We can classify the orbital pathology as:

1. Post-Traumatic pathology:

1.1 Orbital wall fractures

The orbit is delimited by four bony walls, the superior, medial, inferior and lateral, consisting of a total of eight bones. They are classified according to the involvement or not of the orbital rim, and in the absence of involvement, of the displacement of the bony fragments outwards or into the orbit (blow-out and blow-in respectively). [1]

Fig 1: Representation of orbital fractures and their most basic classification.

In these cases it is important to describe the type of fracture, if there is herniation of the orbital fat through the fracture or if there is entrapment of the extraocular muscles, as well as to evaluate possible eye involvement (breakage, haematomas, foreign bodies...). Other post-traumatic findings to rule out include carotid-cavernous fistula, discussed below. [2]

Fig 2: 20-year-old patient who came to the emergency department for an assault. CT scan shows a blow-out fracture of the orbital floor (circle) with herniation and entrapment of the inferior rectus muscle (arrow).

1.2 Globe rupture

Ocular trauma is the main cause of visual acuity loss in young individuals. One of its possible outcomes is globe rupture, an ophthalmological emergency. In blunt trauma ruptures are most common immediately following insertion of the rectus muscles. [3]

Fig 3: A 57-year-old patient presented with an incised contused injury to the left eye. The CT images show a disarrangement of the ocular morphology (flat tyre sign) and a small metallic foreign body inside the eye.

A number of different findings are identified in CT:

• Loss of the rounded morphology of the eyeball (flat tyre)
• Presence of foreign bodies or intraocular gas
• Thickening of the posterior sclera
• Blurring of the eyeball margins

1.3 Orbital foreign body

A thorough evaluation is necessary to rule out foreign bodies, as their density varies greatly depending on their composition from >1000 HU (metal or glass) to -600 HU (wood). [4]

2. Tumoral:

Orbital masses have a wide differential, and a correct description of the tumour is essential to narrow it down to the most probable pathologies. They can be classified into three main compartments: intraconal, extraconal and intraocular.

2.1 Lymphoma

Primary ocular lymphoma is the most common orbital tumour, accounting for up to 50% of malignant orbital lesions. It usually affects people between 50 and 70 years of age, with a predilection for the female sex, and up to 17% of cases are bilateral. [5]

Fig 4: 85-year-old patient with suspected carotid-cavernous fistula due to conjunctival hyperhaemia of 9 months of evolution. CT scan showed a 4-mm lateral nodular thickening in contact with the posterior wall of the eyeball, lateral to the optic nerve. This lesion shows enhancement after contrast administration (CT scan - arrows and MRI T1 Gadolinium - arrowhead).

In imaging: CT scans show a homogeneous, isodense or slightly hyperdense mass with the extraocular musculature and discrete enhancement after contrast administration. MRI shows similar characteristics to cerebral lymphomas:

• T1: iso/hypointense with respect to the muscles, and with homogeneous enhancement after gadolinium administration
• T2: iso/hyperintense with respect to the muscles
• DWI/ADC: diffusion restriction 

2.2 Melanoma

Orbital melanoma may be primary, due to local extension from the uvea, conjunctiva or eyelid, or due to metastatic disease. Primary melanomas are extremely rare (<1% of orbital neoplasms), as opposed to uveal melanomas (which represent the most frequent primary intraocular tumour). They account for up to 20% of secondary/metastatic tumours of the orbit. [6]

Fig 5: 88-year-old patient who came to the emergency room with headache for which a CT scan was performed. The CT scan showed thickening of the superonasal retina, and the study was later extended with MRI. On MRI this thickening was hyperintense on T1 and hypointense on T2, findings compatible with melanoma.

Imaging: CT scan shows masses with increased attenuation and enhancement after contrast administration. On MRI:

• T1: hyperintense due to previous haemorrhages and melanin content. After gadolinium administration they show enhancement
• T2: hypointense
• SWI/T2*: susceptibility artefacts due to previous haemorrhages

2.3 Optic nerve glioma

They are rare tumours that usually affect children with neurofibromatosis type 1. They are even rarer in adults, in whom they are not related to neurofibromatosis and are more aggressive. [7]

Fig 6: 43-year-old woman with neurofibromatosis type 1, under follow-up for glioma of the right ocular nerve. The image shows a concentric thickening of the nerve, with enhancement after contrast administration and a subcutaneous neurofibroma.

On imaging they appear as a thickening of the optic nerve (fusiform or exophytic). MRI imaging shows:

• T1: iso/hypointense with respect to the contralateral, with variable enhancement after contrast administration
• T2: show central hyperintensity with a thin peripheral hypointense layer (dura mater)

2.4 Orbital meningioma

Orbital meningiomas can be:

• Primary, rare, most of these are optic nerve sheath meningiomas (≈20%)
• Secondary, the most frequent, caused by extension of an intracranial meningioma into the orbit

They are usually diagnosed in women in the fourth decade of life, although up to 25% are diagnosed in childhood, and these tend towards more aggressive behaviour. In imaging, they behave similarly to intracranial ones, with two characteristic signs being the tram-track and the doughnut, observed in sagittal and coronal reconstructions, respectively. [8]

Fig 7: A 39-year-old male presented to the emergency room for headache, and a CT scan (not shown) showed asymmetry of the cavernous sinus. The MRI study showed occupation of the right cavernous sinus by an ill-defined mass that insinuated towards the orbit, later diagnosed as a meningioma.

2.5 Other metastases

They are rare, with the uveal ones being more frequent than the extraocular ones. The most frequent primary cancers are breast and lung cancer. Their appearance is variable on imaging.

Fig 8: A 66-year-old patient was referred for magnetic resonance imaging for an ocular tumour. The MRI study found a tumour in the posterior pole of the right eyeball with retinal detachment (arrowhead), as well as two cerebellar lesions with enhancement (circle), suggestive of metastatic aetiology. Body imaging subsequently showed the existence of a left apical lung mass (arrow).

3. Inflamatory / Infectious:

3.1 Tolosa-Hunt Syndrome

Tolosa-Hunt Syndrome is defined as an idiopathic granulomatous inflammation of the cavernous sinus or superior orbital fissure. Clinically, it presents as painful paralysis of the third cranial nerve (although it can affect any nerve in the cavernous sinus). Peak incidence is around 40 years of age. [9]

Fig 9: 11-year-old boy with ocular pain and inflammation of two days of evolution with normal ophthalmological examination. The MRI showed ill-defined tissue occupying the posterolateral portion of the right orbit, the superior orbital fissure and the pterygopalatine fossa (arrowhead), as well as inflammatory changes in the extraocular muscles (arrows) and thickening and enhancement of the V1, V2 and V3 branches of the right trigeminal nerve (not shown), suggestive of Tolosa-Hunt syndrome.

CT scan shows asymmetry of the cavernous sinus which may show enhancement. On MRI:

• T1: iso/hyperintense with respect to the muscles. May show gadolinium uptake in the acute phase
• T2: hyperintense

3.2 Dacryocystitis

Dacryocystitis is inflammation of the nasolacrimal sac, due to obstruction of its drainage with secondary infection. It shows two peaks of incidence, in neonates with congenital defects and in the fourth decade of life. Imaging allows us to rule out complications such as abscesses or orbital cellulitis. CT shows fat striation in the inner canthus +/- enhancement. [10]

Fig 10: A 54-year-old patient attended the emergency department for pain and swelling in the right infraorbital region. CT scan showed hyperdensity and effacement of the right nasolacrimal duct (arrow), as well as extension towards the preseptal orbital fat and the anterior third of the ipsilateral postseptal orbital fat (circle), compatible with dacryocystitis.

3.3 Preseptal and postseptal cellulitis

Preseptal and postseptal cellulitis are two diseases that must be differentiated. Their difference lies in whether the involvement is superficial or deep to the orbital septum.

Fig 11: Representation of the basic anatomy of the orbital septum distinguishing between preseptal and postseptal cellulitis.

Fig 12: 10-year-old patient with fever for four days with oedema and erythema of the left lower eyelid, as well as pain with eye movement. CT scan shows preseptal fat stranding compatible with preseptal cellulitis.

Fig 13: A 65-year-old woman presented with periorbital cellulitis on examination with altered level of consciousness, so a CT scan was performed. A subcutaneous abscess and striation of the postseptal fat in the left orbit were observed, as well as ipsilateral frontal subdural empyema.

3.4 Optic Neuritis

Its aetiology is divided into infectious and non-infectious, the latter being the most frequent. It generally affects people around 35 years of age, being more frequent in women.

Fig 15: 26-year-old woman with left eye pain and acute decrease in visual acuity. MRI shows the left optic nerve hyperintense in T2, with enhancement after contrast administration in T1 (arrow) and FLAIR (arrowhead).

4. Vascular pathology:

4.1 Carotid-cavernous fistula

They are an abnormal communication between the carotid circulation and the cavernous sinus. They can be classified in various ways, the vascular anatomy being the most commonly used, being direct or indirect:

• Direct: direct communication between the internal carotid and cavernous sinus
• Indirect: communication through one of the branches of the carotid circulation (internal or external) and the cavernous sinus

The direct ones are usually post-traumatic, of rapid evolution and in young men, while the indirect ones are usually insidious, secondary to predisposing conditions (Ehlers-Danlos for example) and in post-menopausal women.

Fig 16: Representation of Barrow's classification of carotid-cavernous fistulae.

On CT we can see indirect findings such as proptosis, oedema of the orbital fat, enlargement of the extraocular musculature, as well as swelling of the cavernous sinus and arterial enhancement of the ophthalmic vein and the cavernous sinus. [13]

It is important to suspect this pathology in certain traumas, as it is important to diagnose it because of possible complications.

Fig 17: 67-year-old patient brought to the emergency department for severe trauma. CT scan of the encephalon shows a left occipital fracture with extension to the petrous portion of the ipsilateral temporalis (longitudinal type). CT angiography of the cerebral arteries reveals early repletion of the arterial phase of the left superior ophthalmic vein, as well as several hyperdense foci in the left cavernous sinus (circle), indicative of carotid-cavernous fistula.

4.2 Orbital varicose veins

It is the dilatation of the orbital veins, which can be classified as primary or secondary. Primary varicose veins are idiopathic while secondary varicose veins appear due to an increase in blood flow (due to arteriovenous malformations, carotid-cavernous fistulas, etc.). They are usually asymptomatic, although they may debut in young adults with discomfort, proptosis or intermittent diplopia.In the case of suspicion, a CT scan with Valsalva can be performed with contrast administration, with the consequent dilation and enhancement of the pathologic vein. [14]

Fig 18: 94-year-old woman undergoing CT scan for traumatic brain injury. The CT scan showed a superoexternal orbital mass, suggestive of orbital varix.

5. Miscellaneous:

5.1 Posterior dislocation of intraocular lens

It is a rare complication of cataract surgery. They are usually atraumatic (unlike ectopia lentis) within the first 3 months after surgery. May present as vision loss and may be complicated by retinal detachment. [15]

Fig 19: CT images show a posterior dislocation of a correctly positioned intraocular lens in 2021.

5.2 Myopia magna, coloboma and staphyloma

They are different forms of eye enlargement, which differ in some details (see figure 20). [16]

Fig 20: The image shows the characteristic findings of myopia magna, chorioretinal coloboma and staphyloma.

5.3 Intra-ocular silicone oil

Used as a substitute for vitreous humour in some retinal detachment operations, it may simulate vitreous haemorrhage by imaging. [17]

Fig 21: The CT images show hyperdense content in the eyeball, which could be mistaken for vitreous haemorrhage but is intraocular silicone after vitrectomy with ocular cerclage (arrowhead).