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Thyroid Ophthalmopathy


KEY FACTS

Terminology

  • Synonyms: Graves ophthalmopathy, thyroid orbitopathy

  • Autoimmune orbital inflammatory condition associated with thyroid dysfunction

Imaging

  • CT

    • For uncomplicated disease and surgical planning

    • Nonuniform, symmetric, or asymmetric extraocular muscle involvement

    • Enlargement of muscle bellies, sparing tendinous insertions

    • “I'M SLO” mnemonic for sites of predilection

      • –

        I nferior > m edial > s uperior > l ateral > o blique

    • Increased volume of orbital fat

      • –

        Caution: Extraocular muscles may look normal

  • MR

    • Assess disease activity

    • ↑ T2WI MR signal acutely due to edema

    • ↓ T2WI MR signal chronically due to fibrosis

  • US: Effective for bedside diagnosis

Top Differential Diagnoses

  • Idiopathic orbital inflammatory pseudotumor

  • Sarcoidosis

  • Lymphoproliferative lesions

Pathology

  • Autoantibodies target thyrotropin receptors found in both thyroid gland and orbit

  • Cellular infiltrate with hyaluron deposition acutely

  • Fibrosis and muscle degeneration in chronic phase

Clinical Issues

  • Typical patient is middle-aged woman with periorbital edema, proptosis, and restricted gaze

  • Corticosteroids 1st line of therapy in acute disease

  • Surgery for decompression in severe cases

Coronal graphic shows bilateral symmetric enlargement of extraocular muscles
. Irregularity within the muscles
represents accumulation of lymphocytes and mucopolysaccharide deposition.

Clinical photograph of a patient with severe thyroid ophthalmopathy shows bilateral proptosis
, lid retraction
, and disconjugate gaze
.

Coronal NECT shows enlargement of the bilateral inferior, medial, and superior rectus muscles
in a patient with thyroid ophthalmopathy. Mucopolysaccharide deposition manifests as areas of low density
within the muscles, particularly inferior recti.

Axial NECT in another case with thyroid ophthalmopathy demonstrates proptosis (globes displaced anteriorly beyond the lateral orbital walls/dotted line), fusiform enlargement of medial
and lateral
recti with striking sparing of tendon sheaths
.

TERMINOLOGY

Synonyms

  • Graves ophthalmopathy, thyroid orbitopathy

Definitions

  • Autoimmune orbital inflammatory condition associated with thyroid dysfunction

IMAGING

General Features

  • Best diagnostic clue

    • Exophthalmos and bilateral extraocular muscle (EOM) enlargement

  • Location

    • Nonuniform, symmetric EOM involvement

      • –

        Bilateral in 90%; symmetrical in 70%

        • □

          Even if symptoms are unilateral

      • –

        I'M SLO mnemonic for sites of predilection

        • □

          Inferior ≥ medial ≥ superior > lateral ≥ oblique

        • □

          Superior recti frequent in some reports

        • □

          Lateral recti and obliques least likely

      • –

        Isolated muscle involvement in 5%

        • □

          Particularly superior recti

  • Size

    • EOM enlargement varies with disease severity

    • Normative EOM thickness (mm) at mid-belly based on CT data

      • –

        Inferior: 4.8, medial: 4.2, superior: 4.6, lateral: 3.3

      • –

        Thickness > 5 mm considered abnormal

  • Morphology

    • Enlargement of muscle bellies ; typically spares tendons, but may be involved in acute phase

CT Findings

  • NECT

    • Isodense enlargement of EOM

      • –

        Heterogeneous areas of internal lower density, indicating glycosaminoglycan deposition

    • Exophthalmos

      • –

        Line drawn between lateral orbital rims demonstrates degree of exophthalmos

    • Other features

      • –

        Increased orbital fat , especially in patients < 40 years

      • –

        Straightened (“stretched”) optic nerve

      • –

        Lacrimal gland enlargement

  • CECT

    • Superior ophthalmic vein enlargement

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