Imaging in Orbit and Oculoplasty

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Orbital Anatomy

Schematic diagram depicting orbital bony anatomy

The bony orbit is a quadrangular truncated pyramids situated between the anterior cranial fossa above and maxillary sinus below. Each orbit is formed by seven bones namely frontal, ethmoid, lacrimal, palatine, maxillary, zygomatic and sphenoid.[1]

Orbit is divided into various spaces and knowledge of these compartments are required for proper diagnosis of pathologies on imaging and for choosing the best approach to the tumours. Due to the characteristics of the types of tissue in each compartment, they have specifications within them. However, sometimes they may extend into more than one compartment. Here, we describe the various spaces and lesions specific to them[2]:

a) Extraconal Space: It is bound peripherally by periorbita, internally by four recti and anteriorly by septum. Common tumours in this space are lymphoma, capillary haemangioma, neoplasms of the lacrimal gland, and rarely by retinoblastoma, neurofibroma and metastasis. Tumors in this Space produce eccentric proptosis, can usually be palpated and best visualised on coronal section.

Schematic Diagram to show various orbital spaces in relation to orbital imaging

b)  Intraconal Space: It is called as muscular cone. It is the space bound by four recti muscles and their septum and anteriorly by tenons capsule lining the back of the eye. Optic nerve with sheath lies within it. Many circumscribed orbital tumours such as capillary haemangioma, solitary neurofibroma, varix, pseudotumor, lymphangioma occur in this space and are best studied in coronal planes. Parasagittal planes are used to study optic nerve but diameter of optic nerve and subarachnoid space are best described in coronal planes. Various optic nerve lesions in this space are optic nerve sheath meningioma, glioma, optic neuritis and fracture of orbital apex.

c) extra ocular muscle (EOM): Enlargement of extraocular muscles should be assessed by evaluating both sides in coronal section. Extraocular muscles are affected in various conditions like thyroid orbitopathy, myositis, pseudotumor. To differentiate between them axial or parasagittal cuts are required to know whether only muscle belly is enlarged or it is along with its tendon.

d) Lacrimal gland: Best assessed in coronal plane.

e) Subperiosteal space: It is a potential space between orbital bones and periorbita, limited anteriorly by the strong adhesions of periorbita to the orbital rim. Common lesions in this space are dermoid cyst, mucocoele, sub periosteal abscess, myeloma, osteoma, orbital fracture and fibrous dysplasia. Based on the location of the lesion all imaging planes are important in this particular space.

Orbital Imaging Techniques

X-Ray

The use of x-ray is limited to patients with trauma or suspected intra orbital foreign body. Standard views include PA view, lateral view and optic foramen view. In a true lateral radiograph, there should be superimposition of the floor of anterior cranial on both sides. For optic foramen and superior oblique fissure, Rheese projections are used.[3]

Ultrasound

It is non-invasive, cost-effective and easy to perform. It is an important first line investigation for evaluating intra ocular pathology especially in opaque media. It helps in differentiating cystic from solid lesions. It has two modes A scan and B scan. In normal eyes anterior and posterior chamber are cystic with echogenic lens present in between. Posterior to the globe, fat (echogenic) along with optic nerve sheath complex is seen as a central hypo echoic linear structure. Ultrasound has limited use in deep-seated lesions due to decreased resolution with depth. Also it is operator dependent. It is contraindicated in rupture of globe.[4]

Contrast enhanced ultrasound is micro bubble-based ultrasound with contrast agents helping in differentiating masses from pseudo masses (RD, haemorrhage).[5]

Colour Doppler

Helpful in evaluating blood flow in vascular lesions like vascular malformations, arterial/venous tumours, AVM & CCF.[6]

Computed Tomography (CT scan)

CT is an important modality of orbital imaging. It provides volumetric cross-sectional image acquisitions. It is useful for orbital trauma to assess bony fracture or extraocular muscles entrapment and in intra orbital foreign body localization.[7] It has an advantage over MRI in assessing orbital osseous lesions or soft tissue lesion which causes bony erosion, presence of calcification or to differentiate acute haemorrhage from mass lesions. It is also useful to evaluate anatomy of extraocular muscles and orbital apex in thyroid eye disease.[8]

Contrast enhanced CT is performed following intravenous administration of iodine rated contrast media like iohexol (omnipaque) & iodixanol (visipaque).[9] It is performed to evaluate different orbital lesions with different enhancement patterns. Enhancement is based on the blood flow and vascular permeability. It is done in mass lesions like tumours, vascular lesions like CCF pathologies of CNS, inflammatory lesions with optic nerve involvement, cellulitis & myocysticercosis.[10]

Magnetic Resonance Imaging (MRI)

MRI is based on the magnetic resonance properties of nuclear particles especially hydrogen in human body when placed in a strong external magnetic field. The probes with hydrogen atoms behave as tiny dipoles and get aligned along the direction of magnetic field, majority parallel (low energy state) and remaining few antiparallel high energy state. Following this, radio frequency is applied in which some atoms change directions from parallel to anti-parallel and reaches a state of excitation. When external radio frequency is switched off, they release energy and return to the pre-excited state, a process known as relaxation and is dependent on composition of tissue and environment in which the tissue is situated.[11]

Nowadays, MRI is the modality of choice as it provides higher soft issue resolution and tissue characterization, with better delineation of different orbital components. It helps in the diagnosis of neoplasm, vascular malformation, inflammatory disorders, and optic nerve lesions.

Diffusion Weighted Images (DWI) help in further characterization of orbital masses. It assesses random brownian motion of water molecules in a tissue and thus high cellularity lesions show limited diffusion and low ADC, like lymphomas. It also separates abscess which is more diffusion restriction from other inflammatory processes.[12]

MRI vs CT

MRI is the preferred imaging modality as it provides excellent soft tissue resolution of orbital contents, images the optic nerve along its entire course without any bony shadow and has no exposure of radiation. However, it is costly, requires the patient to lie still for a long time and is an absolute contraindication in magnetic intra orbital foreign bodies and cardiac pacemakers.[11]

CT is the ideal modality in bony pathologies, calcification, intraorbital foreign bodies and fracture. It is economical and requires a shorter duration of time. However, it has exposure of radiation specially in cases when required in repeated imaging and in children. It is also less sensitive for soft tissues, optic nerve, and cavernous sinus disorders.[8]

Orbital structure imaging requires slice thickness of 3 or 4mm and inter slice thickness of 0.5 to 1mm.

There are three type of cuts for imaging:

Axial – recognized by presence of both orbits in scan with brain tissue behind

Coronal – recognized by presence of both orbits in the scan with brain tissue above

Saggital – is the presence of only one orbit at a time with brain tissue above and behind.

Orbital Infections[13]

Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Image
Preseptal Cellulitis More common in < 5 years of age group Lid edema, redness CT- shows stranding, swelling, variable enhancement of the preseptal soft tissues anterior to the globe


MRI- the preseptal soft tissue demonstrates iso-intense T1 and hyperintense T2 signal

Sub Periosteal Abscess. Coronal contrast-enhanced CT image of right orbit showing extraconal marginally enhancing fluid collections located superonasally, consistent with subperiosteal abscess. These are present in continuation with opacified right ethmoidal air cells and right maxillary antrum with soft tissue density with hyperdense content.
Orbital Cellulitis More common in > 5 years of age group Proptosis, chemosis, limitation of EOM, fever CT- early- eyelid edema and sinusitis

Marked postcontrast enhancement.

Inflammation is seen in the medial or superomedial orbit adjacent to the opacified sinus, associated with fat stranding


MRI-orbital inflammation produce diffuse signal isointense to muscle. On T2 a fluid level may be visible as a layered hyperintense signal in an abscess or sinus.

Sub periosteal abscess[14] No age/gender predilection Collection of sub periosteal fluid causing abaxial proptosis along with other signs of cellutlitis CT- shows hypodense collection present along orbital wall


MRI- marginally enhancing fluid collection that shows restricted diffusion

Invasive Sino-orbital fungal disease[15] Immunocompromised (mucormycosis)

Imuunocompetent (aspergillosis)

Severe limitation of EOM with associated chemosis and blepharoptosis.

In mucormysosis, very acute progression of disease with presence of black nasal fliuid, eschar or skin discoloration (characteristic). On fundus examination, CRAO present.

In aspergillosis, sub acute progression.

CT- lobulated soft tissue msses, opacification of paranasal sinuses with high attenuation content  with enhancing adjacent orbital soft tissue


MRI -  superior to CT in identifying intraorbital and intracranial involvement

T1- low to high intensity T2- marked hypointensity

Invasive Sino-Orbital Fungal Disease. Axial non-contrast CT of right orbit shows an ill-defined lobulated mass of PNS (ethmoid) infiltrating into the orbit through the eroded medial wall, with high attenuation encircling the globe medially and indenting it.

Orbital Inflammatory Disease

Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other features Image
Thyroid Eye Disease[16] Young adults; Female > Male Axial Proptosis, Redness, watering, lateral flare, lid retraction, photophobia.

Restrictive myopathy

CT- spindle enlargement of EOMs occurs with relative normal tendinous insertion (coca-cola bottle sign).


MRI - Bulky EOMs are isointense on T1, slightly hyperintense on T2W images and show enhancement.

Most frequent involvement IR>MR>SR>LR. Superior Ophthalmic Vein may be enlarged due to apical compression
Axial and coronal section of non-contrast CT images of orbit showing three different patterns of TED. a)     Bilateral fusiform enlargement of the extraocular muscles sparing the tendinous insertion with posterior crowding (orange stars) b)    Bilateral fusiform enlargement of the extraocular muscles sparing the tendinous insertion along with increased orbital fat. c) Bilateral increased orbital fat (denoted by increase of hypodense areas of fat attenuation). EOM appears normal.
Myositis[17] Mean age 30-40 years Pain, ocular dysmotility, and redness.

EOMs involvment  is typically unilateral, painful, and rapid in onset (hours to days).

CT- diffuse enlargement of EOM involving tendinous insertion with inflammation in the adjacent fat.
IgG4 Orbital Disease[18] Mean age 40 - 55 years; Male : Females = 1.3:1 Painless unilateral or bilateral eyelid swelling, erythema, proptosis, associated dacroadenitis may be present. CT- nonspecific mass-like inflammation may involve any of the soft tissues of the orbit.

Bilateral, tendon sparing EOM enlargement, preferentially involving the lateral rectus muscles, as well as the lacrimal gland involvement .


MRI- significant hypointense signal on T1 and T2W images with marked post contrast enhancement

Most commonly affects lacrimal gland
IgG4 Orbital Disease. T2WI MRI of bilateral orbit showing hyperintense signal with involvement of lacrimal gland and lateral rectus and superior rectus muscle.
Wegners Polyangitis[19] Mean age 65-75 years Ocular pain, diplopia, decreased visual field with sign suggestive of URTI or lung infection. Imaging findings depend on orbital location, the extent of involvement and invasion into adjoining structures.

CT - show sinusitis and bony invasion

MRI - identifies granulomas and deliniates mucoid plugs.

Wegners Granulomatosis Polyangitis. Non-contrast axial CT images in soft tissue window showing left orbital large infiltrative extra- and intra-conal soft tissue masses that mould to the orbital contour associated with proptosis of the globe. Ipsilateral maxillary in the same case showed pansinusitis with medial wall sclerotic thickening.
Sarcoidosis[20] Bimodal presentation: 20-30 years and 50-60 years Abaxial proptosis; dacryoadenitis; restrictive myopathy; ocular involement may be present CT- Bilateral diffuse enhancement and enlargement of the lacrimal glands with infiltration of the adjacent fat.


MRI-  high T2 signal, thickening and enhancement of the optic nerve with linear enhancement of the optic nerve sheath (tram track sign).

Orbital Sarcoidosis. Axial non-enhanced CT image of orbit shows bilateral enlarged lacrimal gland with homogenous density. The patient also has bilateral mediastinal enlarged lymph nodes.
Pseudotumor Mean age group:40-50 years. Abrupt onset pain, abaxial proptosis, eyelids swelling, erythema CT - preferred modality.

Lacrimal gland diffusely enlarged with overall shape preserved.

EOM tubular configuration enlargement with tendon involving. (MR > SR> LR>IR).

Optic Nerve - non-enhanced optic nerve surrounded by inflammation (tramline sign).

Cavernous sinus - if involved best seen on MRI

Orbital Pseudotumor. a) Axial non-enhanced CT images with enlargement of the lateral rectus muscle. b)    Coronal contrast-enhanced CT image demonstrate enlargement of the right lateral rectus muscle with stranding of the adjacent fat

Tumors/Lesion

Extraocular

Extraocular lesions can be either transcompartmental, intraconal, or extraconal.

Transcompartmental

Such lesions occupying both extraconal and intraconal space. They can be benign or malignant.

Benign

Vascular
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other Features Image
Capillary Haemangioma[21] Present at birth during infancy, grows with the child say up to 5–7 years age, and disappear by 10 years Soft, non-tender, non-pulsatile ill-defined mass. Cutaneous discoloration or leash of vessels on the lids, periocular soft tissues.

Commonly located anterior to the globe in the eyelid.

USG Doppler Hyperechoic.


CT ill-defined to irregularly marginated, lobulated, infiltrating masses with moderate to marked contrast enhancement.


MRI – Best for characterization of hemangiomas.

T1- intermediate signal

T2- hyperintense

Proliferative phase intense early enhancement with multiple flow voids (characteristic)

Involuting phase - heterogeneous with fibro-fatty tissue, decreased vascularity  and less prominent enhancement.

Capillary Haemangioma. a & b) CE MRI (T1 weighted) of brain and orbit- Axial section showing well-defined lesion involving the left orbit with no intraconal extension, involving the medial rectus muscle. It shows heterogeneous enhancement with contrast. c & d) MRI brain and orbit (T2 weighted)- Axial and coronal section, the lesion shows hyperintensity.
Lymphangioma/ Venolymphatic Malformation[22] Children

(>50% are diagnosed at birth).

Painless progressive long standing proptosis in a child, often sudden increase following URTI or haemorrhage

On examination, irregular heterogeneous masses, which are poorly defined

USG- to evaluate its vascularity, and to separate its cystic and solid composition. Macrocysts appear as anechoic area separated by septae. Microcysts appear hyperechoic.


CT- heterogeneously hyperdense, multicompartment appearance. It has mild or no enhancement. Wall or septae may show patchy enhancement.


MRI- Microcysts appear as solid irregular masses. Macrocysts variable signal depending on fluid. cystic areas are variable on T1 and hyperintense on T2.

Larger lesions may cause bone remodelling with extension into preseptal or infratemporal fossa through the inferior orbital fissure.

Presence of fluid-fluid levels produced by haemorrhages (chocolate cyst) of various ages is pathognomonic.

Lymphangioma. a,c Macrocystic lymphatic malformation. Sagittal T1 WI of left orbit showing large cyst with hypointense signal and Axial T2 WI MRI showing large cyst with fluid-fluid levels (haemorrhagic content hyperintense on T2 signal (orange arrow) with septa of hypointense fluid) b) USG orbit demonstrates MIXED variant lymphatic malformation, with multiple cyst (orange circles) d) Saggital T2 WI MRI of orbit showing multiple cyst with hyperintesne signal (microcyst marked with white arrow)
Varices[23] 2nd and 3rd decade , M=F Painless, progressive proptosis that increases on stooping forward/ Valsalva.

Usually located in posterior orbit.

USG - for dynamic assessment.

It appears as intermittently anechoic lesion which on straining distends with flow.

CT- irregular, segmentally dilated or  smooth, variably enhancing lesion, which significantly increases in size with straining. It is useful to detect bony abnormality associated with it. Calcification may be seen.

MRI- On T1 hypo to hyperintense

T2 - hyperintense.

Orbital venous varix. T1WI MRI of right orbit shows a large extraconal mass with areas of hyperintense signal demonstrating a venous varix post embolization.
AV Malformations[24] Post traumatic, no age/ gender predilection Pulsatile mass in orbit with pulsatile proptosis. eyelid and conjunctival congestion present with bruit heard.

Usually found in the superior orbit.

CT and MRI helps in diagnosis and its extent.

CT Angiography - important for treatment planning. They show enlargement and rapid filling of the proximal arterial system with early drainage into distal venous outflow.

Orbital and Eyelid Arterio-Venous Malformation a) Magnetic Resonance Angiography TRICKS (Time-Resolved Imaging of Contrast KineticS) confirms mid and delayed arterial phase blushing of orbital and eyelid mass with dense contrast. b)    Digital Subtraction (DSA) images of right orbit showing large dural AVM with the engorged external carotid artery and its branches and early venous drainage.
Carotid-Cavernous Fistula[25] No age/ gender predilection Direct – sudden pulsatile exophthalmos, conjunctival chemosis, with dilated episcleral vessels and bruit.


Indirect - gradual proptosis, conjunctival congestion or glaucoma.

USG Doppler – shows increased velocity with reversal of blood flow direction, dilated Superior Ophthalmic Vein (SOV) and arterial pulsations.

CT/MRI - proptosis, EOM enlargement, dilated and tortuous SOV, with engorgement and early enhancement of the ipsilateral cavernous sinus.

CT Angiography- differentiate direct and indirect CCF but cerebral angiography is used for accurate diagnosis and intervention.

Traumatic carotid-cavernous fistula) Axial T2WI MRI of right orbit showing dilated superior ophthalmic vein along its whole course (orange arrow) b) Coronal T2WI MRI showing dilated superior ophthalmic vein (white dotted arrow) with engorgement of the extra ocular muscles compared to the contralateral normal side (orange arrows)
Mesenchymal
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other Features Image
Rhabdomyosarcoma[26] Mean age - 8 to 10 years, M>F Proptosis or upper lid mass with blepharoptosis

Pain only in advanced cases. Usually present in superonasal quadrant.

CT-  irregular, homogenous well-defined soft tissue extraconal masses isodense to EOM, but may be heterogenous due to focal haemorrhage. CT is important for bony involvement.


MRI-

T1- isointense to muscle

T2-hyperintense with areas of high T1 signal secondary to hemorrhage and necrosis.

It shows mild to moderate uniform enhancement.

MRI  is important for aggressive tumours  to know their intracranial extension and invasiveness in adjacent paranasal sinuses.

The tumor may conform to adjacent bony walls and orbital structures such as the globe.
Rhabdomyosarcoma. a) Axial T1WI contrast-enhanced MRI of left orbit showing a transcompartmental ill-defined mass with homogenous contrast enhancement (orange arrow) b) Axial T2WI MRI of the mass showing hyperintense signal (blue arrow)
Neuroblastoma[27] Mean age of presentation 2 years Proptosis (may be pulsatile) and swelling of lid (unilateral/ bilateral raccoon eyes). Abdominal features.

Can have ecchymosis, Horner’s syndrome. Usually involves Posterolateral orbital wall.

CT -  metastases appear as either circumscribed or ill defined, increased attenuation to muscle, may have small calcifications. It can invade adjacent structures.


MRI

T1- hypointesne

T2- heterogeneous due to hemorrhage or necrosis, and heterogeneously enhance post contrast.

Systemic imaging including CT/MRI abdomen and/or chest. MRI spine for paraspinal tumors
Metastatic Neuroblastoma a) Coronal contrast-enhanced CT of the right orbit demonstrates bilateral transcompartmental, heterogeneously enhancing ill-defined soft tissue masses with proptosis of both the globes. b) Coronal CT Abdomen demonstrates a heterogeneously enhancing, centrally necrotic, partially calcified mass arising from the left adrenal gland, associated with multiple adjacent enlarged retroperitoneal lymph nodes.
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Lacrimal Gland Tumors [28](Adenocystic Carcinoma/ Mucoepidermoid carcinoma) Middle aged adults Ocular pain, inferonasal dystopia, abaxial proptosis CT -  heterogeneous, irregular, infiltrative mass with poorly demarcated margins. Bony erosion and calcification is common. It shows marked and focal enhancement.
Adenocystic Carcinoma of Lacrimal Glanda) Coronal post-contrast CT demonstrate right lacrimal gland mass with mild heterogenous enhancement (blue arrow) with orbital roof erosion and inferior globe dystopia (orange arrow) with b) areas of calcification (blue arrow).
Lymphoproliferative disorders[29]

--Lymphoma (most common), lymphoid hyperplasia and atypical lymphoid hyperplasia, and ocular adnexal lymphoma.

Elderly Minimal or no pain and with gradual progression. Usually bilateral. CT-  homogenous hyperdense lacrimal gland mass. Bony destruction is usually absent

MRI -

T1- isointense

T2-hypointense to muscle.

Marked enhancement post contrast.

Lymphoma. Axial non-contrast CT image showing left-sided enlargement of lacrimal gland with left intraorbital, transcompartmental hyperdense masses in an elderly male.

Intraconal

Benign

Vascular
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Image
Cavernous Haemangioma/ Solitary Encapsulated Venolymphatic malformation

(SEVLM)[30]

Middle age, Female Painless, progressive proptosis well-defined (pathologically encapsulated), oval to round USG- well circumscribed lesion, medium to high internal reflectivity and absent internal flow.


CT – well circumscribed, ovoid homogenous lesions. Usually shows moderate enhancement that increases with later phases.

MRI- hypointense relative to muscle on T1, hyperintense on T2.

Cavernous Haemangioma. a) Axial T1WI MRI shows a left intraconal ovoid, well encapsulated soft tissue mass that indents the posterior aspect of the eye globe associated with mild proptosis. b)Post contrast axial T1WI with fat suppression demonstrates progressive heterogeneous bright enhancement (white arrow) of the lesion c) USG orbit (B/A) showing a well encapsulated mass on B scan (orange circle) with corresponding internal acoustic reflections on A scan showing characteristic dancing spikes demonstrating rise and fall of waves as it traverses through multiple blood-filled channels within the tumor (blue arrows)
Neural
Type Age/Sex Predeliction Clinical Presentation Imaging Findings Other features Image
Optic Nerve Glioma[31] 1st decade Decreased visual activity, visual field defect, proptosis, and relative afferent pupillary defect The optic nerve cannot be seen separate from the mass; hence, the nerve appears tubular, tortuous, and kinked.

NF associated Gliomas-

On CT - hypodense and poorly-defined masses. Minimal or no enhancement is seen .

Sporadic Gliomas- solid cystic appearance.


MRI- CE MRI is investigation of choice. Generally T1 is iso/hypointense, T2 is hyperintense to cerebral cortex and shows variable contrast enhancement.(lesser than meningioma)

NF-1 glioma- bilateral optic nerve gliomas with intracranial involvement (diffuse enlargement of the chasm).

Sporadic- unilateral fusiform enlargement of the optic nerve. Intracranially, there is chiasmatic-hypothalamic mass with central cystic component.

Optic Nerve Glioma. a) Axial T1WI MR images demonstrate right optic nerve globular shaped mass of hypointense T1 and b) hyperintense T2 signal with mild post-contrast enhancement (orange and blue arrows). The optic nerve cannot be made out separately. Note the presence of a small area of cystic degeneration inside the lesion (blue arrow).
Optic Nerve Sheath Meningioma[32] 5th decade, F>M Insidious vision loss over months to years.


Triad – Vision loss, optic atrophy and optociliary shunt vessels on fundoscopy.

CT- smooth tubular thickening of the ON - iso to hyperdense and show calcification in 20–50% of cases. There is marked and homogeneous contrast enhancement.


MRI - isointense signals on T1- with respect to normal optic nerve.

T2 - heterogeneous and varies from slightly hypointense to slightly hyperintense.

Contrast-enhanced T1W images with fat suppression demonstrate a diffuse  tubular enhancing lesion around the optic nerve with characteristic tram track sign on axial images and target sign/doughnut  on coronal images
Optic Nerve Sheath Meningioma. a) Axial CT image shows an intraconal homogenous mass involving the intraorbital portions of the right optic nerve with optic nerve seen separately with typical tram track sign (dotted lines) seen on sagittal section (b)
Optic Neuritis[33] Papilitis

(children)

Retrobulbar neuritis (young adults)

Unilateral rapid onset of vision loss. Eye pain worsen with movements. CT has no role

MRI - increased signal and bulk of the nerve

Evaluate MRI brain for periventricular plaques
Optic Neuritis. a)T1WI contrast-enhanced MRI Brain and Orbit showing bilateral prominent optic nerve Enhancement (left > right) with (b) both cerebral hemispheres and the left middle cerebral peduncle shows multiple areas of demyelination.

Extraconal

Benign

Vascular

Lesions in this space may include cavernous haemangioma, venolymphatic malformations, capillary haemangiomas.

Neural
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other features
Schwannoma[34] 20-40 years mean age group Painless, progressive proptosis with diplopia Schwannomas have a heterogeneous T2 signal and variable patterns of enhancement with homogeneous or ring enhancement being most common. Orbital schwannomas can show delayed homogeneous enhancement like cavernous malformations, but do not follow the centripetal enhancement pattern of the latter.
Mesenchymal
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other features Image
Dermoid Cyst[35] Child or young adult Round to oval well defined  slow growing mass near the frontozygomatic/frontoethmoidal suture.

Intraorbital dermoid often cause proptosis with globe dystopia.

USG- capsulated well circumscribed lesions with variable internal reflectivity due to areas of calcification within.

CT- They have cystic center with areas of fat within and appear hypodense. A fat–fluid level and calcified rim may be present. Denser foci within the lesion represent flecks of keratin and sebum.

MRI- Lesion tends to be heterogeneously hyperintense on T2WI and hypointense on T1WI.

External – superotemporal

Internal – supero nasal

Orbital - superotemporal

Dermoid Cyst. a) Contrast-enhanced CT image (bone window) showing well-defined, low attenuation, non-enhancing, subcutaneous hypodense fat density lesion seen at medial canthal region with scalloping (red arrow) of adjacent nasal none.
Lipoma[36] Any age group Mostly asymptomatic untill large. It arises mainly from the anterior orbit. On CT scan, typically lipoma appears as distinctive low attenuation lesion sometimes with a finely defined border. On MRI, it is hyperintense on T1 weighted image. However, it does not enhance after contrast.
Orbital lipoma. Non-contrast CT of the left orbit showing well defined intraconal mass which is hypodense and has fat attenuation with no bony changes.
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Hydatid Cyst[37] Any age group Abaxial Proptosis. Chemosis, lid edema, restriction of EOM, visual impairment Well defined, thin walled, oval lesion with peripheral rim enhancement of their capsule.


CT - uni/multi loculated with few areas of calcification may be present.


MRI

T1 - hypointense

T2 - Hyperintense

USG - double layer sign, water lily sign.

MRI spectroscopy can be performed

Hydatid Cyst. a) Coronal non contrast CT of right orbit showing round, well-defined lesion with fluid density with hyperdense rim and septa running through the cyst b) USG double wall sign (orange arrows), with daughter cyst.
Lacrimal gland tumor
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other features Image
Pleomorphic Adenoma[38][38] 40-55 years Indolent painless enlargement of the gland causing proptosis and characteristic S-shaped ptosis CT- well circumscribed homogenous mass in lacrimal fossa with bony scalloping.

MRI-  bright enhancement.

T1- hypo/iso intense

T2- hyperintense

Bone remodelling may be present but no bony erosion.
Pleomorphic Adenoma. a & b). Non-contrast CT scan demonstrates well-defined, round to oval lesions, smooth in outline, associated with prominent scalloped lacrimal fossa (orange curved line) formation due to pressure without bone erosion in comparison to left orbit (orange arrows). Long-standing large tumours lobulations and radiolucent areas of cystic degeneration.
Bony lesions
Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other Features Image
Langerhans Cell Histiocytosis[39] Early childhood Abaxial proptosis, bony defect with orbital infiltration of lesion. Usually present at superotemporal orbit/sphenoid wing CT- soft tissue homogenous mass with hyperdense margin.

MRI- T1 intermediate signal, T2- hypointense relative to bone marrow fat.

File:LCH.jpg
Sphenoid wing Menigioma[40] 50-60 years; Caucassian Female Depends on location of primary tumor. Orbital mass/temporal mass/sella tursica. CT-  intraosseous part appears as bone hyperostosis and expansion

MRI- there is increase in the dark signal of the bone (extremely hypointense on T2).

Meningiomas of the greater wing of sphenoid cause intraosseous growth, which may cause narrowing of intraorbital foramina. File:Figure 5 SWM.jpg
Fibrous cell dysplasia[41] Less than 30 years age Non-specific CT, characteristic expansile bony lesion with ground glass density is seen.


MRI

T1 isointense

T2 hypointense because of sclerosis and fibrous stroma.

Ossifying fibroma mimics them on CT, but they have borders better defined than FD.
Coronal and axial CT images reveal an expansile bone lesion with a typical ground glass appearance involving the left orbital roof and zygomatic bones. There is an encroachment on the orbital cavity.
Dumbell dermoid cyst[42] 10-30 years C chewing oscillops (characteristic sign) iawhi h is caused by a synkinetic movement of the temporallis muscle associated with pursing of the lips during chewing. CT scan demonstrates a mass lesion that straddles the lateral orbital wall (mostly). A bony channel in the lateral orbital wall connects the two lobes. The deep lobe displaces many of the lateral intraorbital structures.
Dumbell Dermoid Cyst. a) Coronal T1WI MRI of left orbit showing an extraconal cystic heterogenous mass w with a communicating mass under the temporalis muscle. b) Axial CT scan arrowhead shows the cyst penetrating the bone at the frontal zygomatic structure.

Malignant

Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other Features Image

Haemangiopericytoma/ Solitary Fibrous Tumor (SFT)[43]

No age/sex predeliction Proptosis, painless. Extraconal location most commonly along the paranasal sinuses. Extraconal location most commonly along the paranasal sinuses CT- homogeneous to heterogeneous, rounded or elongated masses of moderate density, smooth, well circumscribed. Calcification in 25% cases. Enhancement is moderate to marked.

MRI - round to oval tumour, well defined borders.

T1 - the signal is isointense to muscle, and hypointense to fat.

T2 - the lesion is hyperintense to fat.

Dynamic CT may show prominent early enhancement with rapid washout.
Hemangiopericytoma. Contrast-enhanced CT image of right orbit demonstrates a well-defined, round, heterogeneously contrast-enhancing mass located extraconally in the medial orbit. It is isodense to extraocular muscle.

Intraocular

Ultrasound should be the first-line radiologic modality for the evaluation of suspected intraocular masses, and MRI later.

Lesion Age/Sex Predeliction Clinical Presentation Imaging Findings Other features Image
Retinoblastoma[44] Children White reflex or strabismus. Most common intraocular tumor of childhood. USG and MRI to distinguish RB from other causes of white reflex.

USG- evaluate calcification


MRI- preferred for delineating the morphology and extent of the tumor, especially extraocular spread and optic nerve involvement. Has low T2 signal.

CT- Radiation risk

Retinoblastoma. a) Contrast-enhanced T1WI axial MRI image showing an enhancing right intraocular mass with no extraocular extension (orange arrow) b) T2WI axial MRI image showing hypointense signal (blue arrow) c) USG (B/A) showing intraocular mass lesion with specks of calcification corresponding to the spikes of A-scan.
Uveal Melanoma[45] Middle aged adults Dimunition of vision, assoicated with exudative retinal detachment. MRI is the investigation of choice.

T1 hyperintensity

T2- hypointense

It enhances brightly on contrast

Uveal Melanoma. a) Axial contrast-enhanced T1WI MRI with a polypoidal right intraocular mass, a uveal melanoma, with hypointense signal on T2WI (b)

Lacrimal System

Dacrocystography (DCG)

a) Macro- DCG showing left sided common canalicular obstruction. b-d)Micro CT-DCG showing b) right sided lower proximal canalicular obstruction, c) common canalicular obstruction ,and d) distal nasolacrimal duct obstruction

For anatomic evaluation of the lacrimal system. It tells us about the exact level of obstruction or stenosis and the presence of diverticulum, fistula, stones, or tumours. CT-DCG show adjacent bony structures also. During the procedure, dye is injected into bilateral lacrimal systems and magnified images then are obtained.[46] There are two types :

Macro DCG

X-Ray based. An erect scan delayed by 5 minutes post injection of contrast is taken.

Micro DCG

Computed tomography (CT-DCG)/magnetic resonance imaging (MRI-DCG) scan based.

Dacrosynctigraphy (DSG)

For physiologic evaluation of the lacrimal system. It is a noninvasive test. Radiolabelled Tc99m is instilled into conjunctival cul-de-sac, while a modified gamma camera records images over 20 minutes. It is used for identification of the location of a partial or functional block, such as conjunctivochalasis or punctal occlusion.[47]

Orbital Trauma[47]

Fractures[48]

Lesion Clinical Presentation Imaging Findings Image
Orbital floor Can be associated with entrapment of Inferior rectus or intraorbital fat, enophthalmos.

In children, due to resilient bones, there is often a minimal bony displacement and herniation of orbital contents but inferior rectus may still get entrapped.

Non-contrast CT – preferred for fractures and detailed bony imaging.

Diffuse hyperdense - Bleed


Air pocket – emphysema


EOM - orbital wall fractures with muscle entrapments (trapdoor fracture)


Axial scan- for medial and lateral orbital wall, zygomatic arches, maxillary antrum

Coronal scan - orbital floor and roof, orbital rim, cribriform plate, and the skull base.

Saggital oblique scan- orbital apex and optic canal fractures.

Blow out Orbital Floor Fracture. a) Sagittal and coronal reformatted CT images demonstrate fracture of right orbital floor with inferior displacement of the fracture segment and entrapment of the inferior rectus muscle (orange arrow) b) Trapped door fracture showing trapped muscle (blue arrow)by the self-realigned fracture fragments (orange circle) in children.
Medial wall Usually along with inferior wall fracture. On CT normal posterior-medial bulge is lost.
Superior wall Best on coronal section. It can be associated with CSF leaks, intracranial haematoma or pnemocephalus.
Saggital non-contrast CT image of right orbit showing roof blow out fracture
Zygomaticomaxillary complex Fracture involves lateral and inferior orbital walls and up to zygomatic arch.
Zygomaticomaxillary complex fracture. a, b Coronal and Axial CT images demonstrate fracture of the lateral and inferior orbital (orange arrows) wall and left zygoma (blue arrow), with angulation of the lateral orbital wall. c) 3D reconstructed CT image showing tripod points of the fracture (white arrows)
NOE Marked comminution of the nasal bones bilaterally and the septum, medial orbital wall and ethmoid sinuses including the cribriform plate
Bilateral NOe complex fracture. Axial non-enhanced CT image demonstrates bilateral multiple comminuted fractures of the Nasal bones, medial wall of both Orbits and Ethmoid air cells with fracture of nasal septum
Le Fort Le Fort fracture II & III is related to orbit.

II- Pyramidal fracture, fracture line extends inferolaterally from the nasofrontal suture  through the medial and inferior (exclusive to it) orbital walls.


III - Transverse fracture extends from the naso-frontal suture laterally and through the medial and lateral orbital walls, as well as the zygomatic arches.

Le Fort II a) Axial and b) coronal reformatted CT images (bone window) demonstrate fracture of both pterygoid plates (orange circles), with bilateral fractures of inferior orbital walls (blue stars) and inferolateral maxillary sinuses walls.

Foreign body[49]

Imaging should be done in cases with wooden foreign body to know the exact size, shape and location of the foreign body. Intra-orbital wooden foreign body is not visible on X-ray orbit due to its radiolucent property. Diagnosis of intraorbital wooden foreign body on B-scan ultrasonography needs expertise, and very deep foreign body may be missed. MRI-scan is the imaging modality of choice for the diagnosis of intraorbital wooden foreign body. Intra-orbital wooden foreign body can be seen better in MRI scan because density of protons and their relaxation time in the wood are different from the orbital soft tissue. The wooden foreign body appears hypo-intense as compared to the orbital fat on T1 and T2. The appearance of intra-orbital wooden foreign body on CT-scan varies with the time according to the degree of the hydration. In the acute stage, a wooden foreign body is seen as a continuous linear track of air because its density is similar to the air. In the sub-acute stage, because of the increased hydration, the density of wooden foreign body becomes similar to the orbital fat, making the diagnosis difficult. In chronic stages, its density is more than the orbital fat.[49]

Orbital Hemorrhage[50]

Age/Sex Predeliction Clinical Presentation Location Imaging Findings Image
Non specific; M> F (more trauma in males) Acute onset proptosis, with ecchymosis and limitaion of EOM. Retrobular, subperiosteal On CT, hemorrhage is identified as an ill-defined high attenuation of the soft tissues.


On MRI, acute hemorrhage demonstrates hyperintense signal on T1W images.

Orbital Hemmorhage. Coronal non contrast CT of right orbit showing well defined high attenuation sub periosteal hematoma indenting and displacing the globe inferiorly.

Imaging after Oculoplasty Surgery

Axial and 3D reconstructed CT images of left orbit showing post operative orbital floor and rim implant for orbital fracture
Axial non-contrast CT of left orbit showing superiorly migrated implant post enucleation surgery for retinoblastoma

At times, post operative imaging is also required for confirming the adequate position of implants.[51] This may be done for post orbital fracture repairs with inadequate cosmesis to look for residual enophthalmos, post enucleation for a migrated impant, post surgery for anophthalmic socket with tissue expander and post surgery for lid retraction with metallic weights.

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