1 – Endocrine orbitopathy 

Autoimmune inflammatory orbital condition associated with thyroid dysfunction. It is the most common cause of exophthalmos in adults, often self-limited and with a good prognosis. Affect patients of both sexes in any age group, but is more common in women between the ages of thirty and fifty.

Inflammation compromises the extrinsic muscles, lacrimal gland, intraorbital fat and connective tissue, with increase in volume. In the later stages, fibrosis and muscle degeneration occur, with exophthalmos reduction.

Both CT and MRI demonstrate the macroscopic changes and allow the exclusion of other etiologies, but MRI is the first choice. The most characteristic finding is fusiform volume increase of the extrinsic muscles, with involvement of the muscle bellies, sparing the tendons. In the acute phase, there is intense enhancement of the muscles and conjunctiva (Fig 3).

The frequency of muscle involvement is in descending order: inferior rectus, medial rectus, superior rectus, lateral rectus and superior oblique.

2 – Orbital lymphomas 

They represent around 10% of orbital tumors, encompass a variable spectrum from lymphoid hyperplasia to lymphoma, and are more common in women over sixty years of age.

They can occur anywhere in the orbit, but are more common in the conjunctiva and lacrimal gland. 

In the rest of the orbit the presentation is very variable. There may be a solid mass that molds to or surrounds the orbital structures. Less frequently, it diffusely infiltrates the orbital fat with multicompartment involvement. Other findings are proptosis, diplopia, fever, night sweats and weight loss.

When the lesion appears as a tumor, it adapts to neighboring structures and tends to be anterior. At CT, they present intermediate density compared to muscle, and on MRI, T1-intermediate signal intensity.

On T2-weighted images there is a tendency towards hypointensity, as it is a hypercellular lesion (however, there may also be T2 high signal). There is usually diffusion restriction as well.

There is moderate/marked and homogeneous contrast enhancement on MRI and CT. This pattern of intermediate T1 signal intensity, T2 hypointensity, diffusion restriction and contrast enhancement also tends to be observed when there is glandular, muscular or diffuse involvement (Fig 4).

3 – Optic glioma 

It is the most common primary tumor of the optic nerve. In half of the cases it is restricted to the intraorbital portion of the optic nerve. Around 60% manifests itself in children under 8 years of age, rarely occurring in adults, when it is almost always malignant. They are associated with type 1 neurofibromatosis in up to 40% of cases. It may be asymptomatic or present with reduced visual acuity, relative afferent pupillary dysfunction, proptosis or strabismus.

MRI is the imaging method of choice. Lesions are typically isointense on T1-weighted sequences and isointense to hyperintense on T2-weighted sequences. Contrast agent uptake is variable. Cystic spaces or necrosis may be seen in the lesion. It is generally not possible to distinguish the nerve itself from the glioma, and this feature is very useful in the differential diagnosis with meningioma (Fig 5).

4 – Capillary hemangioma 

It is the most common orbital vascular tumor in childhood. They appear soon after birth, grow quickly and then gradually regress. More common in girls, in a ratio of 3:2. The majority are located in the extraconal compartment.

They are not encapsulated and consist of multiple lobes separated by fibrous septa. There may be involvement of the extrinsic muscles and the lacrimal gland.

The lesion is noticed on average in the second week after birth, with the majority appearing in the first three months. The most common symptoms arise from a growing soft tissue mass, typically with redness and heat or skin discoloration. Involution occurs spontaneously in the following years, in most cases until 9-10 years of age. They can occur alone or in association with several syndromes, such as PHACE syndrome.

CT is the modality of choice as sedation is not required. Capillary hemangiomas are usually lobulated and heterogeneous, are not encapsulated, have irregular margins, and demonstrate intense contrast enhancement. On MRI, they are usually T1-hypointense, T2-isointense to hyperintense. Lobules with thin septa inside combined with perilesional flow voids are characteristic (Fig 6). The most important data for diagnosis is that the lesion appears after birth and that there are no febloliths.

5 – Orbital and periorbital cellulitis and abscesses 

They can be pre-septal or post-septal. Pre-septal cellulitis is most often caused by trauma or insect bites, particularly in children. Intraorbital cellulitis is most often caused by sinusitis.

The most common clinical presentation of pre-septal cellulitis is periorbital edema and erythema, which is easy to diagnose clinically. Post-septal cellulitis manifests with anterior displacement of the eyeball and ophthalmoplegia, accompanied by fever, pain, bruising and malaise. It can progress to intraorbital or periorbital abscess formation.

The most typical finding is periorbital or intraorbital infiltration with mass effect and contrast enhancement. There may be indefinition of the orbital planes, intraconal or extraconal soft tissue mass, edema of the extrinsic muscles and/or abscess formation. Both CT and MRI show orbital and periorbital infiltration with diffuse and heterogeneous enhancement. On MRI, there is hypointense infiltration of the orbital fat on T1-weighted images, hyperintense on T2-weighted images, and heterogeneous enhancement (Fig 7).

6 – Osteoid osteoma 

Osteoid osteomas are benign bone tumors, usually located within the cortex of long bones in the lower extremities. They are well-demarcated lesions with an osteoblastic nidus and a distinct surrounding zone of reactive bone sclerosis, rarely exceeding 1 cm in diameter. They are rare in the skull area, representing less than 1% of cases.

Radiologically it is composed of a translucent central area surrounded by a larger area of dense reactive bone (Fig 8).

Among bony orbital tumors, fibrous dysplasias and osteomas are the most commonly encountered entities, often originating from the paranasal sinuses. Osteomas are slow growing lesions that do not metastasize.

They are often completely asymptomatic, unless they arise in an area that compromises vision or hearing, like the orbits.

7 – Choroidal detachment 

Choroidal detachment is defined as fluid accumulation in the subchoroidal space, a condition that may occur after ocular surgery, trauma, or an inflammatory choroidal process (uveitis). Choroidal detachment spares the region of the optic disc, in the posterior third of the globe, because of the anchoring effect of short posterior ciliary arteries, veins, and nerves in the ciliary body. The sparing of this region gives choroidal detachment its characteristic imaging appearance (Fig 9).

The possible presence of an underlying ocular mass (eg, retinoblastoma in children, uveal melanoma or choroidal metastases in adults) should be considered when a retinal or choroidal detachment is detected.

8 – Orbital cryptococcosis 

Cryptococcus spp. is a common fungal infection and frequent cause of meningitis in immunocompromised patients; however, immunocompetent patients are also at risk of infection. Visual loss often occurs via elevated intracranial hypertension but can rarely occur through direct optic nerve, chiasm, or tract invasion.

Magnetic resonance of imaging (MRI) of the brain and orbits can show multiple areas of ill-defined enhancement in the optic nerve sheaths, optic chiasm and tracts in the acute phase and nerve atrophy in late stages (Fig 10).