Thyroid-Associated Orbitopathy

Thyroid associated orbitopathy (TAO) has gone by a number of other terms, including thyroid eye disease, thyroid ophthalmopathy, Graves disease and endocrine ophthalmopathy. It is characterised by enlargement of the extraocular muscles (EOMs) as well as increase in the retroorbital fat. The muscles are infiltrated with inflammatory cells (lymphocytes, macrophages, plasma cells and eosinophils), have increased mucopolysaccharide deposition, and enlarged fibroblasts and increased collagen deposition.
This results in:
proptosis, with resultant chemosis and corneal dryness and damage;
optic nerve compression;
diplopia;
The order of extraoccular muscle involvement can be remembered by the mnemonic I’M SLOW, and bilateral (90%) and symmetric (70%) involvement is typical. The tendon is typically spared (although it can be involved in acute cases) with the swelling largely confined to the muscle belly. This helps to distinguish TAO from many of the differentials, along with their even distribution among the EOMs and more frequent unilateral or asymmetric involvement. It may precede, occur concurrently with, or after onset of abnormal thyroid function.
For more images of the same case and more about TAO please visit Radiopaedia.org here.
References:
1. eMedicine
2. Harnsberger R, et al. Diagnostic imaging: Head and Neck Amirsys
Credit: Dr Frank Gaillard
http://www.radpod.org