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The Orbit


The Orbit

Definition

Disease processes can be classified according to the anatomical site involved – this is usually in relation to the rectus muscle pyramid (the ‘cone’)

Intraconal (within the muscle cone)

  • Optic nerve glioma

  • Optic nerve meningioma

  • Haemangioma

  • Inflammatory orbital pseudotumour

  • Lymphoma ▸ metastases

Arising from the muscle cone

  • Inflammatory orbital pseudotumour

  • Dysthyroid ophthalmopathy

  • Rhabdomyosarcoma (the commonest cause of a paediatric primary orbital mass)

Extraconal (outside the muscle cone)

  • Orbital cellulitis or abscess

  • Lymphoma ▸ metastases

  • Dermoid ▸ epidermoid ▸ teratoma

  • Lymphangioma ▸ lymphohaemangioma

Within or involving the globe

  • Retinoblastoma

  • Melanoma

  • Metastases

The imaging findings of some less common diseases of the conal and intraconal compartments *
Pathology Clinical features Key imaging findings
Congenital Optic nerve hypoplasia

  • Can be isolated or part of a syndrome (e.g. septo-optic dysplasia)

  • Decreased size of the optic nerve

Inflammatory Optic neuritis

  • About 50% of patients with idiopathic optic neuritis develop multiple sclerosis

  • Other causes include sarcoid, radiation, pseudotumour, toxoplasmosis, TB, syphilis, virus infection

  • Best seen on gadolinium-enhanced T1W imaging

  • If present, look for brain demyelination using T2W imaging

Tumour Leukaemia

  • Reported in 13–16% of cases of leukaemia

  • More commonly an acute lymphoblastic leukaemia but described in AML and adult leukaemias

  • Presents with papilloedema and variable loss of acuity

  • Diffuse enlargement of the optic nerve with variable enhancement

Haemangioblastoma

  • Associated with von Hippel–Lindau (VHL) disease

  • Progressive loss of vision

  • Retinal lesions occur in 60% of patients with VHL

  • Rarely affects the orbit or optic nerve

  • Sharply demarcated from the nerve

  • Densely enhancing

  • Usually affects the prechiasmatic nerve

Haemangiopericytoma

  • Mean age 40–60 years

  • More common in women

  • Presents with proptosis, optic nerve and extraocular dysfunction

  • Superior orbital masses

  • Tends to invade locally

  • Marked contrast enhancement

  • Florid blush on angiography

Neurofibroma/ schwannoma

  • About 1% of orbital tumours

  • Affects young adults

  • Usually presents with proptosis

  • Neurofibromatosis in 2–18%

  • Smooth, ovoid, solitary mass

  • Usually in the superior orbit

  • May be intraconal, extraconal or intramuscular

  • Isodense with homogeneous contrast medium enhancement on CT

  • Isointense on T1 and hyperintense on T2WI

Miscellaneous Raised intracranial pressure

  • Papilloedema, loss of venous pulsation

  • Dilatation of the optic nerve sheath

The imaging findings of some less common diseases of the globe *
Pathology Clinical features Key imaging findings
Congenital PHPV (persistent hyperplastic primary vitreous)

  • The primary vitreous normally involutes by the 6 th fetal month, but occasionally persists and undergoes hyperplasia

  • Presents with leucocoria

  • Affects male infants more than female

  • Secondary retinal detachment is common (a V-shaped structure within the globe on axial imaging)

  • A microphthalmic globe with enhancing and increased density in the vitreous humour on CT

  • A soft tissue cone or band from the back of the lens to the posterior globe

  • Can be unilateral or bilateral

Retinopathy of prematurity

  • A history of prolonged ventilation with high O 2 concentration in a premature baby

  • Pathology shows abnormal and disorganized proliferation of retinal vascular buds ▸ may cause retinal detachment

  • Bilateral increased density in the vitreous

  • Calcification is rare

Coat's disease

  • A congenital vascular malformation of the retina with telangiectasia ▸ usually unilateral ▸ presents in childhood

  • Exudation from abnormal vessels leads to retinal detachment ▸ disease nature if progressive

  • Increased density in all or part of the vitreous

  • Normal-sized globe

  • No calcification

Microphthalmia

  • Congenital underdevelopment or acquired diminution in size of the globe

  • Associated with congenital rubella, PHPV, retinopathy of prematurity and Lowe syndrome

  • Congenital = small globe in a small orbit

  • Acquired = small, calcified globe

Macrophthalmia

  • Enlargement of the globe

  • The most severe form is called buphthalmos

  • Associated with juvenile glaucoma

  • A large globe in a large orbit

  • Also seen in Marfan's/Ehlers–Danlos syndrome

Coloboma

  • A defect in the globe, usually near the optic nerve head

  • It involves the sclera, uvea and retina

  • It is caused by a defect in fetal optic fissure

  • A small globe with cystic outpouching of the vitreous

  • There may be a retro-ocular cyst

Degenerative Drusen

  • Accretion of hyaline material on the optic disc

  • It may be asymptomatic or associated with headache or visual field defects

  • Discrete, flat calcification of the optic nerve head

  • Bilateral in 75%

Phthisis bulbi

  • An end-stage injured eye

  • A collapsed globe

  • It may be calcified

Inflammatory Scleritis

  • Anterior scleritis presents with pain, erythema, photophobia and tenderness

  • Posterior scleritis is painless and may mimic melanoma

  • Thickened enhancing sclera

  • Choroidal detachment may be present

Sclerosing endophthalmitis

  • A 2–8-year-old child exposed to soil contaminated by dog faeces

  • Ingestion of the ova of Toxocara canis results in ophthalmitis

  • Dense vitreous without a discrete mass

  • No calcification

Tumour Choroidal haemangioma

  • Can be isolated or associated with Sturge–Weber syndrome

  • A benign vascular lesion

  • Lenticular or flat densely enhancing eye wall mass

Medulloepithelioma

  • Mean age of onset 4 years

  • It presents with a ciliary body mass, lens coloboma, lens subluxation, cataract, cyclitic membrane and glaucoma

  • About 50% are teratoid and 50% non-teratoid

  • Involvement of the ciliary body helps differentiate from a retinoblastoma

  • Only 10–15% are calcified

  • It rarely may involve the optic nerve and other locations in the CNS

The imaging findings of some less common diseases of the extraconal compartment *
Pathology Clinical features Key imaging findings
Congenital Cephalocele

  • Present soon after birth

  • A soft mass near the medial canthus

  • It may be pulsatile and increased with Valsalva

  • Soft tissue and CSF continuous with the intracranial contents

Dermoid

  • Usually the upper outer quadrant of the orbit

  • A fullness or small lump

  • Usually anterior between the globe and periosteum

  • A well-defined cystic mass

  • Epidermoid – fluid density, dermoid – fat density on CT

  • May be related to sutures

Lacrimal gland inflammatory Postviral

  • The commonest cause of acute inflammatory enlargement in younger patients

  • Smooth enlargement of the gland

Sjögren's syndrome

  • Decreased lacrimation and dry mouth

  • May be primary or secondary to autoimmune connective tissue diseases

  • Histology = lymphocytic infiltration of the gland

  • Non-specific enlargement of the gland in the acute phase

  • The gland may be small in chronic phase

  • Enhancement is patchy or absent

Mikulicz disease/ syndrome

  • Mikulicz disease is similar to primary Sjögren's syndrome

  • Mikulicz syndrome is gland enlargement associated with sarcoid, lymphoma, leukaemia or TB

  • As for Sjögren's syndrome

Tumour Benign mixed tumour

  • Same as a pleomorphic adenoma

  • Benign

  • Represents about 50% of primary lacrimal gland neoplasms (the rest are malignant)

  • It can undergo malignant change

  • Well-defined, smooth enlargement of gland

  • Long-standing so there may be bone remodelling

  • May not enhance

Adenoid cystic carcinoma

  • The most common malignant primary tumour (followed by malignant mixed tumour, adenocarcinoma and mucoepidermoid carcinoma)

  • Tumour is hard enough to indent the globe

  • The gland may have a serrated edge

  • A tendency for perineural spread

  • Enhances well

Lymphoma (NHL)

  • The lacrimal gland is a common site for NHL in the orbit

  • Infiltrating mass

  • Enhances well

Congenital microphthalmos. Axial CT image. There is choroidal calcification (large black arrow) with a small globe, a thinned optic nerve (small white arrows) and a small orbit. Note the hypoplastic optic canal (black arrowhead). *

Drusen. Axial CT. There are small foci of calcification at both optic nerve heads. *

Phthisis bulbi. Axial CT. The patient had been stabbed in the right eye 2 years previously. The globe is small and densely calcified. *

Optic neuritis. Coronal T2WI with inversion recovery. There is high signal in the left optic nerve, indicating optic neuritis. The patient was symptomatic and had multiple demyelinating lesions in the cerebral white matter. *

Coloboma. Axial CT image demonstrates bilateral retinal defects with outpouching in the region of the optic nerve head. †

Persistent hypertrophic primary vitreous. Axial CT of the orbits demonstrates a small left globe with a V-shaped retrolental density (A). **

Conal and Extraconal Disorders

Conal Compartment – Thyroid Ophthalmopathy

Definition

This results from deposits of hygroscopic mucopolysaccharides and infiltration of the lymphocytes, mast and plasma cells

  • It is the commonest cause of an adult unilateral or bilateral exophthalmos

  • 85% are bilateral (but are often asymmetrical)

Clinical presentation

An insidious and painless exophthalmos (± lid lag) ▸ only 10% of patients are euthyroid ▸ 4th–5th decade ▸ F : M – 4 : 1

Radiological features

CT/MRI

An increased intraorbital fat volume – especially within the anteromedial extraconal space (fat hypertrophy may also be seen with steroid therapy and Cushing's disease) ▸ fusiform enlargement and enhancement of the extraocular muscle bellies (with sparing of the tendinous insertions) ▸ the hypertrophied muscles and increased fat content may lead to crowding of the orbital apex (with possible optic nerve compression and decreased vision)

  • All of the intraocular muscles are usually involved ▸ if there is isolated enlargement of the lateral rectus muscle belly, then causes other than a thyroid ophthalmopathy should be sought (e.g. a pseudotumour)

    • ▪

      The order of muscular involvement: i nferior rectus ▸ m edial rectus ▸ s uperior rectus ▸ l ateral rectus ▸ the o blique muscles (‘ I'M SLO W’)

  • With advanced disease the lamina papyracea may demonstrate a concavity due to the raised intraorbital pressure

  • Dynamic contrast-enhanced MRI : the mean of peak enhancement ratio values for the extraocular muscles in Graves' disease tends to decrease according to the severity of the clinical and anatomical changes ▸ the mean rate of enhancement also decreases according to the disease severity

Conal Compartment – Rhabdomyosarcoma

Definition

A highly malignant primary orbital tumour originating from the extraocular muscles, nasopharynx and paranasal sinuses (this is the most common site for a head and neck rhabdomyosarcoma)

Clinical presentation

It is seen in children aged 2–5 years and presents with a rapidly progressive exopthalmos ▸ metastases are typically haematogeneous (lung/bone the most common)

Radiological features

CT

A bulky aggressive-looking isodense or slightly hyperdense mass usually located within the superomedial orbit ▸ it demonstrates uniform enhancement and is associated with bone destruction ▸ no calcification

MRI

T1WI/T2WI: intermediate SI

Extraconal Compartment – Retrobulbar Metastases

Definition

Most retrobulbar metastases are extraconal in location and subsequently encroach on the intraconal compartment as they increase in size ▸ they usually produce an infiltrating poorly marginated mass ▸ they usually originate from the greater sphenoid wing with associated bone destruction

  • Adults: an infiltrative retrobulbar mass (+ enophthalmos) is characteristic of a scirrhous carcinoma of the breast

  • Children: smooth extraconal masses related to the posterior lateral orbital wall is seen with metastases from a neuroblastoma or Ewing's sarcoma

Radiological features

CT

An infiltrating poorly marginated mass which is isodense or hyperdense ▸ there is enhancement following IV contrast medium administration

  • Their baseline hyperdensity and lack of invasion of the preseptal compartment differentiates them from a rhabdomyosarcoma

Extraconal Compartment – Dermoid/Epidermoid

Definition

A cystic lesion resulting from a congenital epithelial inclusion ▸ it is classified as a true choristoma (i.e. a tumour composed of tissue not normally found at the site of occurrence) ▸ it is the commonest periorbital mass lesion found in infants and children

  • Dermoid: composed of epithelial and dermal elements

  • Epidermoid: composed of epithelial elements only

Radiological features

CT

An ovoid, well-demarcated cystic mass lesion ▸ there may be fat (50%) or calcification (15%) present ▸ there can be bone remodelling and rim enhancement ▸ the lesion may rupture

  • The majority are found within an extraconal location, occupying the superolateral aspect of the anterior orbit (and related to the frontozygomatic suture)

MRI

T1WI: high SI (if fatty) or intermediate SI ▸ T2WI: low-to-intermediate SI ▸ T1WI + Gad: thin rim enhancement unless rupture has occurred

Dermoid. (A) Axial and (B) coronal CECT. There is a fat density mass in the superolateral left orbit with a thick enhancing capsule (arrows). Subtle deformity of the adjacent bone is noted. *

Differentiation between a pseudotumour and thyroid ophthalmopathy
Pseudotumour Thyroid ophthalmopathy
Involvement Usually unilateral Usually bilateral
Tendon involvement Yes No
Orbital fat Hyperdense (inflammation) Increased amounts
Effect of steroids Marked Minor

Thyroid ophthalmopathy. (A) Axial and (B) coronal CT imaging. There is generalized enlargement of the bellies of all the extraocular muscles, proptosis and increased intraorbital fat. *

Rhabdomyosarcoma. (A) Axial and (B) coronal CECT. There is a large uniformly enhancing mass in the superior right orbit which is difficult to separate from the extraocular muscles. *

Breast metastasis to the left orbit. (A) Breast carcinoma with enophthalmos of the left globe secondary to the tumour desmoplastic reaction. (B) T1WI + Gad FS: there is subarachnoid seeding along the optic nerve (arrowheads) and in the posterior midbrain (open arrow). Also note the large mass in the right temporal region (arrow). +

Intraconal Disorders

Idiopathic Orbital Pseudotumour

Definition

  • An autoimmune idiopathic inflammatory condition affecting the orbital soft tissues ▸ it is the commonest cause of an adult intraorbital mass

  • Affects any age ▸ M=F

  • Any orbital structure can be affected, in the following order of frequency: the retrobulbar fat ▸ the extraocular muscles ▸ lacrimal gland ▸ the optic nerve ▸ the globe (the uveal-scleral area)

    • ▪

      Tumefactive type: there is diffuse involvement of the conal and intraconal structures

    • ▪

      Myositic type: this involves the extraocular muscles

    • ▪

      Tolosa–Hunt syndrome: an idiopathic inflammatory condition similar to a pseudotumour and affecting the cavernous sinus and orbital apex (it can also present with a painful ophthalmoplegia)

Clinical Presentation

  • There is a rapid onset in middle age with a unilateral painful ophthalmoplegia, proptosis and chemosis

    • ▪

      Acute: there is a rapid and lasting response to steroids ▸ this is the more common presentation

    • ▪

      Chronic: there is a poor response to steroids with subsequent fibrosis (requiring chemotherapy and radiotherapy)

Radiological Features

CT

‘Dirty fat’: subtle hyperdensity of the intraorbital fat ▸ there is enhancement of the affected regions following the administration of IV contrast medium

MRI

T2WI: low SI (true tumours generate high SI)

Pearls

  • 10% are associated with other systemic autoimmune conditions: Wegener's granulomatosis ▸ fibrosing mediastinitis ▸ Riedel's thyroiditis ▸ sclerosing cholangitis ▸ retroperitoneal fibrosis ▸ polyarteritis nodosa ▸ dermatomyositis ▸ rheumatoid arthritis

  • Involvement of a unilateral single extraocular muscle ( including the tendinous insertion ) is highly suggestive of a pseudotumour rather than thyroid ophthalmopathy ▸ the tendon is spared in thyroid disease ▸ frequency of muscular involvement: medial rectus > superior rectus > lateral rectus > inferior rectus

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