mercoledì 11 luglio 2007
Figure 1: Axial CT-There is symmetrical proptosis on both sides. There is marked homogeneous enlargement of the muscle bellies of the extraocular muscles.
Figure 2: Coronal CT- Demonstrates enlargement of multiple muscles within the orbits bilaterally, with relative sparing of the lateral recti muscles.
Figure 3: Sagittal CT- There is crowding at the orbital apex with straightening of the optic nerve.
Figure 4: Axial postcontrast MRI – Homogeneous enhancement of the enlarged muscle bellies. There is marked bending of the lamina papyracea secondary to marked enlargement of medial recti muscles on both sides.
Diagnosis: Thyroid associated orbitopathy (Graves ophthalmopathy)
Thyroid associated orbitopathy (TAO), frequently termed Graves ophthalmopathy, is an autoimmune orbital inflammatory condition that is strongly associated with dysthyroidism. The lymphocyte-mediated inflammatory process affects the extraocular muscles, periorbital fat and connective tissues.
The eye findings associated with Graves disease can occur before, during, or long after the thyroid disease has been discovered or treated. While the orbitopathy is most commonly associated with hyperthyroid states, it can be seen in euthyroid and even hypothyroid patients.
It is associated with:
1) Graves hyperthyroidism (80%);
2) Hashimoto's thyroiditis (10% to 15%); or
3) unclassified thyroid immunologic abnormality (5%).
Thyroid associated orbitopathy usually affects young and middle-aged adults, females being affected 3 to 6 times more commonly than males. It may result in eyelid retraction, proptosis, chemosis, periorbital edema, and altered ocular motility with vision-threatening exposure keratopathy, troublesome diplopia, and compressive optic neuropathy occurring in untreated cases. TAO usually has a self-limited course, but significant chronic orbitopathy may occur in 10% to 15% of cases. Stable TAO can occasionally reactivate, but this is uncommon.
Orbital involvement is bilateral in 90% cases, although it may be asymmetric and symptoms may be unilateral. There is bilateral enlargement of extraocular muscles with increased orbital fat resulting in exophthalmos. The inferior and medial recti muscles are first to be involved. The lateral rectus muscle is the last to be involved and rarely shows isolated involvement. Muscle enlargement characteristically involves the belly, sparing the tendinous attachment to the globe.
Lacrimal gland enlargement may be seen. CT and MRI may also show “stretching” and apical crowding of the optic nerve with an enlarged superior ophthalmic vein.
TAO usually has a self limited course with favorable outcome. In approximately 10% of cases further therapy is required, such as systemic glucocorticoids or orbital radiotherapy. Surgical orbital decompression is reserved for those patients in which vision is threatened, where there is the presence of severe cosmetic deformity, or failure of medical management.