear similar to periorbital cellulitis, with eyelid swelling and redness. Further, hordeola or chalazia can develop into periorbital cellulitis through the spread of infection or inflammation to the surrounding tissues.1
- Mucormycosis: In contrast to periorbital cellulitis, is a fungal infection of the sinuses that progresses quickly, results in tissue necrosis, and affects deeper orbital tissues.9
- Periorbital necrotizing fasciitis: A severe bacterial infection that is distinguished by widespread tissue involvement, accelerated tissue death, intense pain, and systemic inflammation.10
- Pott’s puffy tumor: A complication of frontal sinusitis causing swelling in the forehead and surrounding areas. This tumor can be recognized by the presence of fever, more prominent forehead swelling, and bone involvement.11
- Cavernous sinus thrombosis: Can be caused by infection of adjacent structures that lead to a blood clot in the cavernous sinus. It is identified by the presence of severe headaches, extraocular motility restrictions, and signs of cranial nerve involvement.12
- Orbital cellulitis: The most crucial condition that should be ruled out during the differential diagnosis of periorbital cellulitis and will be discussed in detail in the upcoming section.
Assessment using CT and cultures
Computed tomography (CT) scans of the orbits and sinuses can assess the extent of the infection and differentiate periorbital cellulitis from orbital cellulitis. CT scans in patients with periorbital cellulitis typically show eyelid swelling without proptosis or involvement of the extraocular muscles.1
Cultures of eyelid wounds, conjunctival discharge, or nasal fluid should be collected to determine the appropriate antibiotic based on bacterial sensitivity.1,2
Management/treatment of periorbital cellulitis
Treatment of periorbital cellulitis varies depending on the severity of the infection and the patient's age.
Oral antibiotics
Empiric oral antibiotic therapy should target Staphylococcus aureus, Streptococcus species, and anaerobes. Due to the rise of methicillin-resistant S. aureus (MRSA), the current recommendation is clindamycin or trimethoprim-sulfamethoxazole (TMP-SMX) in combination with amoxicillin-clavulanic acid, cefpodoxime, or cefdinir for 5 to 7 days.1
It is important to take any allergies into account when prescribing oral antibiotics for patients with periorbital cellulitis, such as allergies to penicillin or sulfa.
Intravenous antibiotics
Patients with periorbital cellulitis should be closely monitored to ensure that the infection does not progress to orbital cellulitis. The response to oral antibiotics should be swift.
If there is no improvement after 24 to 48 hours, intravenous antibiotic therapy with hospitalization should be initiated immediately.1
Orbital cellulitis: An overview
Orbital cellulitis is a serious bacterial infection that affects the structures located posterior or behind the orbital septum, which include the extraocular muscles, orbital fat, and nerve and blood supply within the bony orbit.13
Progression of orbital cellulitis can cause meningitis, an inflammation of the brain and spinal cord membranes, and the formation of pus accumulation, or abscesses.
Severe and irreversible loss of vision occurs with inflammation from intracranial and orbital abscesses creating:13
- Mechanical compression of the optic nerve, leading to optic neuropathy
- Ischemia and occlusion of the orbital vasculature resulting in central retinal artery occlusions
An advancing infection can result in cavernous sinus thrombosis, a blood clot within the cavernous sinus in the brain. Although rare, cavernous sinus thrombosis is life-threatening and illustrates the most harmful consequence of orbital cellulitis.13
Signs and symptoms of orbital cellulitis
Consequently, accurate diagnosis and timely treatment of orbital cellulitis are critical for preventing complications resulting in vision loss and fatal outcomes. Acute orbital cellulitis presents with most of the same signs and symptoms as periorbital cellulitis, including unilateral periorbital edema, swelling, tenderness, and eyelid redness.
Also, conjunctival injection and chemosis, along with a low-grade fever, are common in patients with orbital cellulitis.13,14 Although a fever is common in orbital cellulitis, it may not be present in all cases. However, the presence of a low-grade fever or any of the following diagnostic signs should serve as a warning that the condition has orbital involvement.
Infection and inflammation of the specific structures in the postseptal space leads to impaired function, thereby creating the classic distinguishing signs of orbital cellulitis.
The diagnostic hallmarks of orbital cellulitis are:13,14
- Afferent pupillary defect
- Decreased visual acuity
- Diplopia
- Limited ocular motility
- Pain with eye movements
- Proptosis
Figure 2: Slit lamp image of a pediatric patient with orbital cellulitis.
Figure 2: Child with left orbital cellulitis© Dayakar Yadalla, Rajagopalan Jayagayathri, Karthikeyan Padmanaban, et al. Image used under CC BY-NC-SA 4.0.
Don't forget to check out the differential diagnosis cheat sheet!
Risk factors for orbital cellulitis
There are a multitude of risk factors to consider that lend themselves to an increased risk of orbital cellulitis.
Risk factors for orbital cellulitis to consider:
- Bacterial sinusitis: The most common predisposing risk factor across all age groups in patients with orbital cellulitis.13,14
- Upper respiratory tract infections: Another major risk factor for orbital cellulitis as upper respiratory tract infections can spread to the orbit.13,14
- Dental infections: Can spread to the orbit via the infraorbital sinuses, resulting in orbital cellulitis.13,14
- Ear infections: Especially of the middle ear, can increase the risk of developing orbital cellulitis.14
- Immunodeficiency: Makes patients more susceptible to orbital cellulitis due to a reduced ability to fight infections caused by pathogens.13,14
- Ocular conditions:
- Orbital trauma, such as a blow-out fracture or penetrating foreign body, increases the risk for developing orbital cellulitis due to disruption of the orbital structures and the introduction of bacteria into the postseptal space.13
- Recent ophthalmic surgery, such as blepharoplasty or other procedures requiring peribulbar anesthesia, also increases the risk of developing orbital cellulitis.13,14
- Orbital cellulitis is more likely to occur in patients with ocular infections, such as dacryocystitis.14
Testing/diagnosis of orbital cellulitis
The diagnosis of orbital cellulitis relies on a combination of clinical findings, laboratory tests, and imaging studies.13
Clinical exam
Diagnostic testing and patient examination should focus on identifying or ruling out the characteristic signs of orbital cellulitis. A thorough exam must include assessment of constitutional symptoms (i.e., fever), pupillary function, extraocular motility, visual acuity, and proptosis.14
Laboratory tests
Prior to prescribing antibiotics, blood cultures for common bacterial pathogens, and fungi and mycobacteria if indicated, should be collected from patients with suspected orbital cellulitis.14
Imaging to detect orbital cellulitis
Imaging tests that optometrists can use to identify orbital cellulitis include:
- CT imaging: The most commonly used radiologic technique due to the widespread availability of CT scanners. Common CT findings in orbital cellulitis include:13,14
- Inflammation of the extraocular muscles
- Anterior displacement of the globe
- Fat stranding, which refers to streaky or web-like areas in the orbital fat that appear denser, indicating inflammation or edema within the fat
- Magnetic resonance imaging (MRI): Effective when CT results are inconclusive, as MRI is more sensitive in imaging soft tissue.13
Criteria for differential diagnosis of orbital cellulitis
Various conditions have the appearance of orbital cellulitis, having similar features such as proptosis, chemosis, and periorbital swelling.
Ocular conditions with the absence of fever
Several ocular disorders, such as adenoviral conjunctivitis, orbital pseudotumor, posterior scleritis, retinoblastoma, and retrobulbar hemorrhage, can produce proptosis, eyelid swelling, or pain with eye movement but are distinguished from orbital cellulitis by the absence of fever.
Ocular conditions to consider that present without fever:
- Adenoviral conjunctivitis: Typically does not cause diplopia or pain with eye movements.15
- Posterior scleritis: Scleral thickening or inflammation in posterior scleritis can be detected by MRI or ultrasound tests.16
- Orbital pseudotumor: Will demonstrate soft tissue inflammation without abscess formation on CT or MRI scans.17
- Retinoblastoma: Strabismus and leukocoria are seen in cases of retinoblastoma with posterior segment masses found during ultrasound or MRI scans.18
- Retrobulbar hemorrhage: Usually occurs after trauma or an orbital fracture. CT or MRI scans will show blood in the retrobulbar space.19
Systemic diseases
Systemic diseases can display inflammatory features, causing proptosis similar to orbital cellulitis, but can be differentiated by their chronic progression without infectious signs like fever or discharge.
Rheumatologic conditions
Rheumatologic conditions such as granulomatosis with polyangiitis, polyarteritis nodosa, giant cell arteritis, and sarcoidosis, a systemic granulomatous disease, can be excluded by their lack of infectious signs.13
Sickle cell and thyroid ophthalmopathy
Differential diagnosis of other systemic conditions such as sickle cell orbitopathy and thyroid ophthalmopathy can be made through imaging; sickle cell orbitopathy reveals bone marrow infarcts and hematomas,20 while thyroid ophthalmopathy typically shows muscle enlargement without fat stranding.7
Neoplastic disorders
Neoplastic disorders may appear like orbital cellulitis but differ by gradual onset, lack of fever, and absence of significant inflammatory signs such as pain with eye movements or eyelid redness.
These cancers include:
- Primary neoplasms
- Rhabdomyosarcoma
- Retinoblastoma
- Malignant melanoma
- Acute diseases
- Leukemia
- Ocular adnexal T-cell lymphoma
- Extranodal natural killer (NK)/T-cell lymphoma6
- Neoplasms that have spread to the orbit13
- Esophageal adenocarcinoma
- Urothelial carcinoma
- Neuroblastoma
- Rectal adenocarcinoma
- Lung carcinoma
Insect bites
Widow spider envenomation refers to the poisoning caused by the bite of a widow spider. Pain, swelling, and redness can occur if bitten near the eyelid or orbital area.
In contrast, widow spider envenomation is usually associated with systemic symptoms such as muscle pain, abdominal cramping, and sweating. Diagnosis is based on a history of a spider bite and absence of fever.21
Pediatric presentations of orbital cellulitis
Langerhans cell histiocytosis (LCH)
Langerhans cell histiocytosis is a rare neoplastic disorder primarily affecting children. Symptoms include bone lesions, lymphadenopathy, proptosis, periorbital swelling, and eye movement pain. Fever may or may not be present. Diagnosis is made through biopsy and immunohistochemistry.22
Pediatric mucormycosis
Pediatric mucormycosis, a serious and rare fungal disease that affects children with weakened immune systems. There is sinus involvement extending to the orbit with proptosis, eyelid swelling, and pain with eye movements.
However, there is a rapid onset of black eschar, a hardened, black tissue formed from tissue necrosis. Fever can occur in later or more severe cases. Cultures and imaging tests can differentiate orbital cellulitis from mucormycosis.23
Trauma with absence of fever
Carotid cavernous fistula, a high-pressure vascular connection between the carotid artery and cavernous sinus, often presents with pulsatile exophthalmos and audible bruit.24 Cranio-orbital cerebrospinal fluid leaks are characterized by clear, watery discharge. Both conditions can be confirmed by MRI or CT.25
Management/treatment of orbital cellulitis
Management of orbital cellulitis concentrates on aggressive intravenous antibiotic therapy with concurrent treatment of any underlying predisposing factors, such as bacterial sinusitis.
Empiric IV antibiotic regimens lasting 2 to 4 weeks for patients with normal renal function include vancomycin and metronidazole, combined with one of the following: ceftriaxone, cefotaxime, ampicillin-sulbactam, or piperacillin-tazobactam.
Surgical intervention is sometimes necessary if there is sinus involvement that needs surgical correction, a foreign body needs removed, or to obtain cultures. Surgery, such as drainage of orbital abscesses, is also indicated in patients with intracranial progression of the infection.13,14
Key takeaways
Periorbital cellulitis, primarily affecting superficial tissues, presents with eyelid swelling and redness without visual or motility deficits. In contrast, orbital cellulitis involves deeper structures, distinguished by diplopia, pain with eye movement, proptosis, and changes in vision or pupillary response often accompanied by a fever.
Recognizing the risk factors and differential diagnosis criteria of periorbital and orbital cellulitis is essential for ensuring timely and accurate diagnosis to guide treatment and prevent vision- and life-threatening complications.
