Quantitative Analysis of Inflammation in Orbital Fat of Thyroid-associated Ophthalmopathy Using MRI Signal Intensity

We quantitatively analyzed inflammation in orbital fat from cases of thyroid-associated ophthalmopathy (TAO) using short-tau inversion recovery (STIR) sequences from magnetic resonance imaging. The signal intensity ratios (SIRs) of orbital fat as well as the superior rectus (SR), inferior rectus (IR), lateral rectus (LR), medial rectus (MR), and superior oblique (SO) muscles on STIR images were measured in 70 eyes from 70 treatment-naive TAO patients (active TAO group, 19 patients; inactive TAO group, 51 patients) and 20 eyes from 20 controls. The mean SIR in the active TAO group was significantly higher than that in the inactive TAO group and controls (P < 0.001). The SIR of orbital fat in all TAO patients was significantly (P < 0.001) positively correlated with that of the extraocular muscles: SR (r = 0.64), IR (r = 0.55), LR (r = 0.58), MR (r = 0.71), and SO (r = 0.65). The SIR of orbital fat had a significant positive correlation with the CAS (r = 0.53, P < 0.001). The measurements of SIRs in orbital fat may be useful in evaluating the activity in tissues of TAO patients.