Orbital Infection Imaging_ Overview, Computed Tomography, Magnetic Resonance Imaging

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Orbital Infection Imaging

Author: Claudia F E Kirsch, MD Chief Editor: James G Smirniotopoulos, MD more...

Updated: Oct 07, 2015

Overview

hen discussing orbital infections, understanding the clinical differences between

an ocular versus an orbital infection is important. [1, 2] The orbit includes the bone,periorbita, ocular muscles, retroseptal fat, and optic nerve and is consideredseparately from the globe. The globe is contained by the sclera and lies within the

fascial envelopeof the Tenon capsule. Orbital cellulitis, an orbital infection resultingfrom a sinus infection, is seen in the image below.

Axial computed tomography scan of orbital and facial cellulitis.

An ocular infection is defined as being limited to the globe or intraocular tissue.

Ocular disease, such as infectious scleritis, endophthalmitis, cytomegalovirus (CMV)retinitis, and syphilitic chorioretinitis, is typically diagnosed using direct

ophthalmologic examination. Radiographic evaluation using computed tomography(CT) scanning and magnetic resonance imaging (MRI) has limited usefulness in theassessment of these disease entities, although dedicated ophthalmic

ultrasonography may be a useful adjuvant.[3]

CT scanning and MRI may be helpful in distinguishing an endophthalmitis withlimited secondary extraocular inflammation from a true panophthalmitis withinfected orbital tissue. In addition, diffusion-weighted imaging (DWI) in MRI shows

utility in assessing the optic nerves for developing ischemia or infarction, which may

occur during orbital infections.[4, 5]

Classification of orbital infections

Although the orbital complications of sinus infections are usually classified as orbital

cellulitis, treatment of this disease requires a more complete description. [6] Chandler

et al defined the following categories of orbital infections (images of which are

presented below)[7] :

Inflammation with edemaOrbital cellulitis

Subperiosteal abscess (SPA)Orbital abscess

Cavernous sinus thrombosis

Coronal computed tomography scan in a pediatric patient with sinusitis as well as anorbital and subperiosteal abscess.
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Axial computed tomography scan in a patient with an infection caused by Streptococcuspneumoniae and a superior orbital subperiosteal abscess that resulted in blindness.

Coronal computed tomography scan in a pediatric patient with sinusitis and orbitalabscess.

One of the most important clinical and radiographic questions regarding these

categories is whether the orbital infection is preseptal or postseptal.

See below for a series of CT scans and MRIs from a case.

Axial postcontrast CT sc an of a 56-year-old woman with concern for orbital infection. Note theleft orbital proptosis there are both preseptal and postseptal inflammatory changes, withstranding of the left intraconal fat planes. In this patient, the diagnosis was mucormycosis andwas highly worrisome for angioinvasive spread to the cavernous sinus, which can lead tocavernous s inus thrombosis.
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Same patient as in the axial image (56-year-old woman with concern for mucormycosis)corresponding postcontrast coronal CT scan with findings worrisome for cavernous sinusthrombosis.

MRI (1.5 Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 2 days after a left orbital exenteration. Abnormal enhancement can be noted along thecourse of the cisternal segment of the left trigeminal nerve, associated with restricted diffusion,with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons.Redemonstration of a left cavernous sinus thrombosis can be seen. The findings are worrisomefor continued angioinvasive spread of the mucormycosis into the left lateral pons.

MRI (1.5 Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 2 days after a left orbital exenteration. Abnormal enhancement can be seen along thecourse of the cisternal segment of the left trigeminal nerve, associated with restricted diffusion,with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons.Redemonstration of a left cavernous sinus thrombosis can be seen. The findings are worrisomefor continued angioinvasive spread of the mucormycosis into the left lateral pons.


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MRI (1.5 Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 2 days after a left orbital exenteration. Abnormal enhancement can be seen along thecourse of the cisternal segment of the left trigeminal nerve, associated with restricted diffusion,with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons.Redemonstration of a left cavernous sinus thrombosis can be seen. The findings are worrisomefor continued angioinvasive spread of the mucormycosis into the left lateral pons.

MRI (1.5 Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 1 week after the prior MRI continued abnormal enhancement is seen along the courseof the cisternal segment of the left trigeminal nerve, with progression of the associated restricteddiffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateralpons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci ofrestricted diffusion are now noted along the left medial temporal lobe, which are worrisome forcontinued progression of disease and the development of new areas of ischemic change.

MRI (1.5 Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 1 week after the prior MRI continued abnormal enhancement is seen along the courseof the cisternal segment of the left trigeminal nerve, with progression of the associated restricteddiffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateralpons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci ofrestricted diffusion are now noted along the left medial temporal lobe, which are worrisome forcontinued progression of disease and the development of new areas of ischemic change.


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MRI (1.5-Tesla) of the same patient (56-year-old woman with concern for orbital infection)obtained 1 week after the prior MRI continued abnormal enhancement is seen along the courseof the cisternal segment of the left trigeminal nerve, with progression of the associated restricteddiffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateralpons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci ofrestricted diffusion are now noted along the left medial temporal lobe, which are worrisome forcontinued progression of disease and the development of new areas of ischemic change.

Recent studies

Sepahdari et al reported on the role of DWI in detecting orbital abscess as a

complication of orbital cellulitis. The authors also assessed whether abscess can bediagnosed with a combination of conventional unenhanced sequences and whole-

brain DWI with parallel acquisition.

In the study, DWI improved diagnostic confidence in nearly all cases of orbitalabscess when used in conjunction with contrast-enhanced imaging. In addition, DWI

confirmed abscess in a majority of cases, without contrast-enhanced imaging(indicating that DWI alone can be diagnostically effective when the use of contrast

material is contraindicated).[8]

Kapur et al identified the role of DWI in differentiating orbital inflammatory

syndrome, orbital lymphoid lesions, and orbital cellulitis. The authors found asignificant difference between these conditions in DWI intensities, apparent

diffusion coefficients (ADCs), and ADC ratios.

In the study, Kapur et al noted that lymphoid lesions were significantly brighter thanorbital inflammatory syndrome and that orbital inflammatory syndrome lesions were

significantly brighter than cellulitis. In addition, lymphoid lesions showed lower ADChan orbital inflammatory syndrome and cellulitis, and a trend was seen toward

lower ADC in orbital inflammatory syndrome than in cellulitis.[9]

Preferred examination

CT scanning is often the first imaging modality that is used because of its ease and

availability at most medical institutions.[10, 11, 12]

On CT scans, a preseptal cellulitis may appear as an area of increased density, with

swelling of the anterior orbital tissues and obliteration of the adjacent fat planes.hen the infection progresses, an increase in the density of the orbital fat may

occur with gradual development of more discrete densities that, in turn, may

progress to formation of an orbital abscess.

If the infection is secondary to an underlying sinusitis, this may manifest as an

SPA. CT scanning is also usually the first imaging modality of choice to identify anSPA, which may be located just lateral to the lamina papyracea.

In pediatric patients, ophthalmic ultrasonography, in skilled hands, may be a usefuladjuvant for the rapid evaluation of preseptal versus postseptal involvement, as wellas a useful modality for a follow-up examination. However, ultrasonography is

limited in its ability to assess intracranial extension, the orbital apex, and paranasal

sinuses.[3]

MRI, especially postgadolinium-enhanced, fat-suppressed sequences, is useful forhe detection of early inflammatory changes within the orbit. On MRI, an orbital

cellulitis appears hypointense on T1-weighted sequences and hyperintense on T2-

weighted sequences. (See the images below.)[13]
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Coronal T1-weighted, postgadolinium, fat-saturated magnetic resonance image in a patient withallergic fungal sinusitis, with extension into the orbit.

Coronal T2-weighted magnetic resonance image of a patient with allergic fungal sinusitis andextension into the orbit.

MRI is also useful for assessing intracranial extension of the infection into thecavernous sinus and for evaluating cavernous sinus thrombosis. DWI in MRI canhelp in the assessment of the optic nerves for developing ischemia or infarction,

which can occur secondarily from orbital infections. [4, 5]

MRI may be useful for evaluating immunocompromised patients who have viralinfections. Because herpes zoster ophthalmicus (HZO) and cytomegalovirus (CMV)may lead to acute retinal necrosis (ARN) and retrobulbar optic neuritis (RBON), MRI

is more sensitive for evaluating pathophysiology in the soft tissues of the opticnerves and radiations, and this modality may demonstrate T2-weighted

hyperintensity and contrast enhancement that extends along the optic nerves, optic

racts, lateral geniculate bodies, optic radiations, and optic cortex.[10]

Plain films have limited usefulness in the diagnosis of orbital infections, especiallywith the advent of CT scanning.

Adjacent tissue may be i nvolved eit her primarily or secondarily in orbital i nfections,such as the lacrimal gland, resulting in dacryoadenitis (seen in the images below),or the lacrimal duct or sac, resulting in dacryocystitis.

Coronal computed tomography scan of a patient who was on steroids and had multiplemyeloma. In addition, the patient had infectious dacryoadenitis with Staphylococcus aureusinfection and an abscess collection.
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Coronal computed tomography scan of a patient with dacryoadenitis and Staphylococcus aureusinfection, resulting in an abscess.

A diagnosis of dacryocystitis is m ade clinically unless adjacent periorbital cellulitis i spresent, limiting the ophthalmologic evaluation. Because the lacrimal sac is a

preseptal structure, radiographic imaging in patients with periorbital cellulitis is ahelpful adjuvant. If only the lacrimal gland is infected and inflamed, the treatment isnonsurgical because of the preseptal location. However, extension into the

postseptal space with a resultant abscess may require surgical treatment. [14, 15]

CT scanning also allows for careful evaluation of the lacrimal sac and nasolacrimalducts to exclude the possibility of a dacryolith, which, although rare, can lead toobstruction of the nasolacrimal ducts and to a resultant dacryocystitis and orbital

infection.

Limitations of techniques

Limitations of MRI include the length of time that is needed to obtain the imagesand the issue of motion artifacts, which may be critical factors in patients who are

extremely ill with cerebral involvement. Metallic foreign bodies and the inability toperform MRI in patients with pacemakers, nonapproved aneurysm clips, or other

devices that are not approved for placement in the MRI scanner are additionallimitations.

Although CT scanning is useful, repeated scans can be damaging t o t he lens. Thus,

imaging studies should be tailored appropriately.

For excellent patient education resources, visit eMedicineHealth's Eye and Vision

Center. Also, see eMedicineHealth's patient education articles Eyelid Inflammation(Blepharitis), Sty, and Foreign Body, Eye.

Computed Tomography

CT scanning is an extremely useful imaging modality in the setting of orbital

infections, especially in detecting SPAs. Orbital cellulitis is usually well visualizedbecause of the low density of fat on the images. Orbital cellulitis and SPAs are

seen in the images below.

Axial computed tomography scan of orbital and facial c ellulitis.

Axial computed tomography scan of orbital and facial c ellulitis.
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Coronal computed tomography scan in a pediatric patient with sinusitis as well as an orbital andsubperiosteal abscess.

Axial computed tomography scan in a patient with an infection caused by Streptococcuspneumoniae and a superior orbital subperiosteal abscess that resulted in blindness.

Axial computed tomography scan in a patient with an infection caused by Streptococcuspneumoniae and a superior orbital subperiosteal abscess.

On CT scans, preseptal cellulitis may appear as an area of increased density withinhe low-density orbital fat. This may represent the first sign of infection, in which

here is obliteration of the normal fat planes and swelling of the anterior orbital softissues.

As the cellulitis progresses, more discrete densities within the orbital f at mayappear. Cellulitis is usually confined to the extraconal space however, if the

infection is allowed to progress, it can enter the muscle cone, resulting in anintraconal infection and abscess formation.

Sinus disease from the ethmoid sinuses may extend into the orbit as an SPA,

which is seen on CT examination as a thin layer of high density immediately lateral

o the lamina papyracea.[16]

Degree of confidence

Although CT scanning is an excellent imaging modality for identifying preseptalcellulitis, SPAs, defects within the lamina papyracea, and dehiscence of the bonymargins of the ethmoid sinus, this technique is not as efficacious in evaluating the

orbital apex because of the surrounding bony structures that may create artifacts in

he region.[16, 11]

False positives/negatives

Hematoma in the subperiosteal space (seen in the image below) can mimic theappearance of a subperiosteal abscess.


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Coronal computed tomography scan in a patient with sickle cell disease. In this image, thepatient has a subperiosteal bleed that mimics the appearance of an infectious subperiostealabscess.

Magnetic Resonance Imaging

MRI is commonly used to assess orbital and soft-tissue disease

[17]

and hasadvantages over CT scanning in this region because of the osseous nature of the

orbital apex and its lack of signal intensity. In addition, MRI may be advantageousin evaluating any infectious process that extends from the orbital apex to the

cavernous sinus. The superior ophthalmic vein and cavernous sinus may beassessed noninvasively by evaluating the vascular flow via gradient-echo imaging.[13]

On MRI, an orbital cellulitis appears hypointense on T1-weighted images andhyperintense on T2-weighted images.

Although T1-weighted images demonstrate the normal f indings of high signalintensity of orbital fat with dark inflammatory changes, and although T2-weightedimages demonstrate the normal findings of dark orbital fat with increased high

signal-intensity inflammatory changes, the most sensitive technique for evaluating

an orbital infection may be postgadolinium, fat-suppressed imaging. [18]

MRI is especially useful in patients who have an aggressive fungal sinusitis, such asmucormycosis and aspergillosis, which has a propensity for extension into the orbit,

cavernous sinus, and neurovascular structures. (Fungal sinusitis is exhibited in theMRI scans below.) Mucormycosis is markedly angioinvasive the fungus grows into

he internal elastic membrane of the blood vessels. The fungal hyphae may thenextend into and occlude the lumina of the blood vessels they have invaded.

Coronal T1-weighted, postgadolinium, fat-saturated magnetic resonance image in a patient withallergic fungal sinusitis, with extension into the orbit.
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Coronal T2-weighted magnetic resonance image of a patient with allergic fungal sinusitis andextension into the orbit.

Axial T1-weighted, postgadolinium magnetic resonance image in a patient with si no-orbital andcavernous sinus mucormycosis.

DWI in MRI has shown utility in assessing the optic nerves for a developing

ischemia or infarction, which may occur during orbital infections. [4, 5]

Gadolinium-based contrast agents have been linked to the development ofnephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD).

NSF/NFD has occurred in patients with moderate to end-stage renal disease afterbeing given a gadolinium-based contrast agent to enhance MRI or MRA scans.NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red

or dark patches on the skin burning, itching, swelling, hardening, and tightening ofhe skin yellow spots on the whites of the eyes joint stiffness with trouble moving

or straightening the arms, hands, legs, or feet pain deep in the hip bones or ribsand muscle weakness.

Ultrasonography

Ultrasonography is usually performed in ophthalmology practices by trained

echnicians using a high-frequency 10-MHz probe. The probe is applied over aclosed eyelid, with the glove in a neutral position and with gentle eye motions from

left to right.

To assess the posterior aspect of the globe, the gain settings are adjusted todampen near-field echoes. To assess the vitreous and central portion of the globe,

he near-field gain is increased.

The center of the lens is anechoic, whereas the midportions of the anterior and the

posterior parts of the lens reflect the ultrasonographic beam, with the iris seen as anechogenic line on either side.

The vitreous humor is anechoic, and the posterior echogenic limit of the globe is the

retina.

Posterior to the globe, the retrobulbar fat is echogenic, with the optic nerve seen as

a hypoechoic structure that extends dorsally away from the posterior margin of the

globe. [19]

Degree of confidence

Ultrasonography requires a dedicated ophthalmologic technician and may not allow

important visualizations of the cavernous sinus and the intracranial extension ofinfections.
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Nuclear Imaging

Nuclear medicine images that use technetium-99m (99mTc) labeled leukocyteshave been useful in the diagnosis of orbital implant infections in patients in whom

CT scans failed to reveal radiographic abnormalities.[20]

Contributor Information and Disclosures

Author

Claudia F E Kirsch, MD Associate Professor of Neuroradiology and Otolaryngology, Department of Radiology,Section Chief for Head and Neck Imaging, Director, Radiology Medical Student Teaching, Wexner Medical

Center, The Ohio State University College of Medicine

Claudia F E Kirsch, MD is a member of the following medical societies: American A ssociation for WomenRadiologists,American College of Radiology,American Roentgen Ray S ociety,American S ociety of FunctionalNeuroradiology,American Society of Head and Neck Radiology,American S ociety of Neuroradiology,Association

of Educators in Imaging and Radiologic Sciences,Association of University Radiologists, British Society of Headand Neck Imaging, Eastern Neuroradiological Society, European Society of Head and Neck Radiology, New York

Academy of Sciences, Radiological Society of North America, Royal College of Radiologists, WesternNeuroradiological S ociety

Disclosure: Received consulting fee from Primal Pictures , for consulting Received grant/research funds fromAdenoid Cystic Carcinoma Research Foundation for other.

Coauthor(s)Roger Turbin, MDConsulting Staff, Department of Ophthalmology, Rutgers New Jersey Medical School

Disclosure: Nothing to disclose.

Devang Gor, MDStaff Physician, Department of Radiology, University of Medicine and Dentistry of New Jersey


Specialty Editor Board

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, HuttValley District Health Board, New Zealand


C Douglas Phillips, MD, FACR Director of Head and Neck Imaging, Division of Neuroradiology, New York-Presbyterian Hospital Professor of Radiology, Weill Cornell Medical College

C Douglas Phillips, MD, FACR is a member of the following medical societies: American College of Radiology,American Medical A ssociation,American Society of Head and Neck Radiology,American S ociety of

Neuroradiology,Association of University Radiologists, Radiological Society of North America


Chief EditorJames G Smirniotopoulos, MDProfessor of Radiology, Neurology, and Biomedical Informatics, Program

Director, Diagnostic Imaging Program, Center for Neuroscience and Regenerative Medicine (CNRM), UniformedServices University of the Health Sciences

James G Smirniotopoulos, MD is a member of the following medical societies: American College of Radiology,

American Roentgen Ray S ociety,American Society of Head and Neck Radiology,American S ociety ofNeuroradiology,Association of University Radiologists, Radiological Society of North America,American Societyof Pediatric Neuroradiology


Additional ContributorsBarton F Branstetter, IV, MDProfessor of Radiology, Otolaryngology, and Biomedical Informatics, University ofPittsburgh School of Medicine Chief of Neuroradiology, University of Pittsburgh Medical Center

Barton F Branstetter, IV, MD is a member of the following medical societies: American College of Radiology,

American Medical A ssociation,American Roentgen Ray S ociety,American Society of Head and Neck Radiology,American Society of Neuroradiology, Pennsylvania Medical Society, Radiological Society of North America


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Orbital Infection Imaging_ Overview, Computed Tomography, Magnetic Resonance Imaging