Thyroid ophthalmopathy : CT

Case Report:40 yr old female known case  of Thyroid disease  with lids pain shows classical  exopthalmos (distance nearly zero) belly enlargement of all extra ocular muscles with compression of superior  opthalmic vein/ optic nerve at apex with increased retro orbital  fat  volume  consistent  with TAO (Thyorid associated opthalmopathy)

Teaching points by Dr MGK Murthy 

1. Exact etiology not known , possibly TSH antibodies   produce inflammatory response of the muscles due to shared antigens , and belly of the muscles show enlargement with  inflammatory exudates, mucopolysaccarides and later collagen leading to fibrosis. 

2. Sequence of  involvement is IMSLOW (inferior/ medial/superior/ lateral/ obliques) with tendons spared 

3. Exopthalmos measured by horizontal line  joining the zygomatic bones tips in  CT axials with post eye balls  distance from this horizontal (Normal 10+/- 1.7mm) 

4.  Optic nerve at orbital apex(depends on the shape of orbit), superior opthalmic veins get compressed  (latter leading to retro orbital fat volume increase) 

5.Surpirisingly self limiting in majority of cases (<5yrs) . bilateral  and symmetrical in 70%

6.Steroids/ other/ decompression  may be needed

7. Though common with Graves disease, hashimotos Thyroiditis may  be  associated .

8. Thyroid abnormality  may occur  together, earlier or even later