Orbital Infection Imaging 

Updated: May 30, 2019
Author: Claudia F E Kirsch, MD; Chief Editor: James G Smirniotopoulos, MD 

Practice Essentials

When 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 considered separately from the globe. The globe is contained by the sclera and lies within the fascial envelope of the Tenon capsule. Orbital cellulitis, an orbital infection resulting from a sinus infection,[3, 4, 3, 5, 6] is seen in the image below. 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 the assessment of these disease entities, although dedicated ophthalmic ultrasonography may be a useful adjuvant.[7]

Orbital cellulitis is rare but potentially severe in children. Diagnosis is primarily based on clinical examination and imaging (CT or MRI). In sinonasal-related orbital infection, posterior septal complications can be especially dangerous in children, in that they may lead to loss of vision (due to optic neuritis or orbital nerve ischemia) and even become life-threatening (eg, intracranial abscess and cavernous sinus thrombosis). They are therefore considered ophthalmic emergencies.[8, 9, 6, 10, 11, 12]  

Axial computed tomography scan of orbital and faci Axial computed tomography scan of orbital and facial cellulitis.

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.[13] Chandler et al defined the following categories of orbital infections (images of which are presented below)[14, 9] :

  • I. Inflammation with edema

  • II. Orbital cellulitis

  • III. Subperiosteal abscess (SPA)[4]

  • IV. Orbital abscess

  • V. Cavernous sinus thrombosis

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

One of the most important clinical and radiographic questions regarding these categories is whether the orbital infection is preseptal or postseptal.[15, 11]

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

Axial postcontrast CT scan of a 56-year-old woman Axial postcontrast CT scan of a 56-year-old woman with concern for orbital infection. Note the left orbital proptosis; there are both preseptal and postseptal inflammatory changes, with stranding of the left intraconal fat planes. In this patient, the diagnosis was mucormycosis and was highly worrisome for angioinvasive spread to the cavernous sinus, which can lead to cavernous sinus thrombosis.
Same patient as in the axial image (56-year-old wo 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 sinus thrombosis.
MRI (1.5 Tesla) of the same patient (56-year-old w 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 the course 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 worrisome for continued angioinvasive spread of the mucormycosis into the left lateral pons.
MRI (1.5 Tesla) of the same patient (56-year-old w 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 the course 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 worrisome for continued angioinvasive spread of the mucormycosis into the left lateral pons.
MRI (1.5 Tesla) of the same patient (56-year-old w 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 the course 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 worrisome for continued angioinvasive spread of the mucormycosis into the left lateral pons.
MRI (1.5 Tesla) of the same patient (56-year-old w 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 course of the cisternal segment of the left trigeminal nerve, with progression of the associated restricted diffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci of restricted diffusion are now noted along the left medial temporal lobe, which are worrisome for continued progression of disease and the development of new areas of ischemic change.
MRI (1.5 Tesla) of the same patient (56-year-old w 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 course of the cisternal segment of the left trigeminal nerve, with progression of the associated restricted diffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci of restricted diffusion are now noted along the left medial temporal lobe, which are worrisome for continued progression of disease and the development of new areas of ischemic change.
MRI (1.5-Tesla) of the same patient (56-year-old w 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 course of the cisternal segment of the left trigeminal nerve, with progression of the associated restricted diffusion, with increased fluid attenuated inversion recovery (FLAIR) signal along the left lateral pons. Redemonstration of a left cavernous sinus thrombosis is seen. New abnormal foci of restricted diffusion are now noted along the left medial temporal lobe, which are worrisome for continued progression of disease and the development of new areas of ischemic change.

Preferred examination

CT scanning is often the first imaging modality that is used because of its ease and availability at most medical institutions.[16, 17, 18]  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. When 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 a subperiosteal abscess (SPA). CT scanning is also usually the first imaging modality of choice to identify an SPA, which may be located just lateral to the lamina papyracea. Although CT scanning is useful, repeated scans can be damaging to the lens. Thus, imaging studies should be tailored appropriately.[19, 8, 9, 10, 12, 20]

CT scanning and MRI may be helpful in distinguishing an endophthalmitis with limited secondary extraocular inflammation from a true panophthalmitis with infected orbital tissue. In addition, diffusion-weighted imaging (DWI) on MRI shows utility in assessing the optic nerves for developing ischemia or infarction, which may occur during orbital infections. 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 between diseased tissue and normal tissue; specifically, it allows one to identify intracranial dissemination of infection or cerebral infarction.[21, 22]  

In pediatric patients, ophthalmic ultrasonography, in skilled hands, may be a useful adjuvant for the rapid evaluation of preseptal versus postseptal involvement, as well as 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.[7, 23]

MRI, especially postgadolinium-enhanced, fat-suppressed sequences, is useful for the 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.[24]

(See the images below.)

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

MRI is also useful for assessing intracranial extension of the infection into the cavernous sinus and for evaluating cavernous sinus thrombosis. DWI in MRI can help in the assessment of the optic nerves for developing ischemia or infarction, which can occur secondarily from orbital infections.[21, 22]

MRI may be useful for evaluating immunocompromised patients who have viral infections. 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 optic nerves and radiations, and this modality may demonstrate T2-weighted hyperintensity and contrast enhancement that extends along the optic nerves, optic tracts, lateral geniculate bodies, optic radiations, and optic cortex.[16]

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 be diagnosed 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 orbital abscess 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).[25]

Kapur et al identified the role of DWI in differentiating orbital inflammatory syndrome, orbital lymphoid lesions, and orbital cellulitis. The authors found a significant 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 than orbital inflammatory syndrome and that orbital inflammatory syndrome lesions were significantly brighter than cellulitis. In addition, lymphoid lesions showed lower ADC than orbital inflammatory syndrome and cellulitis, and a trend was seen toward lower ADC in orbital inflammatory syndrome than in cellulitis.[26]

Limitations of MRI include the length of time that is needed to obtain the images and 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 to perform MRI in patients with pacemakers, nonapproved aneurysm clips, or other devices that are not approved for placement in the MRI scanner are additional limitations.

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

Adjacent tissue may be involved either primarily or secondarily in orbital infections, 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 Coronal computed tomography scan of a patient who was on steroids and had multiple myeloma. In addition, the patient had infectious dacryoadenitis with Staphylococcus aureus infection and an abscess collection.
Coronal computed tomography scan of a patient with Coronal computed tomography scan of a patient with dacryoadenitis and Staphylococcus aureus infection, resulting in an abscess.

A diagnosis of dacryocystitis is made clinically unless adjacent periorbital cellulitis is present, limiting the ophthalmologic evaluation. Because the lacrimal sac is a preseptal structure, radiographic imaging in patients with periorbital cellulitis is a helpful adjuvant. If only the lacrimal gland is infected and inflamed, the treatment is nonsurgical because of the preseptal location. However, extension into the postseptal space with a resultant abscess may require surgical treatment.[27, 28]

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

Nuclear medicine images that use technetium-99m (99mTc)–labeled leukocytes have been useful in the diagnosis of orbital implant infections in patients in whom CT scans failed to reveal radiographic abnormalities.[29]

American College of Radiology Appropriateness Criteria

The ACR has published guidelines on imaging for orbital infection, including the following[20] :

  • Patients presenting with symptoms and signs of orbital cellulitis (postseptal cellulitis) are often referred for imaging to assess for complications including intra-orbital abscess, intracranial involvement, and vascular compromise. The source of this infection is often from the adjacent paranasal sinuses and may be viral, bacterial, or fungal.
  • Idiopathic orbital inflammatory syndrome (IOIS), IgG4-related orbital disease, and other inflammatory or granulomatous processes are potential clinical and imaging mimics for orbital cellulitis. IOIS, previously known as orbital pseudotumor, may present with signs and symptoms that mimic infection and is a diagnosis of exclusion. IgG4-related orbital disease is a relatively recently described inflammatory condition that may account for a significant percentage of patients that have been previously described as idiopathic. Manifestations include eyelid or periocular swelling, lacrimal gland enlargement, extraocular muscle involvement, intra-orbital mass, proptosis, and cranial nerve V involvement.
  • CT of the orbits with contrast is often the initial imaging modality in the emergent setting for suspected infection.
  • CT is superior to MRI for foreign body assessment, calcification detection, and osseous evaluation.
  • CT can be used in conjunction with the Chandler criteria to evaluate for the presence of bone erosion and subperiosteal abscess, which may require surgical intervention.
  • Imaging findings may show bone erosion on CT, opacification of a neighboring infected sinus, or intra-orbital extension of inflammatory disease.
  • In patients who cannot receive contrast, a noncontrast orbit CT may still add useful information. Precontrast and postcontrast imaging is typically not necessary in evaluating these patients because the precontrast images do not add significant diagnostic information in this scenario.
  • Orbital MRI is complementary to CT in evaluating intra-orbital spread of infection. An MRI of the orbits without and with contrast should be considered if a more detailed assessment of intra-orbital spread of infection is clinically warranted.
  • In patients with suspected intracranial extension or complications, an MRI of the brain with high-resolution images to include the cavernous sinuses provides greater soft-tissue resolution than CT. A high index of suspicion and low threshold for MRI is needed if invasive fungal infection is of concern in an immunocompromised patient because of the morbidity of the disease. Although contrast is preferred, in patients who cannot receive contrast, a noncontrast orbital MRI may provide useful information.
  • Orbital MRI is complementary to orbital CT in evaluating patients for IOIS, IgG4-related orbital disease, or other inflammatory or granulomatous disease. Currently there is little evidence to support one modality’s superiority to others in evaluating this patient population. A hallmark of IOIS in its chronic form is fibrosis, which results in decreased signal on T2-weighted MRI sequences.
  • CTA or MRA may be added to routine CT or MRI scans if there is a suspicion for vascular invasion including cavernous sinus thrombosis, particularly in the setting of fungal disease. MRA may be performed without or with contrast. In the setting of cavernous sinus thrombosis, a contrast-enhanced MRA may provide additional information not provided by a traditional noncontrast MRA examination. There is a limited role for DSA in evaluating patients with orbital infection.

 

 

Computed Tomography

CT scanning is an extremely useful imaging modality in the setting of orbital infections, especially in detecting subperiosteal abscesses (SPAs), and is often the first imaging modality that is used because of its ease and availability at most medical institutions.[16, 17, 18]  [19, 8, 9, 10, 12, 20] Orbital cellulitis is usually well visualized because 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 faci Axial computed tomography scan of orbital and facial cellulitis.
Axial computed tomography scan of orbital and faci Axial computed tomography scan of orbital and facial cellulitis.
Coronal computed tomography scan in a pediatric pa Coronal computed tomography scan in a pediatric patient with sinusitis as well as an orbital and subperiosteal abscess.
Axial computed tomography scan in a patient with a Axial computed tomography scan in a patient with an infection caused by Streptococcus pneumoniae and a superior orbital subperiosteal abscess that resulted in blindness.
Axial computed tomography scan in a patient with a Axial computed tomography scan in a patient with an infection caused by Streptococcus pneumoniae and a superior orbital subperiosteal abscess.

On CT scans, preseptal cellulitis may appear as an area of increased density within the low-density orbital fat. This may represent the first sign of infection, in which there is obliteration of the normal fat planes and swelling of the anterior orbital soft tissues.

As the cellulitis progresses, more discrete densities within the orbital fat may appear. Cellulitis is usually confined to the extraconal space; however, if the infection is allowed to progress, it can enter the muscle cone, resulting in an intraconal 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 to the lamina papyracea.[30]

Although CT scanning is an excellent imaging modality for identifying preseptal cellulitis, SPAs, defects within the lamina papyracea, and dehiscence of the bony margins 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 the region.[30, 17]

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

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

Magnetic Resonance Imaging

MRI is commonly used to assess orbital and soft-tissue disease[31] and has advantages 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 advantageous in evaluating any infectious process that extends from the orbital apex to the cavernous sinus. The superior ophthalmic vein and cavernous sinus may be assessed noninvasively by evaluating the vascular flow via gradient-echo imaging.[24]

On MRI, an orbital cellulitis appears hypointense on T1-weighted images and hyperintense on T2-weighted images.[19]

Although T1-weighted images demonstrate the normal findings of high signal intensity of orbital fat with dark inflammatory changes, and although T2-weighted images 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.[32]

MRI is especially useful in patients who have an aggressive fungal sinusitis, such as mucormycosis and aspergillosis, which has a propensity for extension into the orbit, cavernous sinus, and neurovascular structures. (Fungal sinusitis is exhibited in the MRI scans below.) Mucormycosis is markedly angioinvasive; the fungus grows into the internal elastic membrane of the blood vessels. The fungal hyphae may then extend into and occlude the lumina of the blood vessels they have invaded.

Coronal T1-weighted, postgadolinium, fat-saturated Coronal T1-weighted, postgadolinium, fat-saturated magnetic resonance image in a patient with allergic fungal sinusitis, with extension into the orbit.
Coronal T2-weighted magnetic resonance image of a Coronal T2-weighted magnetic resonance image of a patient with allergic fungal sinusitis and extension into the orbit.
Axial T1-weighted, postgadolinium magnetic resonan Axial T1-weighted, postgadolinium magnetic resonance image in a patient with sino-orbital and cavernous 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.[21, 22]

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). NSF/NFD has occurred in patients with moderate to end-stage renal disease after being 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 of the 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 ribs; and muscle weakness.

 

Ultrasonography

Ultrasonography is usually performed in ophthalmology practices by trained technicians using a high-frequency 10-MHz probe. The probe is applied over a closed eyelid, with the glove in a neutral position and with gentle eye motions from left to right.[23]

To assess the posterior aspect of the globe, the gain settings are adjusted to dampen near-field echoes. To assess the vitreous and central portion of the globe, the 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 an echogenic 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.[33]

Ultrasonography requires a dedicated ophthalmologic technician and may not allow important visualizations of the cavernous sinus and the intracranial extension of infections.