Laboratory Studies
Laboratory studies include the following:
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Complete blood count (CBC) with differential
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Blood cultures
- Recent literature shows a yield of 0-2% in patients with orbital cellulitis and may not be indicated in the immunized patient.
- Minimally invasive culture techniques such as nasal swabs or eye discharge cultures yield a higher percentage of positive cultures than do blood cultures.
- Elevated serum glucose level
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Ketoacidosis or electrolyte abnormalities should be rapidly corrected.
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Arterial blood gas (ABG) in debilitated patients or in patients with elevated blood glucose level
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Inflammatory markers such as C-reactive protein (CRP), sedimentation rate, and procalcitonin may aid in differentiating infectious processes from noninfectious ones.
Imaging Studies
Imaging studies include the following:
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Computed tomography (CT) scan - Orbit, sinuses, and frontal lobe
CT scan is an easily available, cost-effective investigational modality that can immediately provide images of the orbit, sinus, and head for every patient showing signs of orbital involvement. Of note, literature shows that the radiation exposure of routine CT scans may increase the prevalence of cancer-induced mortality over a lifetime to 0.1%. New recommendations are to keep the radiation doses as low as possible, especially in the pediatric patient. [19]
If a brain abscess is suspected or if the patient has HIV, consider a head CT scan to exclude mass lesions before performing a lumbar puncture (LP).
Contrast generally is required because of the surrounding bony structures of the orbital apex artifacts that may be encountered.
Consider CT venography to evaluate the possibility of CST and the overall contiguity of the cavernous sinus.
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MRI: Although CT scanning is the predominant initial investigation of choice, MRI is superior in evaluating the soft tissues of the orbit because the resolution allows for better differentiation of diseased from normal tissue; specifically, it allows one to identify intracranial dissemination of infection or cerebral infarction.
MRI improves visualization of cavernous sinus. [20]
Contrast-enhanced orbital MRI (specifically gadolinium-based intravenous contrast) has been used in to assess the extent of ophthalmological disease when there is a high index of suspicion for visual compromise secondary to disseminated infection. [21]
Magnetic resonance venography (MRV) can be used to noninvasively evaluate flow in the cavernous sinus and shows a filling effect in patients with CST.
MRI diffusion-weighted imaging (DWI) is a technique that uses discrepancies in the diffusion properties of tissue water molecules to discriminate orbital infections from hematomas, tumors, or ischemia/infarction. In a retrospective study by Sepahdari et al, DWI improved diagnostic confidence when other contrast-enhanced images (ie, T1-weighted contrast-enhanced images with fat-suppression) are equivocal. DWI has been suggested to be helpful in providing confirmation of intracranial extension of orbital abscesses and in the diagnosis of CST. [22]
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Ultrasonography of the orbit can miss posterior abscesses and is best used for evaluation of the globe itself (lens, vitreous, retina, and optic disc). As stated earlier, this modality may be used more frequently in evaluating the presence or absence of papilledema.
Other Tests
Other tests may include the following:
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Fiberoptic nasopharyngeal endoscopy: If any suspicion of mucormycosis (ie, elevated blood glucose, leukemia, renal disease, deferoxamine therapy) exists, fiberoptic nasopharyngeal endoscopy should be performed (usually, by an otolaryngologist) to seek evidence of black eschar formation.
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Slit-lamp examination to rule out endophthalmitis and other noninfectious causes of proptosis
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Rapid plasma reagin (RPR), particularly in cases of insidious onset or with a history of syphilis
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In clinical examinations suggestive of meningitis, cerebrospinal fluid (CSF) analysis for Gram stain and culture, cell count, CSF glucose and protein, and viral and fungal antigen testing
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Complications of orbital infections. Brain abscess in a young man secondary to an orbital infection from Mucor species.
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Orbital infections. Orbital abscess with significant proptosis.
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Orbital infections. Subperiosteal abscess with contiguous sinusitis.
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Orbital infections. Subperiosteal abscess with contiguous sinusitis.
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Orbital infections. Frontal sinusitis.
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Orbital infections. Orbital abscess with significant proptosis.
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Cavernous sinus and its cranial nerves.
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Orbital cellulitis; chemosis.
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Lamina papyracea.
