Extraocular muscle enlargement (EOME) can occur secondary to an array of inflammatory, neoplastic, infective or vascular conditions. Orbital imaging with computed tomography (CT) or magnetic resonance imaging (MRI) plays an essential role in the workup of these conditions. High resolution orbital MRI has allowed for a more detailed characterisation of orbital disease. Recognising the pattern of muscle involvement along with accompanying orbital signs can help with diagnosis. This review focuses on the radiological findings associated with pathology that cause EOME.

A systematic review was conducted across a variety of databases looking at the imaging features of extraocular muscle enlargement. A total of 171 different resources were identified.

Thyroid Eye disease Thyroid eye disease (TED) is the most common cause of EOME. Radiologically, it presents with bilateral enlargement of the muscle belly with relative sparing of the anterior tendon. Traditionally, muscles are said to be involved in the following order: inferior rectus, medial rectus, superior rectus and lateral rectus. However, it is now being recognised that superior muscle complex involvement is also very frequent.[2, 3] Furthermore, isolated levator muscle enlargement can also occur and is associated with upper eyelid retraction.[2-4]. Most patients with...

EOME is most commonly due to thyroid eye disease, however, it can occur secondary to multiple other conditions. Imaging is playing an increasingly important role in the characterization of orbital diseases. Ultimately the diagnosis will be made in conjunction with the patient’s demographics, past medical history and presentation. In cases where there is diagnostic uncertainty, an orbital biopsy may be required for definitive diagnosis.

Enzmann DR, Donaldson SS, Kriss JP (1979) Appearance of Graves' disease on orbital computed tomography. J Comput Assist Tomogr 3: 815-819 Davies MJ, Dolman PJ (2017) Levator Muscle Enlargement in Thyroid Eye Disease-Related Upper Eyelid Retraction. Ophthalmic Plast Reconstr Surg 33: 35-39 https://10.1097/iop.0000000000000633 Wang Y, Mettu P, Broadbent T, Radke P, Firl K, Shepherd JB, 3rd, Couch SM, Nguyen A, Henderson AD, McCulley T, McClelland CM, Mokhtarzadeh A, Lee MS, Garrity JA, Harrison AR (2020) Thyroid eye disease presenting with superior rectus/levator complex enlargement. Orbit...