Orbital disease

Lesion

Anything that fills the orbit pushes the eye forward: swollen muscles in Graves disease, inflammation, infection or a tumour.

Updated Nov 12, 2026

Key points

Thyroid-associated orbitopathy: TSH-receptor antibodies activate orbital fibroblasts; glycosaminoglycans and lymphocytes swell the muscles, sparing the tendons; lid retraction and proptosis.
Most common cause of proptosis in adults, on one or both sides; can compress the optic nerve at the orbital apex.
Idiopathic orbital inflammation (orbital pseudotumour): painful mixed inflammation and fibrosis without a cause; IgG4-related disease is a separate fibroinflammatory cause.
Orbital lymphoma is usually extranodal marginal zone (MALT) lymphoma, sometimes with lacrimal gland involvement.
Lacrimal gland: pleomorphic adenoma (benign) and adenoid cystic carcinoma (perineural spread, painful).
Children: capillary hemangioma (infantile), dermoid cyst, rhabdomyosarcoma (embryonal type, rapid proptosis).

What it is

The orbit is a bony cone with fixed volume, so swelling of its contents pushes the globe forward (proptosis) and can compress the optic nerve. The commonest cause in adults is thyroid-associated orbitopathy, in which autoimmune inflammation enlarges the extraocular muscles and orbital fat. Other inflammations include idiopathic orbital inflammation, IgG4-related disease, sarcoidosis and granulomatosis with polyangiitis; orbital cellulitis spreads from the sinuses. Tumours include lymphoma, lacrimal gland neoplasms, vascular lesions and, in children, rhabdomyosarcoma.

Step by step

Antibodies against the TSH receptor reach orbital fibroblasts, which also express it.
Fibroblasts and T cells release cytokines; fibroblasts make hydrophilic glycosaminoglycans.
Glycosaminoglycans bind water; muscles and fat swell.
The globe is pushed forward and the eyelids retract.
Crowding at the apex can compress the optic nerve; late fibrosis limits eye movements.

Causes of proptosis

Cause	Typical patient	Pathology
Thyroid-associated orbitopathy	Adult with Graves disease	Swollen muscle bellies with glycosaminoglycans, lymphocytes, later fibrosis
Orbital cellulitis	Child with sinusitis	Acute bacterial inflammation behind the septum
Idiopathic orbital inflammation	Adult, painful onset	Mixed inflammation and fibrosis
IgG4-related disease	Older adult, lacrimal swelling	IgG4 plasma cells, storiform fibrosis, obliterative phlebitis
Granulomatosis with polyangiitis	Adult with sinus and kidney disease	Necrotising granulomatous vasculitis
Orbital lymphoma	Older adult, painless	Monoclonal B cells, often MALT type
Cavernous venous malformation	Middle-aged adult	Encapsulated dilated vascular channels
Rhabdomyosarcoma	Child, rapid onset	Small round cells with skeletal muscle markers

Clinical notes

Smoking worsens thyroid-associated orbitopathy and should be stopped.
Exposure of the cornea and compressive optic neuropathy are the threats to sight.

Test yourself

Think of the answer, then tap the question to see it.

Which part of the extraocular muscles is enlarged in thyroid-associated orbitopathy?

The muscle bellies, with the tendons spared, from glycosaminoglycan deposition and inflammation.

What is the most common type of lymphoma in the orbit?

Extranodal marginal zone (MALT) lymphoma.

Which malignant orbital tumour causes rapid proptosis in a child?

Rhabdomyosarcoma, usually the embryonal type.

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Connections

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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: Graves Disease (StatPearls (NCBI Bookshelf), 2026); Orbital Cellulitis (StatPearls (NCBI Bookshelf), 2026).

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Representative model, for educational purposes only.